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Volume 45(3), September 1999, p 549
Microsurgical Anatomy of the Temporal Lobe: Part
1: Mesial Temporal Lobe Anatomy and Its
Vascular Relationships as Applied to
Amygdalohippocampectomy
[Anatomic Report]
Wen, Hung Tzu M.D.; Rhoton, Albert L. Jr. M.D.; de Oliveira,
Evandro M.D.; Cardoso, Alberto C. C. M.D.; Tedeschi, Helder
M.D.; Baccanelli, Matteo M.D.; Marino, Raul Jr. M.D.
Department of Neurological Surgery (ALR), University of Florida,
Gainesville, Florida; Institute of Neurological Sciences (HTW, EdO, HT, MB),
São Paulo; and Division of Neurosurgery, Hospital das Clínicas, University of
São Paulo (HTW, EdO, ACCC, HT, RM), São Paulo, Brazil
Received, October 28, 1998.
Accepted, April 14, 1999.
Reprint requests: Albert L. Rhoton, Jr., M.D., Department of Neurological
Surgery, University of Florida, 100 S. Newell Drive, Building 59, Room L2-100,
Gainesville, FL 32610-0265, or Hung Tzu Wen, M.D., Pça Amadeu Amaral 27,
5 andar, Bela Vista 01327-010, São Paulo (SP), Brazil.
Abstract
OBJECTIVE: We review the anatomy of the mesial temporal lobe region, establishing the
relationships among the intraventricular, extraventricular, and surrounding vascular structures and
their angiographic characterization. We also demonstrate the clinical application of these anatomic
landmarks in an anatomic temporal lobectomy plus amygdalohippocampectomy.
METHODS: Fifty-two adult cadaveric hemispheres and 12 adult cadaveric heads were studied,
using a magnification ranging from 3× to 40×, after perfusion of the arteries and veins with colored
latex.
RESULTS: The intraventricular elements are the hippocampus, fimbria, amygdala, and choroidal
fissure; the extraventricular elements are the uncus and parahippocampal and dentate gyri. The
uncus has an anterior segment, an apex, and a posterior segment that has an inferior and a
posteromedial surface; the uncus is related medially to cisternal elements and laterally to
intraventricular elements. The anterior segment is related to the proximal sylvian fissure, internal
carotid artery, proximal M1 segment of the middle cerebral artery, proximal cisternal anterior
choroidal artery, and amygdala. The apex is related to the oculomotor nerve, uncal recess, and
amygdala; the posteromedial surface is related to the P2A segment of the posterior cerebral artery
inferiorly, to the distal cisternal anterior choroidal artery superiorly, and to the head of the
hippocampus and amygdala intraventricularly. The choroidal fissure is located between the
thalamus and fimbria; it begins at the inferior choroidal point behind the head of the hippocampus
and constitutes the medial wall of the posterior two-thirds of the temporal horn.
CONCLUSION: Not only is the knowledge of these relations useful to angiographically characterize
the mesial temporal region, but it has also proven to be of extreme value during microsurgeries
involving this region.
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There are several features that make the temporal lobe unique; histologically, the temporal
lobe presents areas of different cortical organization, such as the three-layered allocortex, which
includes the prepiriform area, the semilunar gyrus of the uncus, and the hippocampus (74); the
six-layered mesocortex, which includes the parahippocampal gyrus; and the six-layered isocortex,
which includes the superior, middle, inferior, and transverse temporal gyri and the fusiform gyrus.
There is thus a gradual transition from a more primitive allocortex in the mesial temporal area to
the more recent isocortex located mainly in the lateral temporal area, with a transitional area, the
basal temporal area. This differentiation in cortical organization plays an important role in making
the temporal lobe the preferred site for certain tumors and epilepsy.
Anatomically, the temporal lobe also presents peculiarities; its superior surface is the temporal
operculum of the sylvian fissure, where the middle cerebral artery travels before sending off
branches to almost the entire lateral surface of the brain; the sylvian fissure is a frequent site for
cranial aneurysms, and it is the most frequently adopted route in neurosurgery to approach the
contents of the basal cisterns, the insula, the mesial temporal region, and less frequently, the basal
ganglia (transsylvian approach). The mesial surface of the temporal lobe is highly related to the
pathogenesis of mesial temporal lobe epilepsy; it is separated from the thalamus by the choroidal
fissure, which, despite being an embryological fissure, is one of the most important anatomic
landmarks noted by neurosurgeons when they disconnect the temporal lobe from the rest of the
brain. In addition to being a frequent site for aneurysms, the temporal lobe is also a common
location for vascular malformations, such as arteriovenous malformations and cavernomas (5, 57,
73).
Because of its location behind the sphenoid wing, temporal lobe contusion is a frequent event
in head trauma, often with surgical implications.
The temporal lobe is a unique structure in the human brain and has tremendous neurosurgical
importance; therefore, its microsurgical anatomy certainly requires better evaluation and
understanding. Numerous articles, reports, and textbooks have reported on the anatomy of the
temporal lobe (2, 38, 39, 52, 66, 68); however, a detailed description of temporal lobe anatomy that is
appropriate to fulfill the needs of the microneurosurgeon is still lacking. There have been some
lessons learned—and many questions raised—by the authors as they have performed
microsurgeries on human brains through the years; not surprisingly, most of the answers have
come from dissections performed in the anatomic laboratory.
Owing to the considerable amount of information to be presented, the microsurgical anatomy of
the temporal lobe will be discussed in three parts. In Part 1, the focus will be on the anatomy of the
mesial temporal lobe, with its practical application demonstrated by a stepwise dissection of the
standard anatomic temporal lobectomy. In Part 2, the anatomy of the sylvian fissure region will be
discussed. In Part 3, the anatomy of the lateral and basal aspects of the temporal lobe will be
reviewed.
TEMPORAL LOBE ANATOMY: GENERAL CONSIDERATIONS
Neural relationship
The limits of the temporal lobe are arbitrary; on the lateral surface, it is separated from the
frontal and parietal lobes by the posterior ramus of the sylvian fissure (Fig. 1), and it is separated
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from the occipital lobe by the lateral parietotemporal line, which runs from the impression of the
parieto-occipital fissure on the lateral surface to the preoccipital notch (Fig. 2); in its posterior
portion, the temporal lobe is separated from the parietal lobe by the temporo-occipital line, which
runs from the posterior end of the posterior ramus of the sylvian fissure to the midpoint of the
lateral parietotemporal line (Fig. 2). On the basal surface, it is separated from the occipital lobe by
the basal parietotemporal line, which connects the preoccipital notch to the inferior end of the
parieto-occipital fissure (Fig. 3) (42).
FIGURE 1. Superolateral view of the left hemisphere. The posterior ramus of the sylvian fissure
separates the temporal lobe inferiorly from the frontal and the parietal lobes superiorly. 1,
precentral sulcus; 2, central sulcus; 3, postcentral sulcus; 4, precentral gyrus; 5, postcentral
gyrus; 6, supramarginal gyrus; 7, ascending and descending terminations of the posterior ramus of
the sylvian fissure; 8, pars triangularis (inferior frontal gyrus); 9, pars opercularis (inferior frontal
gyrus); 10, Heschl’s gyrus (anterior transverse temporal gyrus); 11, middle temporal transverse
gyrus; 12, pars orbitalis (inferior frontal gyrus); 13, posterior ramus of the sylvian fissure; 14,
superior temporal gyrus; 15, superior temporal sulcus; 16, middle temporal gyrus; 17, inferior
temporal sulcus; 18, inferior temporal gyrus.
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FIGURE 2. Posterolateral view of the left hemisphere. The lateral parietotemporal line extends from
the impression of the parieto-occipital fissure on the lateral surface to the preoccipital notch, and it
separates the parietal and temporal lobes from the occipital lobe. The temporo-occipital line runs
from the posterior end of the posterior ramus of the sylvian fissure to the midpoint of the lateral
parietotemporal line, and it separates the temporal lobe from the parietal lobe. The intraparietal
sulcus separates the superior parietal lobule from the inferior parietal lobule that is constituted by
the supramarginal and the angulary gyri. 1, precentral gyrus; 2, postcentral gyrus; 3, intraparietal
sulcus; 4, superior parietal lobule; 5, supramarginal gyrus; 6, angulary gyrus; 7, temporo-occipital
line; 8, superior temporal gyrus; 9, middle temporal gyrus; 10, lateral parietotemporal line; 11,
occipital lobe.
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FIGURE 3. Basal view. The basal parietotemporal line that connects the preoccipital notch to the
inferior end of the parieto-occipital fissure separates the temporal lobe from the occipital lobe on
the basal surface of the brain. 1, olfactory tract; 2, optic nerve; 3, mamillary bodies; 4, optic tract
and uncus; 5, rhinal sulcus; 6, parahippocampal gyrus; 7, collateral sulcus; 8, fusiform gyrus; 9,
occipitotemporal sulcus; 10, pineal gland and splenium of the corpus callosum; 11, inferior
temporal gyrus; 12, basal parietotemporal line; 13, lingual gyrus.
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Anatomically, the temporal lobe continues posteriorly with the occipital lobe as the lingual
gyrus; functionally, however, the parahippocampal gyrus on the basal surface continues posteriorly
and superiorly with the cingulate gyrus through the isthmus of the cingulate gyrus (Fig. 13). The
temporal lobe is connected superiorly to the insula through the temporal stem, anteriorly and
medially to the globus pallidus via the amygdala (Figs. 24 and 25), and anteriorly and laterally to the
basal frontal lobe via the limen insulae (Figs. 4 and 5). The medial portion of the temporal lobe
behind the uncus is separated from the thalamus by the choroidal fissure.
FIGURE 4. Lateral view of the insula. The frontal and parietal opercula have been removed to
display the insula; the temporal stem that links the temporal lobe to insula, posteriorly to the limen
insulae, has been removed through its inferior circular sulcus, and the transverse temporal gyri
along with the lateral wall of the atrium of the lateral ventricle have also been resected to display
the relationships among the insula, the temporal lobe, and the lateral ventricle. The temporal lobe
is connected superiorly to the insula through the temporal stem and anteriorly and laterally to the
basal frontal lobe via the limen insulae. The central sulcus of the insula separates the short gyri
anteriorly from the long gyri of the insula posteriorly. 1, central sulcus; 2, superior limiting sulcus
of the insula; 3, central sulcus of the insula; 4, atrium of the lateral ventricle; 5, anterior limiting
sulcus of the insula; 6, inferior circular sulcus or inferior limiting sulcus of the insula; 7, orbital
surface of the frontal lobe; 8, limen insulae; 9, temporal horn; 10, middle temporal gyrus.
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FIGURE 5. An axial cut has been performed on the basal surface of the right temporal lobe; the
temporal pole and the temporal operculum of the sylvian fissure have been removed as well. The
temporal lobe is connected anteriorly and laterally to the basal frontal lobe via the limen insulae
and anteriorly and medially to the globus pallidus via the amygdala. The proximal half of the M1
segment is related superiorly to the anterior perforated substance, posteriorly to the semilunar
gyrus and the temporal amygdala, and inferiorly to the entorhinal area of the uncus. The anterior
perforated substance is limited anteriorly by the lateral and medial olfactory striae, posterolaterally
by the uncus, and posteromedially by the optic chiasm and the optic tract. 1, lateral orbital gyrus;
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2, anterior orbital gyrus; 3, medial orbital gyrus; 4, rectus gyrus; 5, olfactory tract; 6, posterior
orbital gyrus; 7, optic nerve; 8, M1 segment of the middle cerebral artery; 9, anterior perforated
substance; 10, M2 segment of the middle cerebral artery; 11, limen insulae; 12, amygdala; 13,
precentral gyrus; 14, temporal horn; 15, hippocampus; 16, medial geniculate body; 17, atrium.
FIGURE 13. Medial view of the right hemisphere. The temporal lobe continues posteriorly with the
occipital lobe as the lingual gyrus; however, functionally the parahippocampal gyrus continues
posteriorly and superiorly with the cingulate gyrus through the isthmus of the cingulate gyrus. The
mesial temporal lobe is constituted by the uncus, subiculum, dentate gyrus, choroidal fissure, and
fimbria. At its posterior portion just below the splenium of the corpus callosum, the
parahippocampal gyrus is often intersected by the anterior calcarine sulcus, which divides the
posterior portion of the parahippocampal gyrus into the isthmus of the cingulate gyrus, which
continues superiorly as the cingulate gyrus, and the parahippocampal gyrus inferiorly, which
continues posteriorly as the lingual gyrus. The dentate gyrus continues anteriorly with the band of
Giacomini (also called tail of the dentate gyrus), and posteriorly, it continues with the fasciolar
gyrus, a smooth grayish band that is located posterior to the splenium of the corpus callosum and
continues above the corpus callosum as the indusium griseum to finally end at the paraterminal
gyrus. 1, central sulcus; 2, postcentral gyrus; 3, postcentral sulcus; 4, cingulate sulcus; 5,
marginal ramus of the cingulate sulcus; 6, cingulate gyrus; 7, corpus callosum; 8, subparietal
sulcus; 9, precuneus; 10, parieto-occipital sulcus; 11, caudate nucleus; 12, isthmus of the
cingulate gyrus; 13, cuneus; 14, thalamus; 15, calcarine sulcus; 16, fornix; 17, dentate and
fasciolar gyri; 18, anterior calcarine sulcus; 19, lingual gyrus; 20, anterior perforated substance;
21, uncus; 22, parahippocampal gyrus; 23, rhinal sulcus; 24, collateral sulcus; 25, fusiform gyrus.
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FIGURE 24. Frontal view of the brain. A coronal cut has been performed at the level of the optic
chiasm on the left side of the specimen, and another coronal cut has been performed at the level of
the foramen of Monro and the apex of the uncus on the right side of the specimen. The temporal
lobe is connected superiorly to the insula through the temporal stem. The temporal amygdala
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blends superiorly into the globus pallidus without any clear demarcation; inferiorly, the posterior
portion of the temporal amygdala bulges from the most anterior portion of the roof of the temporal
horn toward the superior part of the hippocampal head, and frequently they merge. 1, superior
limiting or superior circular sulcus of the insula; 2, internal capsule; 3, thalamus; 4, insula; 5,
extreme capsule, claustrum, and external capsule; 6, globus pallidus (with its medial and lateral
parts); 7, inferior circular or inferior limiting sulcus of the insula; 8, amygdala; 9, apex of the
uncus; 10, temporal horn and collateral eminence; 11, head of the hippocampus; 12, anterior
segment of the uncus; 13, optic nerve; 14, limen insulae; *, temporal stem.
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FIGURE 25. A magnified view of Figure 24 to display the relationship among the head of the
hippocampus, the amygdala, and the globus pallidus.
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The temporal lobe has four surfaces: 1) the basal surface, 2) the lateral surface, 3) the
superior or opercular surface, and 4) the mesial surface. The basal surface is composed laterally to
medially of part of the inferior temporal gyrus, the occipitotemporal sulcus, the fusiform gyrus, the
collateral sulcus, and the parahippocampal gyrus (Fig. 3). The lateral surface is represented by the
superior, middle, and inferior temporal gyri, separated by the superior and inferior temporal sulci
(Figs. 1 and 2). These two surfaces will be discussed in detail in Part 3 of this study. The superior
surface is also called the opercular surface, and it is the temporal operculum of the sylvian fissure.
It presents three morphologically distinct parts (the planum polare, Heschl’s gyrus, and the planum
temporale) and will be discussed in detail in Part 2 of this study (Fig. 6).
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FIGURE 6. Superior view of the left temporal lobe. It has been disconnected medially from the
thalamus through the choroidal fissure, anteriorly and medially from the globus pallidus, anteriorly
and laterally from the insula, and superiorly from the temporal stem. The superior surface is also
called the opercular surface, and it is the temporal operculum of the sylvian fissure. It presents
three morphologically distinct parts: the planum polare, Heschl’s gyrus, and the planum temporale
(usually formed by the middle and posterior transverse temporal gyri). The temporal lobe along
with the occipital lobe resembles the shape of a foot: the dorsum of the foot is represented by the
temporal operculum of the sylvian fissure, the syndactylic second through fifth toes are represented
by the planum polare, the hallux is represented by the uncus, and the area between the hallux and
the second toe is represented by the extension of the rhinal sulcus on the dorsal surface of the
temporal lobe, separating the uncus medially from the planum polare laterally. 1, cuneus (floor of
the parieto-occipital fissure); 2, calcar avis; 3, lateral wall of the atrium; 4, posterior transverse
temporal gyrus; 5, middle transverse temporal gyrus; 6, Heschl’s gyrus (anterior transverse
temporal gyrus); 7, parahippocampal gyrus; 8, body of the hippocampus and fimbria; 9, dentate
gyrus; 10, temporal stem (cut); 11, head of the hippocampus; 12, uncus; 13, limen insulae; 14,
rhinal sulcus; 15, superior temporal gyrus; 16, planum polare.
When completely disconnected from the insula, the globus pallidus, and the thalamus, the
shape of the temporal lobe along with the occipital lobe roughly resembles a foot; the occipital pole
represents the calcaneus, the curvature of the basal temporal lobe over the petrous bone
represents the plantar arch, and the temporal lobe descending into the middle fossa represents the
plantar prominence (Fig. 7). When viewed from above, the dorsum of the foot is represented by the
temporal operculum of the sylvian fissure (with the difference that, owing to the temporal gyri on
the lateral surface, the temporal operculum is higher laterally and then descends from lateral to
medial), the syndactylic second through the fifth toes correspond to the planum polare (the
anterior portion of the temporal operculum), the hallux is represented by the uncus, and the area
between the hallux and the second toe is represented by the extension of the rhinal sulcus on the
dorsal surface of the temporal lobe, separating the uncus medially from the planum polare laterally
(Fig. 6). When viewed from a lateral perspective, the lateral surface of the temporal lobe is
represented by three temporal gyri (superior, middle, and inferior) (Fig. 2), and when viewed from a
medial perspective, the temporal lobe is represented by the uncus, the subiculum, which is the
round medial edge of the parahippocampal gyrus, the thin dentate gyrus, the choroidal fissure, and
the fimbria (Fig. 13); as the basal surface of the temporal lobe is relatively flat, the medial temporal
surface is thinner than the lateral surface, and the superior surface of the temporal lobe descends
laterally to medially when it is viewed from its anterior aspect.
