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KOR J CEREBROVASCULAR DISEASE
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March 2001 Vo. 3, No 1, page 5-10
Microsurgical Anatomy of the Basilar Artery：
：
Surgical Approaches to the Basilar Trunk and
Vertebrobasilar Junction Aneurysms
Department of Neurosurgery, Saga Prefectural Hospital, Saga, Japan
Shuji Sakata, MD
ABSTRACT
The success of treating basilar aneurysms lies in the preservation of all perforating arteries and best selection of the surgical
approaches. The purpose of this study was to define the microsurgical anatomy of the basilar artery and surgical approaches to the basilar
artery. The microsurgical anatomy of the basilar artery and its branches were evaluated in adult cadaveric brains using 3x to 20x
magnification. The branches of the basilar artery can be divided into three main groups：the cerebellar, lateral pontine, and perforating
arteries. The lateral pontine arteries arise from the basilar trunk and course laterally to the brachium pontis. The perforating arteries
originated from the basilar trunk and penetrating near the midline of the pons on its basal surface. The basilar trunk was approached via
subtemporal-transtentorial, anterior transpetrosal, posterior transpetrosal and transchondylar routes. Selection of approach for basilar
aneurysms was discussed. (Kor
( J Cerebrovascular Disease 3:5-10, 2001))
KEY WORDS：Microsurgical anatomy·Basilar artery·Perforating artery·Surgical approach.
Introduction
Surgical management of basilar trunk and vertebrobasilar
junction aneurysms remains a challenge for neurosurgeons.3)7)11) The aneurysm of this area are located deep in the
surgical field and intimately related to the cranial nerves
and the brain stem, and are blocked by petrous bone. The
surgical exposure and obliteration of aneurysms in this
region continues to be associated with high morbidity. Inappropriate approach and technical errors including perforator injury are important factors that influence postoperative high morbidity.1)
It is obligatory to have a precise knowledge of the microsurgical anatomy of the basilar artery and to know via
which route the aneurysm can be best approached in order
to provide better result. Intensive studies of microsurgical
anatomy of the cerebellar branches (SCA, AICA, PICA)
논문접수일：2001년 5월 10일
심사완료일：2001년 9월 5일
교신저자：Shuji
교신저자：Shuji Sakata, Koseikan, 1-12-9 Mizugae, Sagacity, Saga,
Japan Department of Neurosurgery, Saga Prefectural Hospital
Tel：81-952-24-2171・Fax：81-952-29-9390
E-mail：[email protected]
have been published.5)8)10) However, The basilar artery is
rarely the subject of the anatomical examination in recent
literature.9)15)
The purpose of this study was to define the microsurgical anatomy of the basilar artery and surgical approaches to
the basilar artery.
Materials and Methods
The Microsurgical anatomy of basilar artery and its branches were examined using 3x to 20x magnification after
perfusing the vessels with a colored silicone to facilitate
dissection in the ten adult cadaveric heads. The basilar trunk
was approached via subtemporal-transtentorial, anterior transpetrosal, posterior transpetrosal (combined supra/infratentorial transpetrosal), and transchondylar routes.
Results
1. Microsurgical anatomy of the basilar artery (Fig. 1)
) Basilar artery
1)
The two vertebral arteries joined together forming the basilar artery(BA) in the area of the pontomedullary sulcus.
5
Microsurgical Anatomy of the Basilar Artery
The BA coursed upward in the prepontine cistern in a
shallow groove in the mid sagittal line on the ventral surface of the pons, which was called the basilar sulcus. The
BA usually reached the interpeduncular fossa at about the
level of the pontomesencephalic junction where it divided
into two posterior cerebral arteries. The basilar artery was
frequent deviated from the midline, especially in older age
group.
) Branches of the BA
2)
The branches of the basilar artery can be divided into three
main groups：the cerebellar, lateral pontine, and perforating arteries.
(1) Cerebellar arteries
① Superior cerebellar artery (SCA)
The SCA arose near the bifurcation of the basilar artery.