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FIGURE 7. Medial view of the temporal and occipital lobes (same specimen shown in Fig. 6). The
temporal lobe along with the occipital lobe presents the roughly estimated shape of a foot, with the
calcaneus represented by the occipital pole, the plantar arch by the curvature of the basal temporal
lobe over the petrous bone, and the plantar prominence by the temporal lobe descending into the
middle fossa. 1, parieto-occipital fissure; 2, splenium of the corpus callosum; 3, Heschl’s gyrus; 4,
cuneus; 5, isthmus of the cingulate gyrus; 6, body of the hippocampus and fimbria; 7, temporal
stem; 8, planum polare; 9, calcarine sulcus; 10, anterior calcarine sulcus; 11, inferior choroidal
point; 12, posterior segment of the uncus; 13, apex of the uncus; 14, anterior segment of the
uncus; 15, rhinal sulcus; 16, lingual gyrus; 17, parahippocampal gyrus.
Osseous relationship
Anteriorly, the temporal lobe is related mainly to the greater wing of the sphenoid bone,
inferiorly to the floor of the middle fossa and the petrous bone (Figs. 8 and 9, and laterally to the
squamous part of the temporal bone; however, the posterior part of the lateral temporal lobe rises
more superiorly, remains beyond the limits of the squamous suture, and is related to the parietal
bone (Fig. 10). . The part of the mesial temporal lobe that is located above the tentorial groove
normally herniates medially to the free edge of the tentorium and is related medially to the carotid,
crural, interpeduncular, and ambient cisterns (Fig. 11); the part of the mesial temporal lobe that is
located below the tentorial groove is related to the cavernous sinus (Fig. 12).
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FIGURE 8. Posterosuperior view of the skull base. Anteriorly, the temporal lobe is related mainly to
the greater wing of the sphenoid bone, inferiorly to the floor of the middle fossa and the petrous
bone. 1, lesser wing of the sphenoid; 2, superior orbital fissure; 3, anterior clinoidal process; 4,
tuberculum sellae; 5, internal carotid artery (cavernous segment); 6, foramen rotundum; 7,
dorsum sellae; 8, sphenosquamosal suture; 9, foramen ovale; 10, clivus; 11, petrous apex; 12,
internal acoustic meatus; 13, semicircular canals; 14, jugular foramen; 15, hypoglossal canal.
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FIGURE 9. Superior view of the skull base with intact dura mater. The temporal lobe is related
inferiorly to the floor of the middle fossa and the petrous bone. 1, orbit; 2, lesser wing of the
sphenoid; 3, anterior clinoid process; 4, optic nerve and internal carotid artery; 5, middle fossa and
middle meningeal artery; 6, oculomotor nerve; 7, basilar artery; 8, petrous bone and arcuate
eminence; 9, cerebellomesencephalic fissure, trochlear nerve, and branches of the superior
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cerebellar artery; 10, tentorium edge; 11, straight sinus.
FIGURE 10. Lateral view of the left hemisphere; the coronal, squamous, and lambdoid sutures were
kept in place. The temporal lobe is related laterally to the squamous part of the temporal bone,
except the posterior part of the superior and middle temporal gyri, which is related to the parietal
bone. 1, coronal suture; 2, precentral gyrus; 3, postcentral gyrus; 4, posterior ramus of the sylvian
fissure; 5, superior temporal gyrus; 6, squamous suture; 7, middle temporal gyrus; 8, lambdoid
suture.
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FIGURE 11. Basal view of the brain. The part of the mesial temporal lobe that is located above the
tentorial groove normally herniates medially to the free edge of the tentorium, and it is related
medially to the carotid, crural, interpeduncular, and ambient cisterns. 1, olfactory tract; 2, rhinal
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sulcus; 3, optic nerve; 4, anterior segment of the uncus; 5, tentorial groove; 6, apex of the uncus;
7, anterior hippocampal sulcus; 8, posterior segment of the uncus; 9, crus cerebri; 10,
parahippocampal gyrus; 11, lateral mesencephalic sulcus; 12, medial geniculate body; 13,
collateral sulcus; 14, pulvinar of the thalamus; 15, splenium of the corpus callosum.
FIGURE 12. Lateral view of the right cavernous sinus; the lateral wall of the cavernous sinus has
been peeled off to display the contents of the cavernous sinus. The anterior clinoid process and the
tentorium have been removed as well. The part of the mesial temporal lobe that is located below
the tentorial groove is related to the cavernous sinus. 1, basilar artery; 2, pituitary gland; 3,
supraclinoidal segment of the internal carotid artery and ophthalmic artery; 4, optic nerve and
sphenoid sinus; 5, trochlear nerve; 6, superior cerebellar artery; 7, posterior bend of the cavernous
carotid artery and oculomotor nerve; 8, tentorial edge; 9, trigeminal nerve; 10, V1 and trochlear
nerve; 11, Gasserian ganglion; 12, V2; 13, petrous apex; 14, V3; 15, facial and superior vestibular
nerves; 16, petrous carotid artery; 17, geniculate ganglion; 18, middle meningeal artery; 19,
semicircular canals.
MESIAL TEMPORAL LOBE ANATOMY
The role played by the temporal amygdala, entorhinal area, allocortex, mesocortex, and
hippocampus in the genesis and circuitry of mesial temporal lobe epilepsy is becoming clearer (34,
55, 61),
as is the importance of removal of these structures in seizure control of intractable temporal
epilepsy (1, 15, 23, 24, 40, 45, 70, 71); however, the intraoperative identification of these structures
still constitutes a formidable challenge for neurosurgeons.
The authors’ experience in microsurgical exploration of the mesial temporal lobe in tumors,
arteriovenous malformations, and mesial temporal sclerosis at the Hospital das Clínicas and the
Neurological Institute of São Paulo, along with the anatomic dissections performed in the anatomy
laboratory at the Department of Neurological Surgery, University of Florida, over the last 4 years,
have assured authors of the necessity of reestablishing some important concepts about the
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anatomy of the mesial temporal lobe from the neurosurgical standpoint: 1) the components and
the surgical limits of the uncus; 2) the relationship between the uncus and the hippocampus; 3) the
relationship between the uncus and the cavity of the temporal horn; 4) the relationship among the
uncus, the hippocampus, and the temporal amygdala; 5) the relationship of the uncus to the
internal carotid, posterior communicating, anterior choroidal, posterior cerebral, and middle
cerebral arteries and the basal vein of Rosenthal; 6) the angiographic characterization of the
uncus; 7) the role played by the choroidal fissure of the temporal horn in surgeries involving the
temporal lobe; and 8) the surgical limits of the temporal amygdala.
Because the angiogram essentially demonstrates the temporal anatomy by visualization of the
vessels, the angiographic correlation of the anatomic dissections will be displayed in this article. An
extensive number of illustrations will be presented because we think that, for acquisition of
tridimensional knowledge in anatomy, the same neural or vascular structure must be seen from
different angles.
MATERIALS AND METHODS
Fifty-two adult hemispheres and 12 adult cadaveric heads in which the arteries and veins were
injected with colored silicone were examined under the microscope with magnifications varying
from 3× to 40×. All bone work was performed with a high-speed drill (Midas Rex Institute, Fort
Worth, TX).
Neural relationships
The neural structures that constitute the mesial temporal lobe are the parahippocampal gyrus,
uncus, hippocampus, fimbria, dentate gyrus, and amygdala. The extraventricular components of
the mesial temporal lobe are the parahippocampal gyrus, uncus, and dentate gyrus.
Parahippocampal gyrus
The parahippocampal gyrus occupies the transitional area between the basal and the mesial
surfaces of the temporal lobe. It extends anteriorly to posteriorly, and at its anterior extremity, it
deviates medially and bends posteriorly to constitute the uncus. Posteriorly, just below the
splenium of the corpus callosum, it is often intersected by the anterior calcarine sulcus, which
divides the posterior portion of the parahippocampal gyrus into the isthmus of the cingulate gyrus
superiorly, which continues as the cingulate gyrus, and the parahippocampal gyrus inferiorly, which
continues posteriorly as the lingual gyrus, the floor of the calcarine sulcus (Fig. 13).
The parahippocampal gyrus follows the tentorium edge and encircles the brainstem posteriorly,
as does the tentorium edge, to constitute the tentorial incisura (43). Superiorly, the
parahippocampal gyrus is separated from the dentate gyrus by the hippocampal sulcus (Fig. 14).
Laterally, the parahippocampal gyrus is limited at its posterior portion by the collateral sulcus,
which bulges superiorly into the lateral part of the floor of the temporal horn as the collateral
eminence anteriorly and the collateral trigone posteriorly (60); the location of the collateral sulcus
and consequently the location of the lateral part of the floor of the temporal horn can be
determined angiographically by following the inferior temporal branches of the posterior cerebral
artery as they descend into the depth of the collateral sulcus before continuing on the surface of
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the fusiform gyrus (25, 51).
FIGURE 14. Magnified view of Figure 13. The parahippocampal gyrus is separated superiorly from the
dentate gyrus by the hippocampal sulcus. The uncal notch is the sulcus located between the uncus
superiorly and the parahippocampal gyrus inferiorly. The uncus continues anteriorly with the
anterior portion of the parahippocampal gyrus without a sharp limit, and it is continuous superiorly
with the globus pallidus. The fimbrodentate and hippocampal sulci separate the dentate gyrus
respectively from the fimbria of the fornix superiorly and the parahippocampal gyrus inferiorly. The
dentate gyrus continues anteriorly with the band of the Giacomini, and posteriorly it continues with
the fasciolar gyrus located behind the splenium of the corpus callosum and continues above the
corpus callosum as the indusium griseum to finally end at the paraterminal gyrus. 1, fasciolar
gyrus; 2, fornix; 3, dentate gyrus; 4, choroidal fissure (between the fornix and the thalamus); 5,
fimbrodentate sulcus; 6, hippocampal sulcus; 7, uncus; 8, uncal notch; 9, parahippocampal gyrus;
10, fusiform gyrus; 11, planum polare.
At its anterior portion, the parahippocampal gyrus is limited laterally by the rhinal sulcus (Fig.
15).
The rhinal sulcus marks the lateral limit of the entorhinal area of the parahippocampal gyrus
(13). Anteriorly, the parahippocampal gyrus is related to the greater wing of the sphenoid;
anterosuperiorly, it is related to the uncus; the uncal notch separates the inferior surface of the
posterior segment of the uncus (described below) superiorly from the parahippocampal gyrus
inferiorly. Medially, the parahippocampal gyrus is related to the free edge of the tentorium and to
the contents of the ambient cistern. The various components of the parahippocampal gyrus are the
subiculum, presubiculum, parasubiculum, and entorhinal area (48, 66, 68). The subiculum is the
medial round edge of the parahippocampal gyrus.
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FIGURE 15. Basal view of the right hemisphere. The parahippocampal gyrus is limited laterally by
the collateral sulcus; at its anterior portion, the parahippocampal gyrus is limited laterally by the
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rhinal sulcus. The uncus is separated laterally from the temporal pole by the rhinal sulcus. The
uncus presents the shape of an arrowhead, featuring an apex and anterior and posterior segments;
the posterior segment is separated inferiorly from the parahippocampal gyrus by the uncal notch.
1, temporal pole; 2, anterior perforated substance; 3, anterior segment of the uncus; 4, rhinal
sulcus; 5, apex of the uncus; 6, posterior segment of the uncus and uncal notch; 7,
parahippocampal gyrus; 8, fornix; 9, dentate and fasciolar gyri; 10, splenium of the corpus
callosum; 11, fusiform gyrus; 12, collateral sulcus; 13, isthmus of the cingulate gyrus.
Uncus
The name uncus means “hook.” It is formed by the anterior portion of the parahippocampal
gyrus, which has deviated medially and folded posteriorly. This process forms a sulcus between the
parahippocampal gyrus and the uncus, the “uncal notch” (13).
Inferiorly, the uncus is separated from the parahippocampal gyrus by the uncal notch.
Anteriorly, the uncus continues with the anterior portion of the parahippocampal gyrus without a
sharp limit; superiorly, the uncus is continuous with the globus pallidus (Fig. 14). At the basal
surface, the uncus is separated laterally from the temporal pole by the rhinal sulcus (Fig. 15). As
mentioned above, the medial part of the uncus is normally herniated medially to the tentorial edge.
When viewed from its basal surface, the uncus presents the shape of an arrowhead with its
apex pointing medially, featuring an apex, an anterior segment, and a posterior segment. The
posterior segment is separated inferiorly from the parahippocampal gyrus by the uncal notch (Fig.
15).
The components and the overall shape of the uncus can be better visualized from its medial
aspect, however. The overall shape of the uncus resembles the diagonal half of a midtransversely
sectioned square-based pyramid. When regarded from above and medially, this half-pyramid
presents an anterior and a posterior wall that converge medially into an edge; the posterior wall is
further divided into upper and a lower halves by a transversely directed fissure.
In this article, the anterior wall, the edge, and the upper half of the posterior wall will be
designated, respectively, as the anterior segment, the apex, and the posterior segment of the
uncus; the transversely directed fissure is the uncal notch that separates the posterior segment of
the uncus superiorly from the parahipppocampal gyrus inferiorly. The anterior segment of the
uncus presents one surface, the anteromedial surface, whereas the posterior segment presents two
surfaces, a posteromedial and an inferior surface, which is the upper wall of the uncal notch. Both
segments converge superiorly to the junction between the amygdala and the globus pallidus (Fig.
16).
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FIGURE 16. Medial view of an illustrative diagram of the uncus. The overall shape of the uncus
resembles that of the diagonal half of a midtransversely sectioned square-based pyramid. When
viewed from above and medially, this half-pyramid presents an anterior and a posterior wall that
converge medially into an edge; the posterior wall is further divided into upper and lower halves by
a transversely directed fissure. 1, globus pallidus; 2, anteromedial surface of the uncus; 3,
posteromedial surface of the uncus; 4, uncal notch; 5, parahippocampal gyrus; 6, apex of the
uncus.
The uncus is composed of five small gyri and a small part of the entorhinal area, which occupies
the anterior part of the anteromedial surface of the uncus. The semilunar and ambient gyri belong
to the anterior segment, and the uncinate gyrus, the band of Giacomini, and the intralimbic gyrus
belong to the posterior segment (6, 7, 13, 41).
The anterior segment or anteromedial surface of the uncus belongs to the parahippocampal
gyrus and presents two small gyri: the semilunar gyrus and the ambient gyrus. The semilunar
gyrus occupies the superior portion of this surface and is bordered inferiorly by the sulcus
annularis; the ambient gyrus is medial and inferior to the semilunar gyrus; the anteroinferior area
of this surface is occupied by the entorhinal area, which continues anteriorly and inferiorly with the
entorhinal area of the parahippocampal gyrus. The anteromedial surface is related to the proximal
sylvian fissure and the carotid cistern and is the posterolateral limit of the anterior perforated
substance (49).
The posterior segment is related to the hippocampus and has two surfaces: a posteromedial
and an inferior surface. The posteromedial surface is occupied by three small gyri; from anterior to
posterior, they are the uncinate gyrus, the band of Giacomini, and the intralimbic gyrus. The
distribution of these three gyri, in addition to the two gyri of the anterior segment, resembles that
of five sections of a pumpkin that are all attached superiorly. The superior and inferior portions of
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the posteromedial surface of the uncus are related, respectively, to the crural and ambient cisterns.
Posteriorly and superiorly to the uncus is the inferior choroidal point, where the choroid plexus of
the temporal horn begins; this also usually corresponds to the site where the anterior choroidal
artery enters the temporal horn through the choroidal fissure (Fig. 17).
FIGURE 17. Medial view of the uncus and the mesial temporal region. The anterior segment or
anteromedial surface of the uncus belongs to the parahippocampal gyrus and presents two small
gyri: the semilunar gyrus, which is bordered inferiorly by the sulcus semiannularis, and the ambient
gyrus; the anteroinferior area of this surface is occupied by the entorhinal area, which continues
anteriorly and inferiorly with the entorhinal area of the parahippocampal gyrus. The anteromedial
surface is related to the proximal sylvian fissure and the carotid cistern and is the posterolateral
limit of the anterior perforated substance. The posterior segment is related to the hippocampus,
and it has two surfaces: a posteromedial and an inferior surface. The posteromedial surface is
occupied by three small gyri: from anterior to posterior are the uncinate gyrus, band of Giacomini,
and intralimbic gyrus. The distribution of these three gyri in addition to the two gyri of the anterior
segment resembles five sections of a pumpkin that are all attached superiorly. The superior and
inferior portions of the posteromedial surface of the uncus are related respectively to the crural and
ambient cisterns. The apex of the uncus is constituted by the ambient and uncinate gyri. Posteriorly
and superiorly to the uncus is the choroidal point, where the choroid plexus of the temporal horn
begins and usually corresponds to where the anterior choroidal artery enters the temporal horn. 1,
rectus gyrus; 2, olfactory tract; 3, anterior perforated substance; 4, semilunar gyrus; 5, ambient
gyrus; 6, fimbria; 7, dentate gyrus; 8, semiannularis sulcus; 9, uncinate gyrus; 10, band of
Giacomini; 11, intralimbic gyrus; 12, uncal notch; 13, rhinal sulcus; 14, collateral sulcus; *,
entorhinal area.
The inferior surface is located under the posterior segment of the uncus and is visible only from
below when the parahippocampal gyrus is removed (Fig. 18). It is the superior lip of the uncal notch
and is composed anteriorly to posteriorly by the external digitations of the uncus (uncinate gyrus),
the band of the Giacomini, and the intralimbic gyrus. The inferior lip of the uncal notch is
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represented by the parahippocampal gyrus.
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FIGURE 18. Basal view of the left hemisphere. The parahippocampal gyrus has been removed from
the hippocampal sulcus posteriorly and from the uncal notch anteriorly. The inferior surface of the
posterior segment of the uncus can be visible only from below when the parahippocampal gyrus is
removed. It is the superior lip of the uncal notch and is composed from anterior to posterior by the
external digitations of the uncus (uncinate gyrus), the band of Giacomini, and the intralimbic gyrus.
The external digitations are two or three small lobules separated by sagittal sulci and emerge on
the inferior and posteromedial surfaces of the uncus as the uncinate gyrus. They correspond
intraventricularly to the hippocampal digitations of the head of the hippocampus and are formed
mainly by the CA1 field of the hippocampal formation. The external digitations are separated from
the band of Giacomini by the anterior hippocampal sulcus. The band of Giacomini is also called the
tail of the dentate gyrus; however, it loses its denticulations as it emerges from the fimbrodentate
sulcus and enters the roof of the uncal notch. The intralimbic gyrus contains sectors CA3 and CA4
of the hippocampal formation; it forms the posterior boundary of the uncus and is the site of
attachment to the fimbria. The fimbria widens as it approaches the intralimbic gyrus and spreads
out over the surface of the intralimbic gyrus. The fimbrodentate and hippocampal sulci separate the
dentate gyrus respectively from the fimbria superiorly and the parahippocampal gyrus inferiorly.
The midbrain is divided into two halves, the right and the left cerebral peduncles, by a sagittal
plane; the cerebral peduncle is demarcated into an anterior crus cerebri and a posterior tegmental
part by the substantia nigra. 1, rhinal sulcus; 2, anterior perforated substance; 3, tentorial groove;
4, uncinate gyrus; 5, band of Giacomini; 6, posterior perforated substance; 7, crus cerebri; 8,
intralimbic gyrus; 9, fimbria; 10, substantia nigra; 11, lateral geniculate body; 12, fimbrodentate
sulcus; 13, medial geniculate body; 14, dentate gyrus; 15, tegmentum; 16, pulvinar of the
thalamus; 17, choroidal fissure; 18, splenium of the corpus callosum; 19, fusiform gyrus.
The external digitations are two or three small lobules separated by sagittal sulci and emerge
on the posteromedial surface of the uncus as the uncinate gyrus. They are the convolutions of the
hippocampal allocortex that correspond intraventricularly to the hippocampal digitations of the head
of the hippocampus and are formed mainly by the CA1 field of the hippocampal formation. The
external digitations are separated from the band of Giacomini by the anterior hippocampal sulcus
(13).
The band of Giacomini is also called the tail of the dentate gyrus; however, it does not present
the denticulations that are the main features of the dentate gyrus. The dentate gyrus loses its
denticulations as it emerges from the fimbrodentate sulcus and enters the roof of the uncal notch.
The intralimbic gyrus contains the sectors CA3 and CA4 of the hippocampal formation (6, 7). Its
posterior bulge has the shape of a cone and forms the posterior boundary of the uncus; it is the
site of attachment to the fimbria. The fimbria widens as it approaches the intralimbic gyrus and
spreads out over the surface of the intralimbic gyrus (Fig. 18).
When viewed from an anterior perspective, the anteromedial segment of the uncus continues
superiorly toward the junction between the semilunar gyrus (cortical amygdala) and the globus
pallidus without any sharp demarcation between them. Lateral and anterior to the semilunar gyrus
and globus pallidus is the limen insulae.
Dentate gyrus
The dentate gyrus, along with the hippocampus, forms two parallel interlocking cylinders. On
the coronal cut, both present the shape of the letter “C”; the hippocampus is the concavity of the
“C” directed inferomedially, and the dentate gyrus represents the concavity of the “C” directed
superolaterally (13). The fimbrodentate and hippocampal sulci separate the dentate gyrus,
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respectively, from the fimbria of the fornix superiorly and the parahippocampal gyrus inferiorly
(Figs. 14 and 18).
The dentate gyrus bears this name because of its characteristic toothlike elevations; the margo
denticulatus is prominent mainly in its anterior and middle portions. The dentate gyrus continues
anteriorly with the band of Giacomini, also called the tail of the dentate gyrus, and continues
posteriorly with the fasciolar gyrus, a smooth grayish band that is located posteriorly to the
splenium of the corpus callosum; it continues above the corpus callosum as the indusium griseum
to finally end as the paraterminal gyrus (Fig. 13).
Hippocampus
Among the intraventricular components of the mesial temporal region, the hippocampus proper
occupies the medial part of the floor of the temporal horn and can be divided into three parts:
head, body, and tail (Figs. 19 and 20) (6, 7, 13, 32, 33, 60). The head of the hippocampus represents
the anterior and largest part of the hippocampus; it is directed first anteriorly and then medially. At
the medial end of the tip of the temporal horn, the head of the hippocampus turns up vertically and
bends over laterally, forming the medial wall of the tip of the temporal horn anterior to the
choroidal fissure. The head of the hippocampus is the only part of the hippocampus that is free of
choroid plexus. The posterior limit of the head of the hippocampus is characterized by the initial
segment of the fimbria and the choroidal fissure. The head of the hippocampus is characterized by
three or four hippocampal digitations, and its overall shape resembles that of a feline paw. The
origin of the hippocampal digitations is thought to be the result of some obstacle to forward
development of the hippocampus.
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FIGURE 19. Superior view of the brain. An axial cut has been performed, and the components of
the lateral ventricle have been unroofed mainly to display the floor of the temporal horn. 1, genu of
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the corpus callosum; 2, head of the caudate nucleus; 3, lentiform nucleus; 4, anterior commissure;
5, uncal recess; 6, thalamus; 7, head of the hippocampus; 8, body of the hippocampus; 9,
collateral eminence; 10, fimbria; 11, tail of the hippocampus; 12, collateral trigone 13, bulb of the
callosum.
FIGURE 20. Lateral view of Figure 19. The roof and the lateral wall of the right temporal horn as well
as the choroid plexus have been removed. The hippocampus proper occupies the medial part of the
floor of the temporal horn and can be divided into three parts: head, body, and tail. The head of
the hippocampus is the anterior and largest part of the hippocampus; it is directed anteriorly and
then medially. The head of the hippocampus is the only part of the hippocampus that is free of
choroid plexus, and it has its posterior limit marked by the initial segment of the fimbria and the
choroidal fissure. The head of the hippocampus is characterized by three or four hippocampal
digitations, and its overall shape resembles that of a feline paw. Anteriorly, the head of the
hippocampus is related to the uncal recess of the temporal horn, the part of the temporal horn that
is located between the anterior wall of the temporal horn and the head of the hippocampus; the
uncal recess actually is the continuation of the collateral eminence, which follows the anterior and
then medial turn of the hippocampus. The emergence of the choroid plexus, the fimbria, and the
choroidal fissure marks the beginning of the body of the hippocampus. The body of the
hippocampus has an anteroposterior and inferosuperior direction in the medial part of the floor of
the temporal horn and becomes narrower as it approaches the atrium of the lateral ventricle.
Running on its medial border is the fimbria of the fornix. Laterally, the body of the hippocampus is
related to the collateral eminence, the lateral part of the floor of the temporal horn. At the level of
the body and the tail of the hippocampus, the medial wall of the temporal horn is the choroidal
fissure, which communicates medially with the ambient cistern and the wing of the ambient cistern.
At the posterior end of the intraventricular portion of the pulvinar of the thalamus, the
hippocampus changes its direction and has its longitudinal axis oriented transversely once again, as
occurred with the head of the hippocampus. At the atrium, the tail of the hippocampus becomes
even more slender and makes up the medial part of the floor of the atrium. Laterally, it is related to
the collateral trigone; medially, the tail of the hippocampus fuses with the calcar avis. 1, splenium
of the corpus callosum; 2, left frontal horn; 3, fornix; 4, foramen of Monro; 5, bulb of the callosum;
6, thalamus; 7, internal capsule; 8, calcar avis; 9, tail of the hippocampus; 10, lateral geniculate
body, inferior ventricular vein (blue), and anterior choroidal artery (red); 11, globus pallidus; 12,
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collateral trigone; 13, body of the hippocampus and fimbria; 14, head of the hippocampus; 15,
amygdala.
The head of the hippocampus is directed toward the posterior segment of the uncus.
Superiorly, the head of the hippocampus is related to the posteroinferior portion of the amygdala,
which bulges from the most anterior part of the roof of the temporal horn into the ventricular cavity
and frequently fuses with the medial part of the head of the hippocampus. Anteriorly, the head of
the hippocampus is related to the uncal recess of the temporal horn, the part of the temporal horn
that is located between the anterior wall and the head of the hippocampus; the uncal recess
actually is the continuation of the collateral eminence, which follows the anterior and then medial
turn of the hippocampus.
The emergence of the choroid plexus, the fimbria, and consequently the choroidal fissure marks
the beginning of the body of the hippocampus. The body of the hippocampus has an
anteroposterior and inferosuperior direction in the medial part of the floor of the temporal horn,
and it becomes narrower as it approaches the atrium of the lateral ventricle. Running on its medial
border is the fimbria of the fornix. Laterally, the body of the hippocampus is related to the collateral
eminence, the lateral part of the floor of the temporal horn (Figs. 19 and 20). At the level of the body
of the hippocampus, the medial wall of the temporal horn becomes the choroidal fissure, which
communicates medially with the ambient cistern and the wing of the ambient cistern, which is the
part of the ambient cistern that opens laterally under the pulvinar of the thalamus.
At the posterior end of the intraventricular portion of the pulvinar of the thalamus, which
makes up the anterior wall of the atrium, the hippocampus changes its direction and has its
longitudinal axis oriented transversely once again, as occurred with the head of the hippocampus.
At the atrium, the tail of the hippocampus becomes even more slender and constitutes the medial
part of the floor of the atrium. Laterally, it is related to the collateral trigone (the lateral part of the
floor of the atrium); medially, the tail of the hippocampus fuses with the calcar avis (the inferior
bulging on the medial wall of the atrium). Therefore, viewed macroscopically, the tail of the
hippocampus ends when it meets the medial wall of the atrium, although histologically the terminal
segment of the hippocampal tail continues as the subsplenial gyrus, which covers the inferior
splenial surface (Figs. 19 and 20).
Fimbria
The ventricular surface of the hippocampus is covered by white matter, called alveus, which
thickens along the medial edge of the hippocampus to form the fimbria. The alveus represents the
subcortical white matter of the temporal lobe and constitutes the subcortical white matter of the
hippocampal allocortex. At the temporal lobe, the fimbria is separated from the dentate gyrus by
the fimbrodentate sulcus. The fimbria is the initial part of the fornix and passes posteriorly to
become the crus of the fornix; it represents the subcortical radiation of the hippocampal allocortex
(13). Each crus wraps around the posterior surface of the pulvinar of the thalamus and arches
superomedially toward the lower surface of the splenium of the corpus callosum. Both crura are
united by the hippocampal commissure, and in the body of the corpus callosum, the body of the
fornix constitutes the medial part of the floor (Fig. 21); at the level of the foramen of Monro, the
columns of the fornix constitute the superior and anterior limits of the foramen of Monro. The
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columns of the fornix then split, predominantly posterior to the anterior commissure
(postcommissural fibers), and are directed inferiorly and posteriorly through the lateral wall of the
third ventricle to reach the mamillary bodies at the floor of the third ventricle (Figs. 22 and 23).
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FIGURE 21. Superior view of the brain. An axial cut has been performed, and the lateral ventricle
has been unroofed to display the components of the fornix. The fimbria passes posteriorly to
become the crus of the fornix and represents the subcortical radiation of the hippocampal
allocortex. Each crus then wraps around the pulvinar of the thalamus and arches superomedially
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toward the lower surface of the splenium of the corpus callosum; both crura are united by the
hippocampal commissure, and in the body of the corpus callosum the body of the fornix constitutes
the medial part of the floor. 1, genu of the corpus callosum; 2, head of the caudate nucleus; 3,
columns of the fornix; 4, internal capsule; 5, thalamus; 6, body of the fornix; 7, hippocampal
commissure; 8, crus of the fornix; 9, tail of the hippocampus; 10, calcar avis; 11, collateral trigone.
FIGURE 22. At the level of the foramen of Monro, the columns of the fornix constitute the superior
and anterior limits of the foramen of Monro; the columns of the fornix then split, predominantly
posteriorly to the anterior commissure (postcommissural fibers) to direct inferiorly and posteriorly
through the lateral wall of the third ventricle to reach the mamillary bodies at the floor of the third
ventricle. Left superolateral view of the brain. An axial cut has been performed. 1, genu of the
corpus callosum; 2, septum pellucidum; 3, foramen of Monro; 4, splenium of the corpus callosum;
5, anterior commissure; 6, thalamus; 7, lentiform nucleus; 8, posterior limb of the internal capsule;
9, bulb of the callosum; 10, calcar avis; 11, tapetum (medially) and optic radiation.
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FIGURE 23. Frontal view of the brain. A coronal cut has been performed at the level of the optic
chiasm. 1, body of the corpus callosum; 2, body of the caudate nucleus; 3, septum pellucidum; 4,
thalamus; 5, columns of the fornix and foramina of Monro; 6, internal capsule; 7, lentiform
nucleus; 8, anterior commissure; 9, lamina terminalis; 10, limen insulae; 11, optic nerve; 12,
olfactory tract.
Amygdala
The amygdala, along with the hippocampus, constitutes the core of the limbic system. The
current concept of the amygdala complex divides it into the temporal or principal amygdala, which
is located in the temporal lobe, and the extratemporal or extended amygdala, which is located in
the primordial floor of the lateral ventricle and is part of the basal forebrain (13). In this study, only
the temporal or principal amygdala will be discussed.
The temporal amygdala is composed by a series of gray matter nuclei that can be classified into
three main groups: the basolateral, corticomedial, and central groups. The semilunar gyrus is part
of the cortical nucleus of the temporal amygdala (13).
From the neurosurgical viewpoint, the temporal amygdala can be considered as being entirely
located within the boundaries of the uncus: superiorly, the temporal amygdala blends into the
globus pallidus without any clear demarcation; inferiorly, the posterior portion of the temporal
amygdala bulges inferiorly from the most anterior portion of the roof of the temporal horn toward
the superior part of the hippocampal head, and frequently they become fused (Figs. 24 and 25);
medially, it is related to the anterior and posterior segments of the uncus; anteroinferiorly and
anterosuperiorly, it is related, respectively, to the entorhinal area and to the semilunar gyrus of the
anterior segment of the uncus.
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of the temporal horn and continues above the uncal recess. It also constitutes the anterior wall of
the temporal horn (Fig. 26). The temporal amygdala therefore is the anterior wall of the temporal
horn and also constitutes the most anterior part of the roof of the temporal horn above the uncal
recess and the head of the hippocampus, anterior to the inferior choroidal point, which is the
beginning of the choroid plexus in the temporal horn. These intricate relationships among the
temporal amygdala, globus pallidus, uncus, hippocampus, and temporal horn cavity are displayed
in Figures 27 to 30.
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FIGURE 26. Basal view of the brain. An axial cut has been performed on the right basal surface to
display the temporal horn and the atrium of the lateral ventricle. The amygdala is the roof of the
anterior portion of the temporal horn (above the head of the hippocampus, anterior to the inferior
choroidal point) and also constitutes the anterior wall of the temporal horn. 1, lateral orbital gyrus;
2, anterior orbital gyrus; 3, medial orbital gyrus; 4, rectus gyrus; 5, olfactory tract; 6, optic nerve;
7, amygdala; 8, internal carotid artery; 9, tuber cinereum and pituitary stalk; 10, parahippocampal
gyrus; 11, rhinal sulcus; 12, temporal horn cavity; 13, head of the hippocampus; 14, posterior
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perforated substance; 15, optic tract; 16, medial geniculate body; 17, trochlear nerve; 18, tail of
the hippocampus; 19, pineal gland; 20, fusiform gyrus; 21, collateral sulcus; 22, occipitotemporal
sulcus.
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FIGURE 27. Superior view of the right temporal horn. The right temporal lobe has been
disconnected from the rest of the brain: anteriorly from the limen insulae and from the putamen;
medially, from the thalamus through the choroidal fissure; posteriorly, from the fornix and tail of
the hippocampus; and superiorly, from the frontal and parietal opercula. The hippocampus occupies
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the medial part of the floor of the temporal horn and is divided into head, body, and tail. The tail
has an almost horizontal axis; the body of the hippocampus has an almost anteroposterior axis;
and anterior to the inferior choroidal point is the head of the hippocampus, which has an almost
horizontal axis. In this figure, the anterior disconnection has been performed at the level of the
globus pallidus (characterized by lenticulostriate arteries displayed in red). Note that the medial
end of the head of the hippocampus cannot be seen because it is hidden under the globus pallidus.
1, planum polare; 2, rhinal sulcus; 3, anterior segment of the uncus; 4, apex of the uncus; 5,
globus pallidus; 6, limen insulae; 7, head of the hippocampus; 8, inferior choroidal point; 9,
collateral eminence; 10, parahippocampal gyrus; 11, fimbria; 12, body of the hippocampus; 13,
Heschl’s gyrus; 14, middle transverse temporal gyrus; 15, tail of the hippocampus; 16, calcar avis;
17, bulb of the callosum; *, sylvian point (middle cerebral artery).
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FIGURE 28. Magnified view of Figure 27.
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FIGURE 29. Continuation of Figure 28. An additional axial cut has been performed under the globus
pallidus to display the amygdala. The head of the hippocampus still cannot be visualized in its full
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extent because it is still hidden by the amygdala, which continues superiorly as globus pallidus. 1,
rhinal sulcus; 2, limen insulae; 3, apex of the uncus; 4, semilunar gyrus and sulcus semiannularis;
5, amygdala; 6, posterior segment of the uncus; 7, medial wall of the temporal horn anterior to
inferior choroidal point (head of the hippocampus); 8, fornix (cut).
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FIGURE 30. Continuation of Figure 29. The amygdala above the head of the hippocampus has been
totally removed. The head of the hippocampus with its digitations is directed medially toward the
posterior segment of the uncus; lateral to the apex and anterior to the head of the hippocampus is
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the uncal recess. The uncal recess is the continuation of the collateral eminence, which turns
medially, following the head of the hippocampus, and it is the most anterior part of the temporal
horn cavity; hence, it has an anteromedial direction and it is related anteromedially to the anterior
wall of the temporal horn, namely, the amygdala, and anterolaterally to the limen insulae;
superiorly, it is still related to the amygdala; posteriorly, it is related to the head of the
hippocampus; medially, it is related to the apex of the uncus or even to the anterior segment when
the temporal horn cavity is dilated. The head of the hippocampus is the medial wall of the temporal
horn anterior to the inferior choroidal point; the choroidal fissure is the medial wall of the temporal
horn posterior to the inferior choroidal point. 1, rhinal sulcus; 2, amygdala; 3, semilunar gyrus; 4,
head of the hippocampus; 5, posterior segment of the uncus; 6, inferior choroidal point; *, uncal
recess.