The SCA usually arose as a single trunk, but may also arise
as duplicate arteries. It encircled the midbrain near the pontomesencephalic junction, passing below the oculomotor and
trochlear nerves and above the trigeminal nerve. After passing above the trigeminal nerve, it entered the precerebellar
space. Upon leaving this space, its branches were distributed the superior parts of the cerebellar cortex.
② Anterior inferior cerebellar artery (AICA)
The AICA originated from the initial part of the basilar
artery. The AICA usually arose as a single trunk, but it may
also duplicate arteries or as triplicate arteries. From its origin, the AICA coursed backward around the pons near the
abducent, facial, and vestibulocochlear nerves. After passing near the nerves, entering the acoustic meatus, it proceeded around the flocculus on the middle cerebellar peduncle.
A
③ Posterior inferior cerebellar artery (PICA)
The PICA usually arose from the vertebral artery. If the
PICA was defined as the cerebellar artery that supplied the
posteroinferior part of the cerebellum and that generally
arose from the vertebral artery, it may also arise from the
basilar artery. In some cases, the PICA arose by a common
trunk with the AICA. The PICA had the most complex
relationship to the cranial nerves of any artery. The vertebral artery coursed anterior to the glossopharyngeal, vagus,
accessory nerves and the proximal part of the PICA passed
around or between the rootlets of these and adjacent nerves.
(2) Lateral pontine arteries (circumferential perforating
arteries)
The lateral pontine arteries (circumferential perforating
arteries) arose from the basilar trunk and course laterally to
the brachium pontis. These branches gave off small perforating vessels that penetrated a lateral surface of the pons
and brachium pontis. These branches of the basilar artery
can be divided into the pontomedullary, large lateral arteries, and posterolateral artery.
① Pontomedullary artery
The pontomedullary artery was located close to the pontomedullary sulcus. The artery was usually single, and rarely
duplicated. The artery coursed close to the pontomedullary
sulcus, and terminated in the rostrolateral part of the medulla.
② Large lateral pontine artery
The large lateral pontine arteries ranged in number from
1 to 3 on each side, but most often two vessels were present. They usually originated from the distal half of the basilar arteries. The artery coursed laterally the ventral sur-
B
Fig. 1. A：Anterior view of the whole course of the basilar artery and its branches. Basilar artery (BA), Vertebral artery (VA),
Superior cerebellar artery (SCA), Anterior inferior cerebellar artery (AICA), Posterior inferior cerebellar artery (PICA). B：Enlarged
view showing the large pontine artery (Large P.A.), and paramedian perforating arteries (Perforators).
6
Kor J Cerebrovascular Disease 3:5-10, 2001
Shuji Sakata
face of the pons and terminated on its lateral surface and
brachium pontis. The artery often supplies the lateral pyramidal bundles, the central tegmental tract, the trigeminal
nerve, and the trigeminal nuclei.
③ Posterolateral artery
The posterolateral artery arose from the basilar artery
just caudal to the origin of the superior cearebellar artery. It
coursed laterally, parallel to the SCA, and terminated in the
rostrolateral part of the pons.
A
(3) Perforating arteries(Paramedian perforating arteries)
The perforating arteries originated from the basilar trunk
and penetrating near the midline of the pons on its basal
surface. They can be divided into three groups：the caudal,
middle, rostral groups.
① Caudal perforating arteries
The caudal perforating arteries arose from the most proximal portion of the basilar artery and entered the foramen
caecum. They ranged in number from 1 to 4. The arteries
B
Fig. 2. A：Subtemporal transtentorial approach to the upper part of the basilar trunk. The tentorium was incised from the incisura
to the transverse sinus. The basilar trunk can be seen between the trochlear nerve (Ⅳ) and tringeminal nerve (Ⅴ). B：Superior
view of the petrous bone. The area of resecton for anterior petrosal approach is surrounded by the trigeminal ganglion anteriorly,
the sphenopetrosal groove laterally, the cochlear organ posterioly, and the internal auditory canal and carotid canal inferiorly.
A
B
Fig. 3. A：Combined supra/infra tentorial transpetrosal approach to the middle portion of
the basilar trunk. The posterior
pet-rosectomy exposed the semicircular canals. The temporal
lobe is elevated and the tentorium is transected parallel to
the petrous bone to the tentorial
incisura, exposing the basilar
trunk. B：Enlarged view showing the vertebrobasilar junction
and basilar trunk.