Although the uncus is an extraventricular structure, it is closely related to the temporal horn
cavity and its contents. The head of the hippocampus with its digitations is directed medially toward
the posterior segment of the uncus; the uncinate gyrus is actually the external representation of
the hippocampal digitations (13).
Lateral to the apex and anterior to the head of the hippocampus is the uncal recess. The uncal
recess is actually the continuation of the collateral eminence, which turns medially, following the
head of the hippocampus, and is the most anterior part of the temporal horn cavity; it consequently
has an anteromedial direction and is related anteromedially to the anterior wall of the temporal
horn, namely, the amygdala, and anterolaterally to the limen insulae; superiorly, it is still related to
the amygdala; posteriorly, it is related to the head of the hippocampus; medially, it is related to the
apex of the uncus or even to the anterior segment when the temporal horn cavity is dilated (Figs.
27–30).
Roof of the temporal horn
The roof of the temporal horn is part of the temporal stem, and it comprises the retrolentiform
and sublentiform components of the internal capsule; the retrolentiform part is composed of the
parietopontine, occipitopontine, occipitocollicular, and occipitotectal fibers and also the posterior
thalamic radiation, which includes the optic radiation, and interconnections between the occipital
and parietal lobes and caudal parts of the thalamus (Figs. 31 and 32) (66, 68). The sublentiform part
of the internal capsule contains the temporopontine and parietopontine fibers: the acoustic
radiation from the medial geniculate body to the superior temporal and transverse temporal gyri,
and fibers connecting the thalamus with the temporal lobe and insula. The tapetum of the corpus
callosum along with the tail of the caudate nucleus are parts of the roof of the temporal horn as
well. From the neurosurgical viewpoint, the most important component of the roof of the temporal
horn is the optic radiation (8). There is no clear separation between the roof of the temporal horn
and the thalamus; because all fibers of the optic radiation come from the lateral geniculate body,
which belongs to the thalamus, it is reasonable to consider the roof of the temporal horn as a
lateral extension of the thalamus. This anatomic concept plays an important role when entry into
the temporal horn from its roof is intended (as in the transsylvian approach or in standard temporal
lobectomy). The roof of the temporal horn should not be removed too medially because of the risk
of damaging the thalamus (Fig. 33).
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FIGURE 31. Lateral view of the right hemisphere. An axial cut of the brain followed by the removal
of the lateral wall of the atrium and part of the lateral wall of the temporal horn has been
performed to display the relationship among the roof of the temporal horn, the components of the
internal capsule, and the lentiform nucleus. 1, splenium of the corpus callosum; 2, head of the
caudate nucleus; 3, thalamus; 4, genu of the internal capsule; 5, anterior limb of the internal
capsule; 6, posterior limb of the internal capsule; 7, calcar avis; 8, glomus (choroid plexus); 9,
retrolentiform part of the internal capsule; 10, lentiform nucleus; 11, collateral trigone; 12,
sublentiform part of the internal capsule and roof of the temporal horn.
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FIGURE 32. Magnified view of Figure 31.
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FIGURE 33. Basal view of the left hemisphere. The floor of the temporal horn along with the
posterior segment of the uncus and the parahippocampal and fusiform gyri have been removed to
display the roof of the temporal horn. The optic radiation is part of the roof of the temporal horn,
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and there is no clear separation between the roof of the temporal horn and the thalamus, since all
fibers of the optic radiation come from the lateral geniculate body (thalamus); the roof of the
temporal horn can be considered a lateral extension of the thalamus. The inferior choroidal point,
the inferior termination of the choroidal fissure, is located immediately behind the uncus, below and
slightly anterior to the lateral geniculate body of the thalamus, and it is just anterior to the site
where the anterior choroidal artery enters the temporal horn and where the inferior ventricular vein
exits the temporal horn to join the basal vein of Rosenthal. After arising from the supraclinoid
segment of the internal carotid artery, the anterior choroidal artery initially courses posteriorly,
superiorly, and medially in the carotid cistern, and then continues medial to the anteromedial
surface of the uncus to reach the optic tract superolateral to the posterior communicating artery; at
this point, it diverges from the posterior communicating artery and courses posteriorly, superiorly,
and laterally, under the optic tract, to enter the crural cistern between the superior part of the
posteromedial surface of the uncus and the crus cerebri; after passing the posterior edge of the
intralimbic gyrus, it enters the temporal horn of the lateral ventricle through the choroidal fissure.
1, internal carotid artery; 2, anterior cerebral artery; 3, anterior segment of the uncus; 4, optic
tract and oculomotor nerve; 5, basal vein (first or striate segment) and anterior choroidal artery
(cisternal segment); 6, amygdala; 7, peduncular vein and posterior perforated substance; 8, basal
vein (peduncular segment); 9, inferior choroidal point, inferior ventricular vein, and anterior
choroidal artery (plexal segment); 10, lateral geniculate body; 11, pulvinar of the thalamus; 12,
splenium of the corpus callosum; 13, vein of Galen; 14, lingual gyrus.
Choroidal fissure
The choroidal fissure is a cleft located between the thalamus and the fornix and is the site of
attachment of the choroid plexus in the lateral ventricle. The choroidal fissure is a C-shaped arc
that extends from the foramen of Monro through the body, atrium, and temporal horn of the lateral
ventricle (37). The inferior choroidal point, the inferior termination of the choroidal fissure, is
located immediately behind the uncus, below and slightly anterior to the lateral geniculate body of
the thalamus, and it is just anterior to the site where the anterior choroidal artery enters the
temporal horn and where the inferior ventricular vein exits the temporal horn to join the basal vein
of Rosenthal (Fig. 33). In the temporal horn, the choroidal fissure is located between the stria
terminalis of the thalamus superomedially and the fimbria inferolaterally; the choroid plexus is
attached to the thalamus and to the fimbria via the taenia fimbriae and the taenia choroidea, which
are actually the ependymal covering (Fig. 34). In the temporal lobe, the choroidal fissure is related
to the body and the tail of the hippocampus; the head of the hippocampus is related to the
posterior segment of the uncus and not to the choroidal fissure.
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FIGURE 34. Diagram displaying a coronal section through the right temporal horn and the
brainstem. The cavity of the temporal horn is shown in yellow, the ependymal covering is in green,
and the pia mater is in red. Note that the choroid plexus is covered by pia mater and ependyma.
The taenia choroidea and taenia fimbriae are ependymal covering that attaches the choroid plexus
to the thalamus and to the fimbria, respectively. 1, choroid plexus; 2, fimbria; 3, hippocampus; 4,
hippocampal sulcus (between the dentate gyrus superiorly and the parahippocampal gyrus
inferiorly); 5, brainstem; 6, occipitotemporal sulcus; 7, collateral sulcus; 8, parahippocampal
gyrus; 9, inferior temporal gyrus; 10, fusiform gyrus.
The choroidal fissure is the medial wall of the posterior two-thirds of the temporal horn, and it
is one of the most valuable anatomic landmarks that a neurosurgeon can count on during surgical
procedures. The choroidal fissure of the temporal horn is easily identified by following the choroid
plexus in the medial aspect of the temporal horn; all structures located laterally to the choroid
plexus belong to the temporal lobe and can be removed, and all structures located medially to the
choroidal fissure in the temporal horn belong to the thalamus and should not be harmed. Opening
the choroidal fissure in the temporal horn leads to the contents of the ambient cistern.
Entorhinal area
An important histological concept that plays a major role in neurosurgery, and especially in
epilepsy surgery, is the entorhinal area, which occupies approximately the anterior third of the
parahippocampal gyrus and the anteroinferior portion of the anterior segment of the uncus;
posteriorly, on the parahippocampal gyrus, it extends slightly behind the level of the posterior pole
of the uncus. The entorhinal area therefore forms a “shell” around the temporal amygdala (13). It is
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limited laterally by the rhinal sulcus anteriorly and the collateral sulcus posteriorly. The entorhinal
area is composed of the six-layered mesocortex, and it plays a major role as a relay for both
efferent and afferent connections between the hippocampus and the isocortical association cortex in
the temporal, parietal, and frontal lobes.
Vascular relationships: arterial
In this section, special attention will be directed to the arterial relationships of the uncus, owing
to its importance in neuroradiology and particularly in neurosurgical procedures involving the
amygdalohippocampal area. The arteries related to the uncus and to the mesial temporal region are
the internal carotid, posterior communicating, anterior choroidal, posterior cerebral, and middle
cerebral arteries.
Internal carotid artery
The internal carotid artery is divided into five segments, the cervical, petrous, cavernous,
clinoidal, and supraclinoidal segments; only the supraclinoidal segment is related to the uncus. The
supraclinoidal segment of the internal carotid artery exits from the dura mater (distal ring), which
forms the roof of the clinoidal segment, and then enters the intradural space on the medial side of
the anterior clinoidal process below the optic nerve and runs superiorly, posteriorly, and laterally
toward the anterior perforated substance (Fig. 35). It bifurcates in the area below the anterior
perforated substance at the medial end of the sylvian fissure into the anterior and middle cerebral
arteries (47). This segment is closely related to the anteromedial surface (anterior segment) of the
uncus (Fig. 36).
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FIGURE 35. Frontal view of the brain. A coronal cut has been performed at the level of the optic
chiasm to display the supraclinoid segment of the internal carotid artery and its branches. The
supraclinoid segment of the internal carotid artery exits from the dura and then enters the
intradural space on the medial side of the anterior clinoidal process below the optic nerve and runs
superiorly, posteriorly, and laterally toward the anterior perforated substance. It bifurcates in the
area below the anterior perforated substance at the medial end of the sylvian fissure into the
anterior and middle cerebral arteries. 1, cingulate gyrus; 2, corpus callosum and septum
pellucidum; 3, fornix; 4, thalamus; 5, genu of the internal capsule and thalamostriate vein; 6,
anterior commissure and column of the fornix; 7, M2 segment of the middle cerebral artery; 8,
limen insulae; 9, anterior cerebral artery; 10, lenticulostriate arteries; 11, M1 segment of the
middle cerebral artery; 12, internal carotid artery; 13, optic nerve; 14, anterior clinoid process.
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FIGURE 36. Basal view. The supraclinoid segment of the internal carotid artery is closely related to
the anteromedial surface of the uncus (anterior segment). After arising from the supraclinoidal
segment of the internal carotid artery, the posterior communicating artery courses posteromedially
below the optic tract and tuber cinereum, above the sella turcica and oculomotor nerve, close to
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the dura overlying the posterior clinoid process before piercing the Liliequist membrane of the
interpeduncular cistern to join the posterior cerebral artery. The posterior cerebral arteries are the
terminal branches of the basilar artery in the interpeduncular cistern and are divided into four
segments. The P1 extends from the basilar bifurcation to the posterior communicating artery. The
P2A extends from the posterior communicating artery to the posterior edge of the crus cerebri. The
P2P extends from the posterior edge of the crus cerebri to the posterior margin of the midbrain.
The P3 begins at the posterior midbrain, runs within the quadrigeminal cistern, and ends at the
anterior limit of the calcarine fissure. The P4 is the cortical segment of the posterior cerebral artery.
1, middle cerebral artery; 2, internal carotid artery; 3, anterior cerebral artery; 4, anterior
choroidal artery; 5, posterior communicating artery; 6, tuber cinereum and P1 segment of the
posterior cerebral artery; 7, anterior segment, apex, and posterior segment of the uncus; 8,
oculomotor nerve and P2A segment of the posterior cerebral artery; 9, P2P segment of the
posterior cerebral artery; 10, parahippocampal gyrus; 11, P3 segment of the posterior cerebral
artery; *, inferior temporal arteries.
Posterior communicating artery
The posterior communicating artery arises from the posteromedial or posterior or posterolateral
wall of the supraclinoidal segment of the internal carotid artery (47) and runs posteromedially below
the tuber cinereum above the sella turcica and oculomotor nerve, close to the dura overlying the
posterior clinoid process, before piercing the Liliequist membrane of the interpeduncular cistern to
join the posterior cerebral artery. It has an entirely cisternal trajectory; however, it is encased in a
sleeve of arachnoid membrane (Figs. 36 and 37). The posterior communicating artery is not truly in
contact with any segment of the uncus, and its course is variable; in the present study, the
posterior communicating artery is mostly related at a certain distance to the anteromedial surface
of the uncus and to the uncal notch.
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FIGURE 37. Magnified view of Figure 36. 1, internal carotid artery; 2, posterior communicating
artery; 3, anterior choroidal artery; 4, P1 segment of the posterior cerebral artery; 5, P2 segment
of the posterior cerebral artery; 6, uncus; 7, P3 segment of the posterior cerebral artery; 8, vein of
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Galen; 9, P4 segment of the posterior cerebral artery.
Anterior choroidal artery
The anterior choroidal artery arises distal to the posterior communicating artery from the
posterolateral wall of the internal carotid artery in most cases (14, 22, 35, 46, 54, 58, 59, 64, 65). The
anterior choroidal artery initially runs posteriorly, superiorly, and medially behind the internal
carotid artery in the carotid cistern, medial to the anteromedial surface of the uncus to reach the
optic tract superolateral to the posterior communicating artery; at this point, it diverges from the
posterior communicating artery and runs posteriorly, superiorly, and laterally under the optic tract
to enter the crural cistern between the superior part of the posteromedial surface of the uncus and
the crus cerebri; after passing the posterior edge of the intralimbic gyrus, it enters the temporal
horn of the lateral ventricle (Figs. 33, 42, and 46).
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FIGURE 42. Continuation of Figure 41. The optic tract and the thalamus have been removed. The
basal vein and the anterior choroidal artery can be visualized running in the crural cistern under the
optic tract. The lateral posterior choroidal arteries, which arise from the posterior cerebral artery,
course through the choroidal fissure to supply the choroid plexus. The configuration of the
trajectory of the anterior choroidal artery depicts precisely the shape of the uncus. 1, bulb of the
callosum; 2, calcar avis; 3, vein of Galen, internal cerebral veins, and pineal gland; 4, glomus
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(choroid plexus); 5, tectal area of the midbrain; 6, P2P segment of the posterior cerebral artery; 7,
parahippocampal gyrus; 8, body of the hippocampus and lateral posterior choroidal arteries; 9,
inferior ventricular vein and peduncular segment of the basal vein; 10, peduncular vein and P1
segment of the posterior cerebral artery; 11, P2A segment of the posterior cerebral artery and
cisternal segment of the anterior choroidal artery; 12, posterior communicating artery; 13, head of
the hippocampus; 14, limen insulae; 15, M1 segment of the middle cerebral artery; 16, M2
segment of the middle cerebral artery; 17, olfactory tract; *, entry site of the anterior choroidal
artery in the temporal horn.
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FIGURE 46. Basal view of the left hemisphere. The posterior cerebral artery and its branches along
with the parahippocampal gyrus and the floor of the temporal horn have been removed to show the
roof of the temporal horn (part of the choroid plexus of the temporal horn has been removed). The
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cisternal segment of the anterior choroidal artery arises from the supraclinoid segment of the
internal carotid artery and courses posteriorly, first medially and then laterally, to reach the crural
cistern between the superior part of the posteromedial surface of the uncus and the crus cerebri
under the optic tract; the anterior choroidal artery thereupon follows the optic tract up to its entry
into the temporal horn through the inferior choroidal point of the choroidal fissure to continue as
the plexal segment. The inferior ventricular vein arises in the posterolateral part of the roof of the
temporal horn and courses anteromedially to exit the temporal horn just behind the inferior
choroidal point to join the basal vein at the most lateral point of the course of the basal vein around
the crus cerebri near the lateral geniculate body. 1, internal carotid artery; 2, optic tract; 3,
anterior choroidal artery (cisternal segment) and striate segment of the basal vein; 4, peduncular
vein; 5, peduncular segment of the basal vein; 6, inferior choroidal point; 7, inferior ventricular
vein; 8, lateral geniculate body; 9, anterior choroidal artery (plexal segment); 10, medial
geniculate body and lateral mesencephalic vein; 11, pulvinar of the thalamus; 12, posterior
mesencephalic segment of the basal vein; 13, posterior longitudinal hippocampal and internal
occipital veins; 14, internal cerebral vein; 15, vein of Galen.
During its trajectory from the internal carotid artery to the temporal horn, the anterior
choroidal artery is related, respectively, to the carotid and crural cisterns; the anteromedial and
posteromedial surfaces of the uncus are the lateral limits of the carotid and the crural cisterns,
respectively. The height of the origin of the anterior choroidal artery depends on the height of the
bifurcation of the internal carotid artery; however, the entry point of the anterior choroidal artery in
the choroidal fissure is constant. The crural cistern therefore is defined superiorly by the optic tract,
medially by the upper portion of the crus cerebri, and laterally by the upper portion of the
posteromedial surface of the uncus (19).
Posterior cerebral artery
The posterior cerebral arteries arise as the terminal branches of the basilar artery in the
interpeduncular cistern and are divided into four segments (Figs. 36, 37, 38, and 45) (30, 31, 72, 77). P1
extends from the basilar bifurcation to the posterior communicating artery; P2A extends from the
posterior communicating artery to the posterior edge of the crus cerebri; P2P extends from the
posterior edge of the crus cerebri to the posterior margin of the midbrain; P3 begins at the
posterior midbrain, runs within the quadrigeminal cistern, and ends at the anterior limit of the
calcarine fissure; and P4 is the cortical segment of the posterior cerebral artery.
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FIGURE 38. Inferomedial view of the right hemisphere. 1, internal carotid artery; 2, posterior
communicating artery; 3, P1 segment of the posterior cerebral artery; 4, middle cerebral artery; 5,
P2 segment; 6, beginning of the P3 segment; 7, beginning of the P4 segment; 8, inferior temporal
arteries from the posterior cerebral artery and parahippocampal gyrus; 9, isthmus of the cingulate
gyrus; 10, parieto-occipital sulcus; 11, cuneus; 12, calcarine sulcus and lingual gyrus.
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FIGURE 45. Posterior continuation of Figure 44. The cuneus and the superior part of the calcar avis
have been removed to display the calcarine sulcus protruding toward the medial wall of the atrium.
The relationship between the four segments of the posterior cerebral artery and the brainstem and
the mesial temporal lobe can be seen. In this specimen, the basal vein drains into the lateral
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mesencephalic vein and then to the superior petrosal sinus instead of the galenic system. 1,
parieto-occipital artery; 2, lingual gyrus; 3, calcarine artery; 4, calcar avis; 5, trochlear nerve; 6,
parahippocampal gyrus; 7, dentate gyrus; 8, fornix; 9, anastomosis between branches from the
anterior choroidal artery and lateral posterior choroidal arteries in the temporal horn; 10, basal
vein; 11, digitations of the head of the hippocampus.
The P1 segment of the posterior cerebral artery is entirely cisternal and is not related to the
uncus. The P2A segment passes from the interpeduncular cistern to the ambient cistern, turning
around the crus cerebri, and is related to the posteromedial segment of the uncus. In the present
study, the posterior cerebral artery is mostly related to the inferior portion of the posteromedial
segment of the uncus, whereas the anterior choroidal artery is mostly related to the superior
portion of the posteromedial surface of the uncus.
The main branches of the P1 segment are the posterior thalamoperforating arteries; the medial
posterior choroidal, the short and long circumflex, the hippocampal, and the lateral posterior
choroidal arteries usually arise from the P2 segment (Figs. 39 and 40). The hippocampal formation is
supplied by the hippocampal arteries, which enter the hippocampus by penetrating the dentate
gyrus, the fimbriodentate sulcus, and the hippocampal sulcus. They can originate from the anterior
choroidal artery, the main trunk of the posterior cerebral artery (Uchimura artery), and the inferior
temporal, lateral posterior choroidal, and splenial branches of the posterior cerebral artery (9, 28,
29, 36).
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FIGURE 39. Basal view. The right parahippocampal gyrus has been removed from the dentate
gyrus and fimbria, and the temporal horn has been entered. The hippocampal arteries arise either
from the anterior choroidal artery or posterior cerebral artery and course through the hippocampal
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notch or hippocampal sulcus or fimbrodentate sulcus to supply the hippocampal formation. Unlike
the hippocampal arteries, the anterior choroidal and lateral posterior choroidal arteries course
through the choroidal fissure (between the fornix and the thalamus) to supply the choroid plexus.
1, internal carotid artery; 2, middle cerebral artery; 3, anterior choroidal artery; 4, posterior
communicating artery; 5, P2A segment of the posterior cerebral artery; 6, inferior surface of the
posterior segment of the uncus; 7, dentate gyrus; 8, P2P segment of the posterior cerebral artery;
9, fimbria; 10, lateral posterior choroidal artery; 11, glomus; *, hippocampal arteries; **, pulvinar
of the thalamus.
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FIGURE 40. Magnified view of Figure 39. 1, anterior choroidal artery; 2, inferior surface of the
posterior segment of the uncus; 3, P2A segment of the posterior cerebral artery; 4, basal vein; 5,
dentate gyrus and fimbria; 6, anterior and posterior longitudinal hippocampal veins; 7, pulvinar of
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the thalamus; 8, P2P segment of the posterior cerebral artery; *, hippocampal arteries; **, lateral
posterior choroidal artery.
Unlike the hippocampal arteries, which penetrate the hippocampal formation via the dentate
gyrus, the fimbriodentate sulcus, and the hippocampal sulcus, the lateral posterior choroidal
arteries enter the temporal horn via the choroidal fissure; this is also an important intraoperative
vascular landmark (Figs. 39 and 40). The posterior cerebral artery is intimately related to the
hippocampal sulcus; the anterior portion of the parahippocampal gyrus lies immediately lateral to
the posterior cerebral artery on the anteroposterior view of the vertebrobasilar angiogram, whereas
the midbrain lies immediately medial to the posterior cerebral artery.
Understanding of the course and branching pattern of these arteries implies an understanding
of their spatial arrangement in their respective cisterns. Understanding of these cisterns, in turn,
will automatically lead to understanding of the neural structures that constitute the boundaries of
these cisterns. The complex relationships between these arteries, their cisterns, and the neural
structures that constitute the boundaries of these cisterns are demonstrated in Figures 41 to 45.
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FIGURE 41. Anterosuperior view. The left frontal and parietal opercula have been removed to
display the temporal horn and the uncus. An axial cut has been made on the brainstem at the optic
tract, which is the roof of the crural cistern. 1, calcar avis (medial wall of the atrium); 2, Heschl’s
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gyrus and branches of the middle cerebral artery; 3, thalamus; 4, lateral geniculate body; 5, optic
tract; 6, floor of the third ventricle (mamillary bodies); 7, anterior choroidal artery (under the optic
tract and medial to the uncus); 8, head of the hippocampus and inferior choroidal point; 9, superior
sagittal sinus; 10, internal carotid artery; 11, anterior cerebral artery; 12, optic nerve; 13, middle
cerebral artery (M1 segment).
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FIGURE 43. Magnified view of Figure 42, displaying the origin and trajectory of the posterior
communicating and anterior choroidal arteries, as well as the course of the basal vein. The anterior
choroidal artery and the basal vein run in the crural cistern under the optic tract and between the
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crus cerebri and the posterior segment of the uncus. The proximal portion of the M1 segment of the
middle cerebral artery and the internal carotid artery are closely related to the anterior segment of
the uncus. 1, tegmentum of the midbrain; 2, substantia nigra; 3, inferior ventricular and basal
veins; 4, crus cerebri; 5, entry site of the anterior choroidal artery in the temporal horn behind the
posterior segment of the uncus; 6, peduncular vein and P1 segment of the posterior cerebral
artery; 7, P2A segment of the posterior cerebral artery and cisternal segment of the anterior
choroidal artery; 8, posterior segment of the uncus; 9, oculomotor nerve; 10, apex of the uncus;
11, head of the hippocampus; 12, posterior communicating artery; 13, anterior segment of the
uncus; 14, semilunar gyrus; 15, origin of the anterior choroidal artery from the internal carotid
artery; 16, A1 segment of the anterior cerebral artery; 17, M1 segment of the middle cerebral
artery; 18, optic nerve.
FIGURE 44. Continuation of Figure 43. The anterior choroidal and posterior cerebral arteries have
been retracted toward the posterior segment of the uncus to display the arachnoid membrane,
which separates the supratentorial compartment from the infratentorial compartment of the
ambient cistern. The transition between the anterior pontomesencephalic and lateral
pontomesencephalic segments of the superior cerebellar artery can be seen through the arachnoid
membrane. 1, vein of Galen; 2, medial posterior choroidal artery; 3, cerebellomesencephalic
segment of the superior cerebellar artery and free edge of the tentorium; 4, posterior cerebral
artery and parahippocampal gyrus; 5, fimbria, dentate gyrus, and lateral posterior choroidal
arteries; 6, basal vein draining toward the lateral mesencephalic vein; 7, inferior ventricular vein;
8, superior cerebellar artery and free edge of the tentorium; 9, oculomotor nerve, P1 segment of
the posterior cerebral artery, and peduncular vein; 10, optic tract; 11, head of the hippocampus; *,
hippocampal artery; **, posterior perforated substance.
Before describing the boundaries of the crural and ambient cisterns, it is worthwhile to mention
the external features of the mesencephalon that are frequently misnamed: the midbrain or
mesencephalon is divided into two halves, the right and left cerebral peduncles, by a sagittal plane;
the cerebral peduncle is demarcated into an anterior crus cerebri and a posterior tegmental part by
the substantia nigra (Fig. 18). The area of the tegmental part of the midbrain that is posterior to an
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oblique coronal plane that passes just in front of the cerebral aqueduct is the tectum, which
includes the pretectal area and the quadrigeminal plate or corpora quadrigemina (66, 68). The crus
cerebri, which is frequently misnamed as the cerebral peduncle, is actually only the anterior part of
the cerebral peduncle, which includes the crus cerebri and the tegmentum.
There are still some controversies regarding the boundaries of the crural and ambient cisterns.
The crural cistern has been named as the space limited laterally by the uncus, medially by the crus
cerebri, and superiorly by the optic tract (26); it connects the carotid cistern anteriorly to the
ambient cistern posteriorly. Its contents include the basal vein, the cisternal segment of the
anterior choroidal artery, and the P2A segments of the posterior cerebral artery. Other authors
think that the crural cistern (19, 73, 76) is limited superiorly by the optic tract, medially by the crus
cerebri, and laterally by the uncus and is located superiorly to the initial segment of the ambient
cistern that runs below it. The contents of the crural cistern are constituted by the anterior
choroidal artery and the basal vein (Fig. 46). The P2A segment of the posterior cerebral artery
passes through the initial segment of the ambient cistern. The crural cistern is therefore limited
superiorly by the optic tract (Fig. 41), and after its removal, the boundaries of the crural cistern and
the initial segment of the ambient cistern can be visualized; the crural cistern and the initial
segment of the ambient cistern actually share the same lateral and medial limits, respectively, the
posteromedial surface of the uncus and the crus cerebri, yet at different heights: the crural cistern
is located superiorly to the ambient cistern; whereas the crural cistern ends with the entry of the
anterior choroidal artery into the temporal horn, the ambient cistern continues posteriorly between
the parahippocampal gyrus and the brainstem (Figs. 42 - 45) (3, 4, 25).
Middle cerebral artery
The middle cerebral artery arises from the bifurcation of the internal carotid artery below the
anterior perforated substance and it is divided into four segments (11, 17, 27, 62): M1, from the
carotid bifurcation to the limen insulae; M2, all branches related to the insula, from the limen
insulae to the opercula of the temporal, frontal, or parietal lobes; M3, all branches related to the
opercula of the temporal, frontal or parietal lobes; and M4, the cortical branches of the middle
cerebral artery, after exiting from the sylvian fissure.
Only the M1 segment is related to the mesial temporal lobe. Because of differences in
topographical anatomy, the M1 segment can be divided into a proximal and a distal half. The
proximal half of the M1 segment is related superiorly to the anterior perforated substance,
posteriorly to the semilunar gyrus and the temporal amygdala, and inferiorly to the entorhinal area
of the uncus (Figs. 5 and 54) (HT Wen, AL Rhoton Jr, E de Oliveira, in preparation).
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FIGURE 54. Anteroposterior view as in angiography. The frontoparietal opercula, the basal ganglia,
and the cuneus have been removed on the left hemisphere. The uncus can be characterized
angiographically either by arteries or veins. The internal carotid, anterior choroidal, and posterior
cerebral arteries in addition to the basal vein can be used for this purpose. The cisternal segment of
the anterior choroidal artery along with the striate and peduncular segments of the basal vein
delineate the silhouette of the apex and the posterior segment of the uncus. 1, olfactory tract; 2,
anterior cerebral artery; 3, genu of the middle cerebral artery; 4, limen insulae; 5, optic nerve and
internal carotid artery; 6, entorhinal area of the uncus; 7, M1 segment of the middle cerebral
artery; 8, semilunar gyrus; 9, posterior communicating artery; 10, P1 segment of the posterior
cerebral artery and peduncular vein; 11, head of the hippocampus and choroid plexus of the
temporal horn; 12, cisternal segment of the anterior choroidal artery and peduncular segment of
the basal vein; 13, plexal segment of the anterior choroidal artery anastomosing with branches of
the lateral posterior choroidal artery; 14, P2P segment of the posterior cerebral artery and
parahippocampal gyrus; 15, vein of Galen; 16, sylvian point and Heschl’s gyrus; 17, calcarine
artery; 18, parieto-occipital artery.
Arterial relationship of the uncus
The relationships between the uncus and the above-mentioned arteries and its angiographic
correlation are displayed in Figures 47 to 55 (18). The supraclinoid segment of the internal carotid
artery is located at the most anterior aspect of the anterior segment of the uncus. The posterior
communicating artery is not truly in contact with any surface of the uncus; however, in the medial
view in this study, we can see that it is mostly related to the tentorial notch.
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FIGURE 47. Medial view of the right hemisphere. Part of the anterior wall and the floor of the third
ventricle have been removed. The perforating arteries arise from anterior cerebral, middle cerebral,
internal carotid and the anterior choroidal arteries and run superiorly and posteriorly toward the
anterior perforated substance. 1, foramen of Monro and column of the fornix; 2, thalamus; 3,
aqueduct; 4, mamillary body; 5, crus cerebri and posterior perforated substance; 6, internal carotid
artery.
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FIGURE 48. Medial view. The crus cerebri and the tegmentum of the midbrain have been removed.
The P2A segment of the posterior cerebral artery is related to the inferior portion of the
posteromedial surface of the uncus. The relationship between the anteromedial surface of the
uncus and the initial portion of the cisternal segment of the anterior choroidal artery is variable,
depending on the height of the origin of the anterior choroidal artery from the internal carotid
artery; the distal portion of the cisternal segment of the anterior choroidal artery is always related
to the upper portion of the posteromedial surface of the uncus, as it enters the temporal horn
through the choroidal fissure that is located posterior to the uncus, at its top. 1, corpus callosum;
2, column of the fornix and anterior commissure; 3, foramen of Monro; 4, thalamus; 5, aqueduct;
6, anterior cerebral artery; 7, M1 segment of the middle cerebral artery; 8, initial portion of the
cisternal segment of the anterior choroidal artery (over the anteromedial surface of the uncus) and
its perforators; 9, distal portion of the cisternal segment of the anterior choroidal artery (on the
upper portion of the posteromedial surface of the uncus) entering the temporal horn; 10, internal
carotid artery; 11, posterior communicating artery; 12, P2A segment of the posterior cerebral
artery; 13, P1 segment of the posterior cerebral artery; 14, pons; 15, fourth ventricle; 16, rhinal
sulcus.
FIGURE 49. Magnified view of Figure 48. Note that, in this view, the M1 segment of the middle
cerebral artery is almost parallel to our view; this arrangement along with the superimposition of
the vessels explains why visualization of this segment on the lateral view of the angiogram is
difficult. 1, anterior cerebral artery; 2, M1 segment of the middle cerebral artery; 3, semilunar
gyrus; 4, anterior choroidal artery; 5, entry site of the anterior choroidal artery in the temporal
horn; 6, posteromedial surface of the uncus; 7, P2P segment of the posterior cerebral artery; 8,
ambient gyrus; 9, P2A segment of the posterior cerebral artery; 10, internal carotid artery; 11,
posterior communicating artery; 12, parahippocampal gyrus; 13, P1 segment of the posterior
cerebral artery; 14, fusiform gyrus; 15, pons.
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FIGURE 50. Medial view. The brainstem has been removed. Note that the internal carotid artery,
the proximal portion of the cisternal segment of the anterior choroidal artery, and the M1 segment
of the middle cerebral artery are related to the anterior segment of the uncus, whereas the P2A
segment of the posterior cerebral artery is related to the inferior portion of the posteromedial
surface of the posterior segment of the uncus, and the distal portion of the anterior choroidal artery
is related to the upper portion of the posteromedial surface of the uncus. 1, isthmus of the
cingulate gyrus; 2, distal portion of the P3 segment of the posterior cerebral artery; 3, initial
portion of the P3 segment of the posterior cerebral artery; 4, inferior temporal arteries 5,
parahippocampal gyrus; 6, fusiform gyrus; 7, rhinal sulcus; *, P2P segment of the posterior
cerebral artery.
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FIGURE 51. Angiographic correlation of Figure 50, lateral view. The uncus and the parahippocampal
gyrus can be characterized angiographically by following the internal carotid, middle cerebral,
posterior communicating, anterior choroidal, and posterior cerebral arteries. 1, proximal portion of
the cisternal segment of the anterior choroidal artery; 2, distal portion of the cisternal segment of
the anterior choroidal artery; 3, superimposition of M1, A1, and carotid bifurcation; 4, P2A segment
of the posterior cerebral artery; 5, posterior communicating artery; 6, internal carotid artery; 7, P1
segment of the posterior cerebral artery; 8, ophthalmic artery; 9, basilar artery; *, entry site of the
anterior choroidal artery in the temporal horn.
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FIGURE 52. Continuation of Figure 50. The posterior communicating and posterior cerebral arteries
have been removed to display the relationship between the cisternal segment of the anterior
choroidal artery and the uncus. 1, lingual gyrus; 2, parahippocampal gyrus; 3, apex of the uncus;
4, posteromedial surface of the uncus; 5, anteromedial surface of the uncus and anterior choroidal
artery; 6, uncal notch; 7, tentorial notch; 8, fusiform gyrus; *, entry site of the anterior choroidal
artery in the temporal horn.
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FIGURE 53. The relationship between the P2A segment of the posterior cerebral artery and the
posteromedial surface of the uncus is displayed in b to d. The relationship between the cisternal
segment of the anterior choroidal artery and the anteromedial surface of the uncus is displayed in e
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to g. The relationship between the cisternal segment of the anterior choroidal artery and the
posteromedial surface of the uncus is displayed in h to j. a, medial view of the uncus and the
anterior portion of the parahippocampal gyrus. b, in 88% of the specimens, the P2A segment of the
posterior cerebral artery passes at the level of the uncal notch. c, in 8% of the cases, the P2A
segment of the posterior cerebral artery passes above the uncal notch. d, in 4% of the cases, the
P2A segment of the posterior cerebral artery passes below the uncal notch. e, in 68% of the cases,
the proximal half of the cisternal segment of the anterior choroidal artery is related to the upper
third of the anteromedial surface of the uncus. f, in 10% of the cases, the proximal half of the
cisternal segment of the anterior choroidal artery is related to the middle third of the anteromedial
surface of the uncus. g, in 22% of the cases, the proximal half of the cisternal segment of the
anterior choroidal artery is related to the inferior third of the anteromedial surface of the uncus. h,
in 86% of the cases, the distal half of the cisternal segment of the anterior choroidal artery is
related to the upper third of the posteromedial surface of the uncus. i, in 2% of the cases, the
distal half of the cisternal segment of the anterior choroidal artery is related to the middle third of
the posteromedial surface of the uncus. j, in 12% of the cases, the distal half of the cisternal
segment of the anterior choroidal artery is related to the inferior third of the posteromedial surface
of the uncus.