Kor J Cerebrovascular Disease 3:5-10, 2001 7
Microsurgical Anatomy of the Basilar Artery
mainly supply the abducent nucleus, medial longitudinal
fasciculus, and caudomedial pontine reticular formation.
② Middle perforating arteries
The middle perforating arteries originated from the middle part of the basilar artery and usually penetrated the pons
along the edge of the basilar sulcus. The number of the perforators from each BA ranged from 5 to 9. The middle perforating arteries supply the pyramidal bundles, part of the
medial lemniscus, the medial portion of the reticular formation, and the medial longitudinal fasciculus.
③ Rostral perforating arteries
The rostral perforating arteries originated from the terminal portion of the basilar artery and entered the caudal
part of the interpeduncular fossa. The vessels varied in
number from 1 to 5.
2. Surgical approaches to the basilar trunk and vertebrobasilar junction
Three approaches to gain access to the basilar trunk and
Fig. 4. Transchondylar approach to the right vertebrobasilar junction. The vertebrobasilar junction and lower part of the basilar trunk can be seen through the lower cranial nerves. Trigeminal nerve (Ⅴ), Acoustic nerve (Ⅷ), Hypoglossal nerve (Ⅸ).
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Kor J Cerebrovascular Disease 3:5-10, 2001
vertebrobasilar junction were examined.
) Subtemporal transtentorial approach, Anterior tran1)
)(Fig. 2)
spetrosal approach (Kawase’s approach)
(1) Subtemporal transtentorial approach
A traditional middle subtemporal approach was performed and temporal lobe was retracted. The tentorium was
opened as wide as possible；the incision extended close to
the transverse sinus laterally and to the pyramidal edge anteriorly. Direct retraction of the pons and trigeminal nerve
are facilitated to expose basilar trunk. Exposure can be obtained as deep as the junction of the vertebral arteries by
wide opening of the tentorium. Disadvantage of subtemporal approach is the possibility of postoperative edema or
hemorrhage in the temporal lobe.
(2) Anterior transpetrosal approach (Kawase’s approach)
The temporal lobe was elevated by extradural approach.
The middle meningeal artery was sacrificed at the foramen
spinosum, and the petrous segment of the carotid artery was
exposed in Glasscock’s triangle. The area of drilling was
surrounded by the trigeminal ganglion anteriorly, the cochlear organ posterioly, the shenopetrosal groove laterally,
and the carotid canal and internal auditory canal inferiorly.
The dural sleeve of the internal auditory canal can be identified by tracing the greater petrosal nerve posteriorly to the
geniculate ganglion (lateral aspect of internal auditory canal).
The location of the internal auditory canal can be also estimated by bisecting the 120-degree angle between the greater petrosal nerve and the arcuate eminence. The bone of
Kawase’s triangle was resected to the depth of the inferior
petrosal sinus to expose the dura of the posterior fossa. The
temporal lobe dura was opened and a second incision was
made along the floor of the middle fossa toward the posterior fossa dura. The superior petrosal sinus was sectioned
at the level of Kawase’s triangle. The tentorium cerebelli
was then sectioned into the incisura. The basilar trunk was
approached between the fifth and seventh cranial nerves.
) Posterior transpetorosal approach, Combined supra/
2)
infratentorial approach(Fig. 3)
A L-shaped supra/infratentorial craniotomy was performed to complete the bone exposure. A partial mastoidectomy skeletonizing the labyrinth, posterior fossa dura, sigmoid sinus, and superior petrosal sinus was accomplished.
This radical posterior petrosectomy facilitated to gain sufficient exposure of the presigmoid dura from the superior pet-
Shuji Sakata
rosal sinus to the level of the juglar bulb. The temporal dura
was incised parallel to the transverse sinus. The presigmoid
posterior fossa dura in the Trautmann’s triangle inised up
to the superior petrosal sinus with ligation of the superior
petrosal sinus. The temporal lobe was slightly elevated and
the tentorium was transected parallel to the petrous bone to
the tentorial incisura. After the tentorium had been cut completely, the sigmoid sinus and the remaining portion of the
tentorium were retracted, exposing the basilar artery from
the upper basilar region down to the level of the vertebrobasilar junction and ipsilateral vertebral artery.