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FIGURE 55. Anteroposterior view. The uncus can be characterized angiographically by the internal
carotid artery, the proximal portion of the M1 segment of the middle cerebral artery, the cisternal
segment of the anterior choroidal artery, and the P2A segment of the posterior cerebral artery. 1,
internal carotid artery; 2, posterior communicating artery; 3, M1 segment of the middle cerebral
artery; 4, A1 segment of the anterior cerebral artery and P1 segment of the posterior cerebral
artery (superimposed); 5, genu of the middle cerebral artery; 6, P2A segment of the posterior
cerebral artery (superimposed in part with the cisternal segment of the anterior choroidal artery);
7, M2 segment of the middle cerebral artery; 8, calcarine artery.
The anterior choroidal artery arises from the internal carotid artery in the carotid cistern, and
initially it is closely related to the anterior segment of the uncus at a variable height (the height of
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its origin depends on the height of the bifurcation of the internal carotid artery). It then runs
posteriorly, superiorly, and laterally in the crural cistern on the upper part of the posteromedial
surface of the uncus to finally enter the choroidal fissure close to the inferior choroidal point. It is
important to emphasize that not only is the inferior choroidal point the posterior limit of the uncus,
but its height also corresponds to the top of the uncus; in other words, the entire uncus is situated
ahead of and below the inferior choroidal point.
The relationship of the anterior choroidal artery to the uncus was studied in 52 hemispheres,
and its variations are shown in Figure 53. The P2A segment of the posterior cerebral artery passes at
the level of the uncal notch in 88% of the cases; the proximal half of the cisternal segment of the
anterior choroidal artery is related to the upper third of the anteromedial surface of the uncus in
68% of the cases, and the distal half of the cisternal segment of the anterior choroidal artery is
related to the upper third of the posteromedial surface of the uncus in 86% of the cases. The P2A
segment of the posterior cerebral artery, which originates in the interpeduncular cistern, runs
laterally and then posteriorly around the crus cerebri in the ambient cistern and is related to the
inferior portion of the posteromedial surface of the uncus, unlike the anterior choroidal artery,
which is related to the upper portion of the posteromedial surface of the uncus (Figs. 48 - 51).
The M1 segment of the middle cerebral artery in a medial view is hardly seen because of its
almost parallel course to our view. When the M1 segment presents a straight course, most of the
uncus is located posteriorly to it (Figs. 49 and 50); when the M1 segment is tortuous and closer to the
semilunar gyrus, the entorhinal area of the uncus becomes anterior and inferior to the M1 (Fig. 54).
The angiographic characterization of the uncus in the medial view can be seen in Figure 52. The
angiographic characterization of the uncus in the anteroposterior view is displayed in Figures 54 and
55.
An important neural structure that is intimately related to the uncus is the oculomotor nerve.
The oculomotor nerve, after exiting from the interpeduncular fossa, runs laterally, anteriorly, and
inferiorly to pierce the posterior portion of the roof of the cavernous sinus. It is related laterally to
the inferior portion of the apex of the uncus; just before piercing the roof of the cavernous sinus, it
is located below the anterior segment of the uncus (Figs. 56 - 58).
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FIGURE 56. Medial view. A midsagittal section has been performed. 1, anterior cerebral artery and
corpus callosum; 2, septum pellucidum; 3, fornix; 4, internal cerebral vein and medial posterior
choroidal artery; 5, massa intermedia; 6, lamina terminalis; 7, optic and infundibular recesses; 8,
posterior cerebral artery (above the third nerve); 9, crus cerebri; 10, superior cerebellar artery;
11, optic nerve; 12, oculomotor nerve and the uncus; 13, ophthalmic artery and supraclinoid
segment of the internal carotid artery; 14, pons; 15, pituitary gland and its stalk; 16,
intracavernous segment of the internal carotid artery; 17, basilar artery; 18, fourth ventricle.
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FIGURE 57. Continuation of Figure 56. The optic nerve, the anterior wall, and the floor of the third
ventricle have been removed to display the relationship between the oculomotor nerve and the
uncus. 1, internal carotid artery; 2, semilunar gyrus and cisternal segment of the anterior choroidal
artery; 3, entorhinal area of the uncus; 4, oculomotor nerve and apex of the uncus; 5, posterior
perforated substance; 6, dural ring, ophthalmic artery, and optic nerve (cut); 7, basilar artery and
free edge of the tentorium; 8, intracavernous carotid artery; 9, pituitary gland and stalk (cut).
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FIGURE 58. Magnified view of Figure 57. 1, A1 segment of the anterior cerebral artery (cut); 2,
semilunar gyrus and anterior choroidal artery; 3, posterior cerebral artery; 4, crus cerebri; 5,
supraclinoid segment of the internal carotid artery; 6, origin of the posterior communicating artery
(cut); 7, entorhinal area of the uncus; 8, oculomotor nerve and apex of the uncus; 9, superior
cerebellar artery; 10, optic nerve; 11, ophthalmic artery and dural ring; 12, intracavernous carotid
artery; 13, pituitary gland; 14, dorsum sellae and tentorium; 15, basilar artery.
Vascular relationships: venous
The veins of the mesial temporal region drain predominantly to the basal vein of Rosenthal; a
detailed anatomic description has been reported in the senior author’s earlier publication (44), and
the radiological aspect of the basal vein of Rosenthal has been brilliantly presented by Huang (21,
50).
In this article, the microsurgical anatomy of the veins draining the mesial temporal region will
be reviewed very briefly, with special attention directed to the anatomy and the angiographic
correlation of the basal vein of Rosenthal itself.
The deep venous system of the brain is divided into a ventricular group, composed of the veins
converging on the walls of the lateral ventricles, and a cisternal group, which includes the veins
draining the walls of the basal cisterns. In the mesial temporal region, both ventricular and
cisternal groups drain into the basal vein of the Rosenthal. The cisternal group in the mesial
temporal region is represented by the basal vein of Rosenthal, the anterior, middle, and posterior
temporal cortical veins, and the anterior longitudinal hippocampal, anterior hippocampal, lateral
mesencephalic, posterior mesencephalic, and posterior longitudinal hippocampal veins.
The basal vein of Rosenthal is the main venous channel that drains the mesial temporal region.
The basal vein originates below the anterior perforated substance by the union of the deep middle
cerebral, inferior striate, olfactory, fronto-orbital, and anterior cerebral veins, and it usually drains
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into the vein of Galen after passing around the midbrain (Fig. 59. The basal vein is divided into three
segments. The first, anterior or striate segment, originates from the junction of the anterior
cerebral, inferior striate, olfactory, fronto-orbital, and deep middle cerebral veins under the anterior
perforated substance and runs posteriorly under the optic tract, medially and inferiorly to the
anterior portion of the crus cerebri. This point corresponds to the most medial part in the course of
the basal vein (before its termination into the vein of Galen), and it usually also corresponds to the
most inferior part in its course. This point also denotes laterally the location of the apex of the
uncus (Fig. 60). The main tributaries of the first or striate segment of the basal vein are the
fronto-orbital, olfactory, inferior striate, anterior cerebral, deep middle cerebral, and anterior
pericallosal veins.
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FIGURE 59. Basal view of the basal vein and its tributaries. The parahippocampal gyri on both sides
have been removed; the floor of the temporal horn on the left hemisphere has also been removed.
The uncus and the fimbria on the right hemisphere were left intact. The basal vein is divided into
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three segments: the first, anterior or striate segment of the basal vein, originates from the junction
of the anterior cerebral, inferior striate, olfactory, fronto-orbital, and deep middle cerebral veins
under the anterior perforated substance; it then runs posteriorly and medially, under the optic
tract, to the anterior portion of the crus cerebri, depicting the location of the apex of the uncus. The
main tributaries of the first or striate segment of the basal vein are fronto-orbital, olfactory, inferior
striate, anterior cerebral, deep middle cerebral, and anterior pericallosal veins. The anterior
peduncular segment starts from the site where the peduncular vein joins the basal vein, and it runs
laterally between the upper part of the posteromedial surface of the uncus and the upper part of
the crus cerebri, under the optic tract, to reach the most lateral part of the crus cerebri, which
corresponds to the most lateral point of the vein as it turns around the peduncle, and it usually is
where the inferior ventricular vein joins the basal vein; after this point, the posterior peduncular
segment turns medially, superiorly, and posteriorly to the plane of the lateral mesencephalic
sulcus, behind the crus cerebri to constitute the posterior mesencephalic segment. The main
tributaries of the second or peduncular segment are the peduncular or interpeduncular vein and the
inferior ventricular, inferior choroidal, hippocampal, and anterior hippocampal veins. The third,
posterior or posterior mesencephalic, segment starts at the lateral mesencephalic sulcus, then runs
medially, superiorly, and posteriorly under the pulvinar of the thalamus to penetrate the
quadrigeminal cistern and generally to drain into the vein of Galen. The main tributaries of the third
or posterior mesencephalic segment are the lateral mesencephalic vein and the posterior thalamic,
posterior longitudinal hippocampal, medial temporal, and medial occipital veins. 1, olfactory vein;
2, fronto-orbital vein; 3, deep middle cerebral vein; 4, inferior striate vein; 5, anterior cerebral
vein; 6, optic tract; 7, striate segment; 8, apex of the uncus; 9, peduncular vein; 10, anterior
peduncular segment; 11, inferior surface of the posterior segment of the uncus; 12, oculomotor
nerve; 13, inferior ventricular vein; 14, dentate gyrus and fimbria; 15, lateral mesencephalic vein;
16, lateral geniculate body; 17, pulvinar of the thalamus; 18, posterior mesencephalic segment;
19, tectal area of the midbrain; 20, posterior longitudinal hippocampal vein; 21, vein of Galen; 22,
internal occipital vein; *, lateral mesencephalic sulcus.
FIGURE 60. Basal view. 1, deep middle cerebral vein and limen insulae; 2, olfactory vein; 3,
anterior pericallosal vein; 4, fronto-orbital vein; 5, semilunar gyrus; 6, striate segment of the basal
vein; 7, oculomotor nerve; 8, optic chiasm; 9, apex of the uncus; 10, peduncular vein; 11, anterior
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peduncular segment of the basal vein; 12, uncal vein; 13, inferior ventricular vein; 14, crus
cerebri; *, anterior cerebral vein.
The second, middle or peduncular segment, starts from this most medial point in the course of
the basal vein, which usually corresponds to the site where the peduncular vein joins the basal
vein. The second segment runs laterally between the upper part of the posteromedial surface of the
uncus and the upper part of the crus cerebri, under the optic tract, to reach the most lateral part of
the crus cerebri, which corresponds to the most lateral point of the vein as it turns around the crus
cerebri, and it is usually where the inferior ventricular vein joins the basal vein. This is called the
anterior peduncular segment by Huang and Wolf (21); it then turns medially, superiorly, and
posteriorly to the plane of the lateral mesencephalic sulcus, behind the crus cerebri, to constitute
the posterior peduncular segment (Fig. 60) (21). The main tributaries of the second or peduncular
segment are the peduncular or interpeduncular vein, inferior ventricular, inferior choroidal,
hippocampal, and anterior hippocampal veins.
The third, posterior or posterior mesencephalic segment, runs medially, superiorly, and
posteriorly from the lateral mesencephalic sulcus, under the pulvinar of the thalamus, to penetrate
the quadrigeminal cistern and generally to drain into the vein of Galen. The main tributaries of the
third or posterior mesencephalic segment are the lateral mesencephalic vein, posterior thalamic,
posterior longitudinal hippocampal, medial temporal, and medial occipital veins (Figs. 60 and 61).
Sometimes, the precentral cerebellar, superior vermian, internal occipital, splenial, medial atrial,
and direct lateral and lateral atrial subependymal veins may drain into the third segment of the
basal vein.
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FIGURE 61. Basal view. The parahippocampal gyrus has been removed. 1, anterior segment of the
uncus; 2, apex of the uncus; 3, inferior surface of the posterior segment of the uncus; 4, anterior
peduncular segment of the basal vein; 5, crus cerebri; 6, anterior longitudinal hippocampal vein,
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dentate gyrus, and fimbria; 7, posterior peduncular segment of the basal vein; 8, lateral
mesencephalic vein and sulcus; 9, medial geniculate body and posterior mesencephalic segment of
the basal vein; 10, pulvinar of the thalamus; 11, internal occipital vein; 12, internal cerebral vein;
13, basal vein; 14, vein of Galen; *, posterior longitudinal hippocampal vein.
The ventricular group is represented by the veins located in the temporal horn that ultimately
drain into the second or peduncular segment of the basal vein of Rosenthal, usually via the inferior
ventricular vein. These include the amygdalar vein, transverse hippocampal veins, inferior choroidal
vein, and inferior ventricular vein.
The amygdalar vein runs medially across the anterior wall on or near the ventricular surface of
the amygdala and ends in the inferior ventricular, basal, or anterior longitudinal hippocampal veins
near the inferior choroidal point, either before or after it has passed through the choroidal fissure to
enter the crural cistern. The transverse hippocampal veins are a group of very fine veins that run
medially across the hippocampus and the collateral eminence. They are divided into an anterior
group, which crosses the floor of the temporal horn, and a posterior group, which crosses the floor
of the atrium. They penetrate the attachment of the fimbria to the hippocampus to enter the
ambient cistern through the fimbriodentate sulcus to drain into the anterior and posterior
hippocampal veins. The inferior choroidal vein runs anteriorly in the temporal horn along the
inferior end of the choroid plexus and ends by joining the inferior ventricular and amygdalar vein or
by passing through the choroidal fissure near the inferior choroidal point to reach the basal vein or
its tributaries. The inferior ventricular vein arises in the posterolateral part of the roof of the
temporal horn and runs anteromedially to exit the temporal horn just behind the inferior choroidal
point to join the basal vein at the most lateral point of the course of the basal vein around the crus
cerebri near the lateral geniculate body (Figs. 46 and 59).
As described by Huang in his extraordinary publication (21), in the angiographic anteroposterior
view, the overall shape of both basal veins resembles the legs of a frog lying on its back with its
toes directed anterolaterally (Figs. 62 and 63). The foot corresponds to the striate segment and is
related superiorly to the anterior perforated substance, laterally to the anterior segment of the
uncus, medially to the optic tract, and inferiorly to the contents of the carotid cistern (Figs. 60, 62,
and 63).
The ankle corresponds posteriorly to the anterior aspect of the crus cerebri, laterally to the
vertex of the uncus (Figs. 62 and 63), and superiorly to the optic tract (Figs. 59 and 60); the leg
corresponds to the anterior peduncular segment and is related superiorly to the optic tract, laterally
to the upper portion of the posteromedial surface of the uncus, and medially to the upper portion of
the crus cerebri (Figs. 62 and 63). The knee corresponds to the most lateral aspect of the crus cerebri
and to the posterior edge of the posterior segment of the uncus, and to the site where the inferior
ventricular vein joins the basal vein (Figs. 62 and 63). It is related laterally to the inferior choroidal
point, superiorly to the optic tract just before this reaches the lateral geniculate body (Fig. 46), and
inferiorly to the contents of the ambient cistern. The uncus therefore is located ahead of the knee
of the basal vein on the angiographic anteroposterior view. The thigh, which includes the posterior
peduncular and the posterior mesencephalic segments, is related medially to the tegmentum of the
midbrain, laterally to the parahippocampal gyrus, superiorly to the medial aspect of the pulvinar of
the thalamus, which is the roof of the wing of the ambient cistern, and inferiorly to the contents of
the wing of the ambient cistern (Figs. 59, 62, and 63).
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FIGURE 62. Anteroposterior view of the basal vein in magnetic resonance angiogram. In this view,
the overall shape of both basal veins resembles the legs of a frog lying on its back with its toes
directed anterolaterally. 1, foot; 2, ankle; 3, leg; 4, knee; 5, thigh.
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FIGURE 63. The anatomic correlation of Figure 62. The “foot” corresponds to the striate segment;
the “ankle” corresponds posteriorly to the anterior aspect of the crus cerebri, laterally to the apex
of the uncus, and superiorly to the optic tract; the “leg” corresponds to the anterior peduncular
segment and is related superiorly to the optic tract, laterally to the upper portion of the
posteromedial surface of the uncus, and medially to the upper portion of the crus cerebri; the
“knee” corresponds to the most lateral aspect of the crus cerebri, to the posterior edge of the
posterior segment of the uncus, and to the site where the inferior ventricular vein joins the basal
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vein. It is related laterally to the inferior choroidal point, superiorly to the optic tract just before this
reaches the lateral geniculate body, and inferiorly to the contents of the ambient cistern. The uncus
therefore is located ahead of the knee of the basal vein on the angiographic anteroposterior view.
The “thigh,” which includes the posterior peduncular and posterior mesencephalic segments, is
related medially to the tegmentum of the midbrain, laterally to the parahippocampal gyrus,
superiorly to the medial aspect of the pulvinar of the thalamus, which is the roof of the wing of the
ambient cistern, and inferiorly to the contents of the wing of the ambient cistern. 1, foot; 2, ankle;
3, leg; 4, knee; 5, thigh.
It is important to emphasize that the pulvinar, which means “pillow” of the thalamus, is the
posterior part of the thalamus and has two free surfaces: an inferior surface, which is the roof of
the wing of the ambient cistern, and a posterior surface, which is divided into two halves; the
lateral half is the anterior wall of the atrium of the lateral ventricle, and the medial half is the roof
of the quadrigeminal cistern.
The lateral angiographic view of the basal vein and its anatomic correlation are demonstrated in
Figures 64 to 66.
Several variations in the draining pattern of the basal vein of Rosenthal have been
described by Wolf et al. (69); one of them, in which the basal vein drains to the lateral
mesencephalic vein and then to the superior petrosal sinus, can be seen in Figures 42, 45, 64, and
65. The overall location of the mesial temporal structures in relation to the rest of the brain can be
seen in Figures 67 and 68.
FIGURE 64. Lateral view. A midsagittal section has been performed with removal of the left
hemisphere. In this case, the basal vein drains to the superior petrosal sinus through the lateral
mesencephalic vein, and consequently there is no posterior mesencephalic segment. 1, corpus
callosum; 2, head of the caudate nucleus; 3, fornix; 4, internal cerebral vein; 5, vein of Galen; 6,
straight sinus; 7, middle cerebral artery (cut); 8, mamillary body and the posterior perforated
substance; 9, striate segment of the basal vein; 10, tentorial edge and the oculomotor nerve; 11,
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peduncular segment of the basal vein; 12, trochlear nerve; 13, superior petrosal sinus.
FIGURE 65. Magnified view of Figure 64. 1, internal cerebral vein; 2, foramen of Monro; 3, splenium
of the corpus callosum; 4, anterior commissure; 5, vein of Galen; 6, straight sinus; 7, posterior
perforated substance; 8, optic nerve and the internal carotid artery; 9, oculomotor nerve and
striate segment of the basal vein; 10, tentorial edge and branches of the superior cerebellar artery;
11, trochlear nerve and lateral mesencephalic vein; 12, tentorial surface of the cerebellum.
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FIGURE 66. Angiographic correlation of Figures 64 and 65. Note that the location of the thalamus on
the lateral angiographic view is approximately depicted by the foramen of Monro anteriorly, the
internal cerebral vein superiorly, and the basal vein inferiorly. 1, venous angle (angle formed by the
thalamostriate and internal cerebral veins that usually denotes the location of the foramen of
Monro); 2, internal cerebral vein; 3, inferior sagittal sinus; 4, vein of Galen; 5, striate segment of
the basal vein; 6, peduncular segment of the basal vein; 7, posterior mesencephalic segment of the
basal vein; 8, straight sinus.
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FIGURE 67. Superior view. The location of the mesial temporal lobe in relation to other structures
of the brain is displayed. 1, frontal lobe; 2, olfactory tract; 3, right orbit; 4, pars orbitalis (inferior
frontal gyrus); 5, genu of the corpus callosum; 6, head of the caudate nucleus; 7, optic nerve and
internal carotid artery; 8, rhinal sulcus; 9, uncus; 10, superior temporal gyrus; 11, insula; 12,
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thalamus; 13, floor of the third ventricle; 14, crus cerebri and oculomotor nerve; 15, posterior
cerebral artery; 16, hippocampus; 17, Heschl’s gyrus (anterior transverse temporal gyrus); 18,
planum temporale (middle and posterior transverse temporal gyri); 19, splenium of the corpus
callosum.
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FIGURE 68
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FIGURE 68. Anteroposterior view. The brain has been sliced coronally at the optic chiasm, and both
thalami along with the basal ganglia have been removed through the choroidal fissure to display
the overall location of the mesial temporal structures in relation to the rest of the brain. 1,
cingulate gyrus; 2, occipital horn; 3, corpus callosum and septum pellucidum; 4, collateral trigone;
5, fornix; 6, parahippocampal gyrus and tentorium; 7, aqueduct and posterior commissure; 8,
dentate gyrus; 9, middle transverse temporal gyrus; 10, Heschl’s gyrus (anterior transverse
temporal gyrus); 11, superior temporal gyrus and sulcus; 12, collateral eminence; 13, amygdala;
14, middle temporal gyrus; 15, inferior temporal gyrus; 16, fusiform gyrus; 17, collateral sulcus;
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18, parahippocampal gyrus; 19, optic nerve; 20, internal carotid artery; *, head of the
hippocampus.
DISCUSSION
One of the major concerns in preparing an anatomic paper aimed toward neurosurgeons is the
usefulness of the offered information in our daily practice; sometimes, the information that is
considered important for anatomists may not be entirely significant for microneurosurgeons, and on
the other hand, there are some critical anatomic landmarks or details that are essential for
neurosurgeons that might be irrelevant for anatomists. Moreover, the practical application of the
anatomic information to a three-dimensional situation, the actual surgery, is sometimes laborious.
For the best demonstration and surgical application of all the anatomic information displayed so far,
a stepwise dissection of the right mesial temporal lobe region as applied to the standard subpial
anterior temporal lobectomy along with amygdalohippocampectomy will be shown, as well as the
location of the mesial temporal structures in a transsylvian approach.
There are still controversies about the parts of the temporal lobe that should be removed in the
treatment of mesial temporal lobe epilepsy as well as disagreement about the best surgical
technique to achieve such a goal (10, 12, 15, 16, 20, 23, 24, 40, 45, 53, 56). Despite current evidence
that better seizure control is directly related to the amount of mesial temporal lobe structures
removed during surgery, this discussion is beyond the scope of this article. In this review, we will
not be focusing on the role played by the mesial temporal structures, but instead, on their location
in actual surgery and on the anatomic landmarks that will guide us when the removal of these
mesial temporal structures is necessary.
Neocortical removal
The standard subpial anterior temporal lobectomy can be divided into three stages: 1)
neocortical removal, 2) hippocampectomy, and 3) amygdalectomy. After exposing the temporal
lobe (Fig. 69), a cortical resection is performed either sparing or including the superior temporal
gyrus. The direction to be followed by the surgeon toward the temporal horn is not as easy as
indicated by diagrams displayed in most of the publications that deal with technical aspects of
temporal lobectomy, in which a coronal section of the temporal lobe is displayed and then the
direction of the dissection is shown. The difficulty of performing a “blind” resection through the
white matter of the temporal lobe is evident, especially for a novice explorer of this region. A useful
landmark to be followed during this stage of the surgery is the tentorial edge; it is useful to
preoperatively assess the relationship of the site of the temporal corticectomy and the tentorial
edge on the coronal view of the magnetic resonance image. As long as the surgeon aims his
neocortical temporal resection lateral to the free edge of the tentorium, there will not be any risk of
entering the sylvian fissure or the inferior circular sulcus of insula or violating any diencephalic or
mesencephalic structure; frequently, at this stage, the temporal horn is entered through its roof.
Once the temporal horn has been entered, the hippocampus and the collateral eminence are
identified; the neocortical removal can be limited medially by the eminence collateral, which
indirectly indicates the superolateral limit of the collateral sulcus on the basal surface of the
temporal lobe (Figs. 70 - 72).
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FIGURE 69. Right temporal lobe exposure for standard anatomic temporal lobectomy and
amygdalohippocampectomy. 1, inferior temporal gyrus; 2, middle temporal gyrus; 3, superior
temporal gyrus; 4, sylvian fissure.
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FIGURE 70. Neocortical removal. The removal of the neocortex is performed either sparing or
including the superior temporal gyrus. The neocortical removal can be “guided” at its depth by
following the tentorial edge; as long as the surgeon maintains the neocortical temporal resection
laterally to the tentorial edge, there will be no risk of entering the sylvian fissure or injuring any
diencephalic or mesencephalic structure. The anteroposterior extent of the neocortical removal
varies from author to author; in general, it ranges from 4.5 to 5.0 cm on the nondominant
hemisphere and 3.5 to 4.0 cm on the dominant hemisphere.
FIGURE 71. Surgical view of the right temporal lobe after the neocortical removal. Frequently,
during the neocortical removal, the temporal horn is entered; in this picture, the choroid plexus has
been retracted medially (under the spatula), and the body of the hippocampus has been retracted
laterally by a dissector. Note that, at the inferior choroidal point, the axis of the hippocampus
changes from anteroposterior (body of the hippocampus) to lateromedial (head of the
hippocampus) from the inferior choroidal point. 1, dura mater of the middle fossa; 2, arcuate
eminence; 3, collateral eminence; 4, head of the hippocampus; 5, fimbria; 6, inferior choroidal
point; 7, spatula; 8, superficial sylvian vein.
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FIGURE 72. Frequently, during the neocortical removal, the temporal horn is entered; after
entering the temporal horn, the intraventricular structures are identified. The neocortical removal
can be limited medially by the collateral eminence, which indicates the superolateral limit of the
collateral sulcus. 1, external acoustic meatus; 2, cerebellum; 3, sigmoid sinus; 4, transverse sinus;
5, temporal pole; 6, hippocampus; 7, choroid plexus; 8, roof of the temporal horn; *, collateral
eminence.
Hippocampectomy
The en bloc hippocampectomy based on anatomic landmarks consists of four steps: 1) opening
of the choroidal fissure, 2) anterior disconnection (“freeing” the head of the hippocampus), 3)
medial disconnection, and 4) posterior disconnection. The lateral disconnection has already been
performed by the time of the neocortical removal.
Inside the temporal horn, the choroid plexus can be identified at the medial side of the
temporal horn. The temporal horn and the choroid plexus are the best anatomic landmarks to be
followed in the temporal lobe: the choroidal fissure can be easily identified by following the choroid
plexus in the temporal lobe, all structures located laterally to the choroidal fissure can be removed,
and all of the structures located medially to it should be preserved. The presence of the choroidal
fissure demarcates the beginning of the body and more posteriorly the tail of the hippocampus, as
the head of the hippocampus is located anteriorly to the inferior choroidal point (Figs. 73 and 74).
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FIGURE 73. After opening the choroidal fissure by splitting the taenia fimbria, the arachnoid
membrane that covers the ambient cistern comes into view (the arachnoid membrane has been
removed). 1, head of the hippocampus; 2, body of the hippocampus; 3, inferior choroidal point and
choroid plexus; 4, basal vein; 5, posterior cerebral artery; 6, choroidal branches (from anterior
choroidal and lateral posterior choroidal arteries); 7, pulvinar of the thalamus; 8, tail of the
hippocampus; 9, roof of the temporal horn.
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FIGURE 74. After opening the choroidal fissure, the en bloc hippocampectomy is performed via
anterior, medial, and posterior disconnections. The anterior disconnection consists of “freeing” the
head of the hippocampus, first anteriorly from the amygdala via subpial removal toward the uncal
recess until visualization of the arachnoid membrane, which covers the oculomotor nerve and the
tentorial edge; then medially by subpial removal of the medial wall of the temporal horn anterior to
the inferior choroidal point until the arachnoid membrane, which covers the P2A segment of the
posterior cerebral artery and the crus cerebri, comes into view. The anterior disconnection proceeds
medially and posteriorly until the choroidal fissure is reached; once the choroidal fissure has been
reached, the third stage of the hippocampectomy, which is the medial disconnection, takes place.
The medial disconnection consists of separating the mesial temporal structures from the contents of
the crural and ambient cisterns through the already opened choroidal fissure. This separation is
based on the identification of the arachnoid membrane, which covers the contents of the ambient
cistern, and on the disconnection of the hippocampal arteries. The route for medial disconnection
will be demonstrated in Figure 75. The posterior disconnection consists of disconnecting the posterior
portion of the fornix, the tail of the hippocampus, and the parahippocampal gyrus laterally to the
choroidal fissure toward the floor of the middle fossa. The dotted line displays the lines of
disconnection. a and b, anterior disconnection; c, posterior disconnection. The medial disconnection
is performed via the choroidal fissure and will be displayed in Figure 75. 1, middle fossa dura mater;
2, body of the hippocampus; 3, head of the hippocampus; 4, fimbria; 5, tail of the hippocampus; 6,
inferior choroidal point.
FIGURE 75. Diagram showing the route for medial disconnection in en bloc hippocampectomy. This
route consists of opening the choroidal fissure via the taenia fimbria, which is the ependyma that
attaches the choroid plexus to the fimbria; once inside the crural cistern, the basal vein (Basal v.)
and the anterior choroidal artery (AchA) are kept intact on the thalamic side, and the disconnection
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proceeds toward the ambient cistern; the hippocampal arteries, which run from the posterior
cerebral artery (PCA) to the fimbrodentate sulcus or hippocampal sulcus, are sacrificed. The inferior
temporal arteries, which arise from the posterior cerebral artery and run on the surface of the
parahippocampal gyrus, can be either preserved or sacrificed, depending on whether the removal
of the parahippocampal gyrus is performed subpially or not. The arrows indicate the route for
medial disconnection. 1, fimbria; 2, hippocampus; 3, brainstem; 4, parahippocampal gyrus; 5,
fusiform gyrus. D, dentate gyrus.
The choroidal fissure can be opened by splitting the taenia fimbriae, a layer of ependymal
covering that attaches the choroid plexus to the fimbria, leaving the choroid plexus attached to the
thalamus (37, 67). At the anterior portion of the opened choroidal fissure, the arachnoidal
membrane, which covers the ambient cistern, comes into view, and the posterior cerebral artery
and its branches and sometimes the basal vein can be identified (Figs. 72 and 73). At the posterior
portion of the choroidal fissure on the temporal horn, the structure that comes to view inferiorly to
the body of the hippocampus after the opening of the choroidal fissure is the parahippocampal
gyrus, as it “closes” medially around and behind the midbrain. At this stage, a prominence on the
thalamic side of the choroidal fissure that marks the beginning of the pulvinar of the thalamus can
be readily identified (Fig. 73).
Once the choroidal fissure has been opened and identified, the next step is the anterior
disconnection. The anterior disconnection consists of “freeing” the head of the hippocampus by
disconnecting it from the uncal recess anteriorly and inferiorly and from the medial wall of the
temporal horn; it is worthwhile to remember that the medial wall of the temporal horn anterior to
the inferior choroidal point is the head of the hippocampus itself.
The uncal recess and the head of the hippocampus are followed medially up to the medial wall
of the temporal horn anterior to the inferior choroidal point. The uncal recess and the head of the
hippocampus will lead us toward the apex and the posterior segment of the uncus, respectively.
The removal of the medial wall of the anterior aspect of the temporal horn by following the uncal
recess and the head of the hippocampus will expose the arachnoid membrane medial to the apex
and the posteromedial surface of the uncus; consequently, the oculomotor nerve and the P2A
segment of the posterior cerebral artery encircling the crus cerebri will come to view underneath
the arachnoid membrane. It is important to emphasize that the visualization of the oculomotor
nerve and the posterior cerebral artery means that the inferior portions of the apex and the
posteromedial surface of the uncus have been removed, but not the superior portions of them; as
stated above, in the great majority of cases, the P2A segment of the posterior cerebral artery is
related to the inferior portion of the posteromedial surface of the uncus; therefore, there is still the
superior portion to be removed.
After “freeing” the anterior portion of the anterior temporal horn, the anterior disconnection is
continued laterally up to the collateral eminence (Fig. 74). The anterior disconnection proceeds
medially and posteriorly until the choroidal fissure is reached; then, the third stage of the
hippocampectomy, medial disconnection, takes place. The medial disconnection consists of
separating the mesial temporal structures from the contents of the crural and the ambient cisterns
through the already opened choroidal fissure. This separation is based on the identification of the
arachnoid membrane that covers the contents of the ambient cistern and on the division of the
hippocampal arteries.
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After the opening of the choroidal fissure through the taenia fimbriae, there is an additional
arachnoid membrane with vessels entering the temporal lobe below the head of the hippocampus
and perpendicular to that of the ambient cistern, usually before reaching the arachnoidal
membrane of the ambient cistern. This is the arachnoid membrane carrying the hippocampal
arteries and veins through the hippocampal notch, and these vessels should be disconnected to
free the head of the hippocampus. This arachnoid membrane separates the inferior surface of the
posterior segment of the uncus superiorly from the parahippocampal gyrus inferiorly.
Now the rest of the hippocampus can be freed through the choroidal fissure and can be
connected to the “free” head of the hippocampus. However, soon after splitting the taenia fimbria
(the lateral posterior choroidal and anterior choroidal arteries and the inferior ventricular vein are
kept intact on the thalamic side, because the choroid plexus is maintained intact and attached to
the thalamus), the arachnoid membrane of the ambient cistern comes into view; again, there is
another arachnoid membrane that is perpendicular to that of the ambient cistern and is directed
toward the temporal lobe a short distance below the fimbria, and once again, this arachnoid
membrane carries the hippocampal arteries and veins through the hippocampal sulcus. These
vessels should be disconnected to free the body and the tail of the hippocampus. This part of the
hippocampal sulcus, located behind the head of the hippocampus, is another important landmark as
it separates the dentate gyrus superiorly from the parahippocampal gyrus inferiorly (Fig. 75).
The final disconnection at the hippocampal stage is the posterior one that is directed from the
choroidal fissure laterally toward the floor of the middle fossa or toward the tentorium, depending
on the extent of the hippocampus to be removed. If the whole hippocampus should be removed,
the landmark that denotes the end of the tail of the hippocampus is where the tail of the
hippocampus meets the calcar avis, the inferior prominence on the medial wall of the atrium of the
lateral ventricle (Figs. 73 and 74).
After the removal of the lateral and medial temporal cortex along with the mesial temporal
structures that include the hippocampus, fornix, and parahippocampal gyrus, the neural and
vascular elements of the ambient cistern come into view, namely, the crus cerebri, tegmentum of
the midbrain, posterior cerebral artery, and basal vein of Rosenthal; sometimes, the trochlear
nerve and the superior cerebellar artery can also be seen (Fig. 76).
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FIGURE 76. After the removal of the lateral and basal temporal cortex along with the mesial
temporal structures (hippocampus, fimbria, parahippocampal gyrus, but not amygdala), the neural
and vascular elements of the ambient cistern (covered by arachnoid membrane) come into view. 1,
anterior disconnection; 2, crus cerebri; 3, posterior cerebral artery; 4, basal vein; 5, choroid plexus
and roof of the temporal horn; 6, pulvinar of the thalamus; 7, parahippocampal gyrus; 8, atrium.
Amygdalectomy
The whole temporal or principal amygdala is located within the boundaries of the uncus; in the
subpial anterior temporal lobectomy, in which the uncus is approached subpially from its lateral
aspect, the arteries constitute the most important anatomic landmarks for this purpose.
The anteromedial surface of the uncus is related to the internal carotid artery and the proximal
half of the M1 segment of the middle cerebral artery; the inferior portion of the vertex of the uncus
is related to the oculomotor nerve; the inferior and the superior portions of the posteromedial
surface of the uncus are related, respectively, to the P2A segment of the posterior cerebral artery
turning around the crus cerebri and to the posterior part of the cisternal segment of the anterior
choroidal artery just before entering the temporal horn through the choroidal fissure. Superiorly,
there is no clear demarcation between the amygdala and the globus pallidus.
The subpial resection of the uncus can be based on the vascular landmarks visualized through
the arachnoid membrane: anteriorly, the visualization of the internal carotid artery and the
proximal segment of the middle cerebral artery indicates that the anteromedial surface of the uncus
has been removed; the visualization of the oculomotor nerve denotes that the inferior portion of
the vertex of the uncus has been removed; the removal of the inferior portion of the posteromedial
surface of the uncus displays the P2A segment of the posterior cerebral artery; the main question
that remains is the superior limit of the removal, since there is no limit between the amygdala and
the globus pallidus.