) Far lateral approach, Transchondylar approach(Fig. 4)
3)
After the muscle and soft tissue were reflected, a retromastoid craniectomy was extended through the foramen
magnum, and the inferior portion of the mastoid process
was drilled away to expose the distal sigmoid sinus and
juglar bulb. The vertebral artery was isolated above the
posterior arch of C-1. The remaining anterolateral rim of
the foramen magnum and the lateral portion of the C-1 were
removed to include the posterior one- third of the occipital
condyle. Removal of the condyle is the key step giving a
more direct approach to the distal intradural vertebral artery
and vertebrobasilar junction without the need for retraction
of the neural structural.
Discussion
Aneurysms of the lower basilar trunk and vertebrobasialr junction are located in sort of “no man’s” land. Numerous approaches have been attempted to gain access to
aneurysms of the basilar trunk and vertebrobasilar junction.1-7)11)12)15) Classical routine approaches are subtemporal
transtentorial and suboccipital approaches.
In 1944, Dandy2) described an approach via the suboccipital route. This exposure has been associated with significant morbidity, especially for aneurysms locating at the
midline. In 1965, a subtemporal-transtentorial approach was
described by Drake.4) Opening the tentorium facilitates visualization of basilar artery trunk aneurysm. Sometimes,
direct retraction of the pons and trigeminal nerve are required to expose aneurysms. Disadvantage of subtemporal
approach, however, is the possibility of postoperative edema
or hemorrhage in the temporal lobe.6)7)12) In this region, the
subtemporal and suboccipital approaches can only applied
with considerable difficulty and risk of damage to the nei-
ghboring neurovascular structures of the brainstem and
cranial nerves.
A number of cranial base approaches such as the anterior
petrosal,1)6) the combined supra/infratentorial posterior transpetrosal,3)11) and extended far lateral approaches3)7) have
been reported. A guiding principle in cranial base techniques has been to create maximum surgical exposure by
removing bone rather than retracting brain.1)3)6)7)11) A direct
approach to the basilar trunk aneurysms often blocked by
the petrous bone and the main component of many of these
cranial base approaches to the basilar artery is the removal
of petrous bone.
Selection of the approach for the basilar trunk aneurysms
Upper clival basilar aneurysms are relatively easily accessible by either the traditional pterional or the subtemporal approach.11) Exposure of the aneurysms in this region
can be enhanced by addition of posterior clinoidectomy,
transcavernous approach, or transtentorial approach.12) Extended orbitozygomatic approach was proposed for large
upper clival aneurysms.3)
Midclival basilar aneurysms are located at the middle of
the clivus anterior to the pons. This area is exposed best by
the anterior1)6) or posterior7)11) transpetrosal approaches. Midclival basilar aneurysms located between the floor of the
sella turcica and the internal auditory canal are successfully
exposed by anterior transpetrosal approach. Midclival basilar aneurysms at or below the internal auditory canal and
above the upper margin of the jugular tubercle can be best
exposed by posterior petrosectomy.1)
Lower clival basilar aneurysms below the jugular tubercle and most aneurysms of the ventral artery can be satisfactory reached by addition of the retrochondylar farlateral,
transchondylar, or suboccipital approach.7)13)14)
Conclusion
The success of treating basilar aneurysms lies in the
preservation of all perforating arteries and best selection of
the surgical approach. The Microsurgical anatomy of basilar artery and its perforating branches were examined.
The upper clival basilar aneurysms can be relatively easily
accessible by either the traditional pterional or the subtemporal approach. Midclival basilar aneurysms ca be exposed
best by the anterior or posterior transpetrosal approaches.
Lower clival basilar aneurysms can be satisfactory reached
Kor J Cerebrovascular Disease 3:5-10, 2001 9
Microsurgical Anatomy of the Basilar Artery
transchondylar approach.
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