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If we examine the medial surface of the uncus carefully, the best anatomic landmark as the
superior limit for the removal of the uncus is the optic tract; however, during the subpial resection
of the uncus, the optic tract is usually not visualized. The next landmark that could be followed is
the cisternal segment of the anterior choroidal artery, as it runs under the optic tract; however, as
shown in Figure 53, the initial portion of the cisternal segment of the anterior choroidal artery does
not always follow the superior portion of the uncus, whereas its posterior portion, close to the
inferior choroidal point, is constantly related to the superior portion of the posteromedial surface of
the uncus. When viewed from its medial aspect, the highest point of the uncus is located at the end
of its posteromedial surface, namely at the level of the inferior choroidal point. So the inferior
choroidal point is actually the posterosuperior limit observable of the uncus, and it is easily
identified intraoperatively. Anteriorly, the highest point of the uncus that is discernible
intraoperatively is at the carotid bifurcation and/or the proximal segment of M1.
If a line is traced from the bifurcation of the internal carotid artery or the proximal segment of
M1 to the inferior choroidal point (carotid-choroidal line), almost the entire uncus will stay below
this line. Intraventricularly, the posterior portion of the amygdala is the prominence on the roof of
the temporal horn immediately anterior to the inferior choroidal point, which passes below this line,
and it can be removed until this line is established. It is not advisable to cross this line superiorly
because of the risk of invading the globus pallidus; it is not advisable to remove the cerebral tissue
located deeply in the angle formed by the internal carotid artery bifurcation because of the risk of
invading the anterior perforated substance as well. This so-called carotid-choroidal line has been
used by the author in temporal lobectomies (mesial temporal sclerosis) for the last 3 years, and it
has proven to be a reliable landmark for amygdalectomy (Fig. 77).
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FIGURE 77. Magnetic resonance image. Postoperative coronal views of an anatomic standard
subpial temporal lobectomy. The removal of the right amygdala was performed following the
carotid-choroidal line. Note that a small layer of the amygdala was left. The removal of the
hippocampus was performed following the choroidal fissure.
Finally, after the complete removal of the temporal lobe, including the amygdala and the
hippocampus, the surgeon must be able to visualize the following structures through the arachnoid
membrane: the internal carotid, middle cerebral, posterior communicating, anterior choroidal, and
posterior cerebral arteries, the oculomotor nerve, the basal vein, the crus cerebri, the lateral
mesencephalic sulcus and vein, the tegmentum of the mesencephalon, and sometimes the fourth
nerve and the superior cerebellar artery (Figs. 78 - 83).
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FIGURE 78. After the complete subpial removal of the temporal lobe including the
amygdalohippocampectomy, the contents of the crural and ambient cisterns (covered by arachnoid
membrane) come into view. 1, optic nerve; 2, internal carotid artery; 3, oculomotor nerve; 4,
tentorial edge; 5, temporal pole; 6, crus cerebri; 7, basal vein and anterior choroidal artery; 8,
remaining amygdala; 9, vein draining the roof of the temporal horn, tributary of the inferior
ventricular vein; 10, pulvinar of the thalamus; 11, parahippocampal gyrus; 12, atrium.
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FIGURE 79. Continuation of Figure 78. Overall view of the contents of the crural and ambient cisterns
(after removal of the arachnoid membrane). 1, optic nerve; 2, internal carotid artery; 3,
oculomotor nerve; 4, posterior clinoid process; 5, pons; 6, trochlear nerve; 7, posterior cerebral
artery; 8, crus cerebri; 9, temporal pole; 10, remaining amygdala; 11, pulvinar of the thalamus.
FIGURE 80. Magnified view of Figure 79. 1, oculomotor nerve entering the posterior portion of the
roof of the cavernous sinus; 2, superior cerebellar artery; 3, posterior communicating artery; 4,
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P2A segment of the posterior cerebral artery; 5, origin of the anterior choroidal artery; 6, basilar
artery and P1 segment of the posterior cerebral artery; 7, crus cerebri; 8, lateral mesencephalic
vein; 9, cisternal segment of the anterior choroidal artery and basal vein; 10, tegmentum of the
mesencephalon; 11, remaining amygdala; 12, inferior choroidal point; 13, inferior ventricular vein;
14, roof of the temporal horn.
FIGURE 81. Surgical view of the contents of the crural and the ambient cisterns after the right
temporal lobectomy and the amygdalohippocampectomy. 1, internal carotid artery; 2, oculomotor
nerve; 3, posterior communicating artery; 4, pons; 5, P2A segment of the posterior cerebral
artery; 6, lateral mesencephalic vein; 7, anterior choroidal artery; 8, crus cerebri; 9, tegmentum of
the mesencephalon; 10, inferior choroidal point; 11, choroid plexus of the temporal horn.
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FIGURE 82. Continuation of Figure 80. The posterior cerebral artery and its branches have been
removed to display the vascular and neural structures underneath. 1, pons; 2, pontomesencephalic
sulcus and vein; 3, lateral mesencephalic vein; 4, tegmentum of the mesencephalon; 5, crus
cerebri; 6, anterior choroidal artery (cisternal segment); 7, anterior peduncular segment of the
basal vein; 8, posterior peduncular segment of the basal vein; 9, posterior mesencephalic segment
of the basal vein; 10, inferior ventricular vein and plexal segment of the anterior choroidal artery;
11, pulvinar of the thalamus; 12, tail of the hippocampus; *, vein of Galen.
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FIGURE 83. Continuation of Figure 82. All of the vascular structures have been removed to display
the neural structures underneath. 1, basilar artery (cut); 2, internal carotid artery (cut); 3,
interpeduncular sulcus (between the superior and middle cerebellar peduncles); 4, superior
cerebellar peduncle; 5, oculomotor nerves; 6, crus cerebri; 7, lateral mesencephalic sulcus; 8,
inferior colliculus; 9, tuber cinereum; 10, mamillary bodies; 11, superior colliculus; 12, pineal
gland; 13, optic tract; 14, lateral geniculate body; 15, medial geniculate body; 16, splenium of the
corpus callosum; 17, pulvinar of the thalamus; 18, choroid plexus.
The amygdalohippocampectomy can also be performed via the transsylvian route (75), although
it is essential that the microneurosurgeon know the exact location of the mesial temporal structures
from the transsylvian perspective and the anatomic landmarks that will allow us to approach them
safely. For the transsylvian approach to mesial temporal structures, the head of the patient is
positioned in a way that the sylvian fissure is parallel to the surgeon’s view. After completely
splitting the sylvian fissure as posteriorly as possible, the inferior circular sulcus of the insula is
entered inferiorly through the temporal stem and the roof of the temporal horn, at the level of or
just posterior to the limen insulae, until the temporal horn is reached (63, 76).
It is worth mentioning that through the inferior circular sulcus of insula, the entry point through
the roof of the temporal horn is located on average 8 mm from the lateral aspect of the lateral
geniculate body; therefore, we are less than 1 cm away from the thalamus when this approach is
performed, and one should keep in mind that there is no demarcation between the lateral
geniculate body of the thalamus and the roof of the temporal horn, since the major component of
the roof of the temporal horn is constituted by the optic radiation or geniculocalcarine fascicle,
which originates from the lateral geniculate body. Consequently, a more medial removal of the roof
of the temporal horn during this approach to improve visualization of the choroidal fissure should
be performed with caution.
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performed. At the stage of uncal removal through the transsylvian approach, the same landmarks
as described earlier for the subpial temporal lobectomy can be adopted.
The lateral limit of amygdalar removal is the rhinal sulcus; anteriorly, the anteromedial surface
of the uncus is removed anterior to the M1, after sacrificing the branches from the internal carotid
artery, middle cerebral artery, and anterior choroidal artery to the uncus; the medial and superior
removal of the uncus can be performed following the optic tract, since this is clearly visible from
inside the cistern; posteromedially, the removal of the inferior portion of the posteromedial surface
of the uncus is completed when the P2A segment of the posterior cerebral artery comes into view;
the posterior limit of uncal resection is the inferior choroidal point when the choroid plexus of the
temporal horn comes to view (Figs. 84 - 88). These landmarks have been used by the authors to
selectively resect lesions in and around the uncal area (Figs. 89 and 90).
FIGURE 84. Transsylvian exposure. 1, right orbit; 2, olfactory tract; 3, optic nerve and internal
carotid artery; 4, oculomotor nerve; 5, planum polare; 6, rhinal sulcus; 7, anteromedial surface of
the uncus; 8, M1 segment of the middle cerebral artery; 9, limen insulae; 10, superior temporal
gyrus.
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FIGURE 85. Transsylvian exposure. A coronal cut has been performed at the temporal pole
demonstrating that there is no amygdala located at that level. 1, anterior clinoid process; 2,
posterior clinoid process; 3, oculomotor nerve and tentorial edge; 4, rhinal sulcus (beneath the
temporal branches of the middle cerebral artery); 5, anteromedial surface and apex of the uncus;
6, M1 segment of the middle cerebral artery.
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FIGURE 86. Continuation of Figure 85. Another coronal cut was performed on the temporal lobe at
the level of the middle cerebral artery. Note that the collateral sulcus is located laterally to the
tentorial edge, and the amygdala bulges inferiorly toward the head of the hippocampus. 1, middle
meningeal artery; 2, V2 and V3 (trigeminal nerve); 3, temporal horn; 4, collateral sulcus; 5,
occipito-temporal sulcus; 6, collateral eminence; 7, apex of the uncus; 8, amygdala; 9, inferior
temporal sulcus; 10, middle temporal gyrus; 11, limen insulae.
FIGURE 87. Continuation of Figure 86. An additional coronal cut has been made at the level of the
limen insulae. Note that, at this level, the cavity of the temporal horn is projected at the level of
the tentorial edge. 1, lamina terminalis; 2, internal carotid and posterior communicating artery; 3,
head of the hippocampus; 4, collateral sulcus and collateral eminence; 5, fusiform gyrus; 6,
amygdala; 7, limen insulae; 8, short gyri of the insula.
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FIGURE 88. Anatomic frontal view of the specimen shown in Figure 87. 1, inferior temporal gyrus; 2,
collateral eminence; 3, parahippocampal gyrus; 4, oculomotor nerve; 5, right optic nerve; 6,
amygdala; 7, apex of the uncus; 8, internal carotid artery; 9, lamina terminalis; 10, superior
temporal gyrus; 11, limen insulae.
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FIGURE 89. Surgical view of the removal of the amygdala and the anterior portion of the
parahippocampal gyrus via the right transsylvian route, following the optic tract and anterior
choroidal artery as the superior limit, the M1 segment of the middle cerebral artery and the internal
carotid artery as the medial limit, the cavity of the temporal horn and the inferior choroidal point as
the posterior limit, and the tentorium edge and the rhinal sulcus as the inferolateral limit. 1, optic
nerve; 2, internal carotid artery; 3, oculomotor nerve; 4, pons; 5, P2A segment of the posterior
cerebral artery; 6, genu of the middle cerebral artery; 7, crus cerebri.
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FIGURE 90. Magnetic resonance image. Postoperative coronal view displaying the removal of the
amygdala via the transsylvian approach; the anatomic correlation can be seen in Figure 88.
CONCLUSION
With the advances accomplished in the fields of basic neuroscience and neuroimaging, the
mechanisms, the circuitry of the pathogenesis, and the images of the lesions involving the temporal
lobe are becoming better understood and better visualized; with knowledge of the
three-dimensional microsurgical anatomy, these lesions can be better approached and more
precisely resected. It is our concept that the anatomy of the brain should be known from different
angles, not only from the angle that is usually shown in the classic textbooks of anatomy, since the
anatomy is the same. We should observe the brain’s anatomy from multiple views; the observation
of the same anatomy from several different angles will assemble an authentic tridimensional
knowledge. It is our firm belief that the neurosurgeon’s mind, laden with knowledge of
three-dimensional microsurgical anatomy, is the best microsurgical navigational system for the
great majority of microsurgical procedures in the brain.
ACKNOWLEDGMENTS
We thank Ronald Smith, M.S., Director of the Microneuroanatomy Laboratory, Department of
Neurological Surgery, University of Florida, and Toshiro Katsuta, M.D., Department of
Neurosurgery, Kyushu University, for constant support. We also extend special appreciation to
Cecília Emi Tsukamoto for help in preparing the manuscript.
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COMMENTS
Wen et al. present the microsurgical anatomy of the temporal lobe in an elegant and meticulous
fashion. The detailed description of the anatomic relationships of the temporal mediobasal region
(temporal pole, amygdala, hippocampus, parahippocampus), in addition to the description of
amygdalohippocampectomy, presented in the article should serve as a guide in resecting limbic and
paralimbic tumors (4).
The authors’ comprehensive review and description of the topographic anatomy and associated
vascular structures of the temporal lobe provide the neurosurgeon with a detailed and precise map
of this region during microsurgical procedures. The authors have presented a superb article with
excellent illustrations. This article will most likely become a valuable benchmark reference for
temporal lobe microsurgical anatomy.
Variations in the origin and course of blood vessels in the mediobasal temporal lobe region are
not infrequent. The understanding of the topographic relationship and variations in the origin and
course of the posterior communicating, anterior choroidal, and middle cerebral arteries and their
respective branches and perforators, as well as the perforators of the internal carotid artery, which
may arise separately, is of crucial importance to the microvascular surgeon (3). Variability in the
respective venous systems are more common. The article elegantly describes the course of the
basal vein of Rosenthal. The basal vein can have variation throughout its course, including
connections to the sphenoparietal sinus anteriorly and direct drainage into the straight sinus, the
superior petrosal sinus, or a tentorial sinus (1, 2). As the authors have at their disposal such a
unique collection of injected brain blood vessels, it would be immensely appreciated if, in future
publications, they were to study the vascular variability in this region, using their excellent
methodology.
M. Gazi Yasargil
Saleem I. Abdulrauf
Little Rock, Arkansas
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[Context Link]
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2134–2139. [Context Link]
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Aneurysms. Stuttgart, Georg Thieme Verlag, 1984, vol I, p 66. [Context Link]
4. Yasargil MG: Microneurosurgery: Microneurosurgery of CNS Tumors. Stuttgart, George Thieme Verlag,
1996, vol IV-B, p 252. [Context Link]
In a presentation based on the dissection of 52 brains, the authors manage to beautifully show
details of temporal lobe anatomy, using cuts and dissections that have not been used in classic
anatomy textbooks and frequently mimicking surgical approaches. The brain dissections are
extremely esthetic, didactically clear, and very accurate.
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The article is divided into three sections: anatomic aspects, vascular relationships, and surgical
approaches. Obviously, several parts of this presentation have previously been described, such as
the general anatomic aspects of the temporal lobe. Others, centered on the
amygdalohippocampectomy technique and the vascular relationships, are of great interest to
neurosurgeons in the field of epilepsy surgery.
We found the description of the surgical steps for amygdalohippocampectomy very useful. The
term “selective amygdalohippocampectomy,” although widely used as surgical term, is anatomically
incorrect: it is not selective, nor is all of the amygdala removed, nor is only the hippocampus
removed. Quite contrarily, Siegel et al. (1) showed that this procedure works best when the
parahippocampal gyrus is included in the removal. Usually, if one looks at postoperative magnetic
resonance images, the gyrus lateral to the parahippocampal gyrus up to the collateral sulcus is
included in the resection, as shown in Figure 90 of the article and frequently seen in our own cases
and in other publications. Concerning the amygdala, the mesial nuclei of the amygdaloid body are
usually left behind; these mesial nuclei reach mesial of the M1 segment of the middle cerebral
artery into the temporal stem. The procedure that we perform is really a subtotal amygdalectomy,
total uncectomy, partial hippo- and parahippocampectomy plus transection of the temporal stem.
Nevertheless, the term is used universally, but one should be aware of what it really means.
One aspect that we find most difficult during dissection of the hippocampal body is the
arachnoid covering of the vessels that enter from the ambient cistern into the hippocampal sulcus.
In our internal jargon, we like to call it “vascular pedicle” or “mesentery of the hippocampus.”
These vessels are usually branches from the choroidal artery or the posterior cerebral artery and
should be cut deep within the hippocampal sulcus for a very specific reason. Sometimes, a loop of
the choroidal artery proper or a major branch of the posterior cerebral artery loops directly into the
hippocampal sulcus and could thus be injured if the vessels of the “hippocampal mesentery” are cut
too close to the arachnoid membrane that separates the hippocampus from the ambient cistern.
Especially if the hippocampus is to be removed en bloc, the dissection of the vessels of the
hippocampal fissure, as shown in Figures 14, 42, 73, and 81 of the article, is much more difficult
than when the hippocampus is removed by suction. The authors have presented beautiful
dissections showing these vascular relationships.
One minor point may be raised: is the normally found location of the most mesial aspect of the
uncus medial to the temporal edge really a herniation? In general clinical terminology, a herniation
represents a pathological movement of an anatomic structure.
This exquisitely illustrated article represents extremely good value for the readers of
Neurosurgery, as it is equivalent to a book chapter. It contains most detailed and esthetic anatomic
dissections that are very useful for the interested epilepsy surgeon but would also be very useful
for the oncological neurosurgeon, when confronted with a temporomesial tumor and the necessity
to expose the lateral aspect of the brainstem, with its major arteries and the optic tract near by.
However, there are tumors that push the mesial border of the temporal lobe far beyond the
tentorial edge, destroying the normal anatomic landmarks, such as the hippocampal body,
obliterating the choroidal fissure, and making dissection very difficult. Knowing the content of this
article will help both the oncological surgeon and the epilepsy neurosurgeon.
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Johannes Schramm
Ingmar Bümcke Neuroanatomist
Bonn, Germany
1. Siegel AM, Wieser HG, Wichmann W, Yasargil GM: Relationships between MR-imaged total amount of
tissue removed, resection scores of specific mediobasal limbic subcompartments and clinical outcome
following selective amygdalohippocampectomy. Epilepsy Res 6: 56–65, 1990. SFX-UHN Bibliographic
Links [Context Link]
Amygdala; Anterior choroidal artery; Basal vein; Choroidal fissure; Microsurgical anatomy;
Temporal lobe epilepsy; Uncus
Accession Number: 00006123-199909000-00028
Copyright (c) 2000-2006 Ovid Technologies, Inc.
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