Download Anatomical variations of septum pellucidum

Update in Radiology
Anatomical variations of septum pellucidum
P. Sartori*, V. Anaya, Y. Montenegro, M. Cayo and G. Barba
Computed Tomography and Magnetic Resonance Imaging Department, EDES, Hospital Español, Ciudad Autónoma de Buenos Aires, Argentina
Abstract Septum Pellucidum is a thin medial septum of triangular shape that consists of two nervous laminae that are
attached and located between the corpus callosum and the fornix.
Anatomical variations of septum pellucidum appear during fetal life in the ventro-dorsal position. These variations are:
cavum septi pellucidi, cavum vergae and cavum veli interpositi.
The presence or absence of these cavities can be related to the presence of nervous system or
neuropsychiatric dysfunction, therefore they should be well known to avoid wrong diagnoses
© 2014 Sociedad Argentina de Radiología. Published by Elsevier Spain, S.L.U. This is an open access article under the
CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
Keywords: Septum pellucidum; Cavum septum pellucidum; Cavum vergae; Cavum vellum interpositum
Introduction
During intrauterine life, there are normal midline cavities
which usually persist in adulthood and should not be confused with pathological entities. It is important to know
them, as they may may be related to concomitant neurological or neuropsychological diseases. In this article, we review
the septum pellucidum (SP) and its anatomical variations.
In Latin, the word septum (saepire) means fence or partition
wall, while pellucidum or perlucidum means translucent. Thus,
SP (or lucidum) is a thin medial septum of triangular shape that
consists of two nervous laminae that are attached and located
between the corpus callosum and the fornix (fig. 1)1-5. In 1966,
Andy and Stephen called it “telencephalic septum” (septum
telencephali) 6. Boundaries are described in table 11,4-6.
The SP serves as a relay station, containing fibers that connect with hippocampus and the hypothalamus2. Complete
absence of the SP occurs in 2 to 3 individuals per 100 000
people, being a predictor of brain abnormalities, such as:
septooptic dysplasia, corpus callosum abnormalities, holoprosencephaly, lissencephaly or Chiari malformation6,7.
During intrauterine life, there are three potential cavities in
the midline between the lateral ventricles. These cavities regress between the seventh month of fetal life and the second
year of postnatal life, but some may persist in adulthood8,9.
These cavities, first described in the year 1600, include: cavum
septum pellucidum (CSP), cavum vergae (CV) and cavum veli
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interpositi (CVI). They occur with a prevalence of 0.14%8-10.
It is important to highlight that these cavities are in direct contact with the subarachnoid space, but they do not communicate with or are considered part of the ventricular system. As
these cavities are not lined with ependyma or choroid plexus
cells, they do not produce cerebrospinal fluid (CSF)3,9-11.
1) Cavum septum pellucidum: it is also known as cavum septi
pellucidi, the ventricle of the septum or fifth ventricle (fig.
2)3,8,10,12. It can be found in all fetuses at 36 weeks’ gestation and persists in 36% of full-term infants, only 6% of
them persist after the six month of live3,4,11-13. It is significantly more common in women3.
CSP is part of normal development. As from 12 weeks of
gestational age, the corpus callosum starts to develop from
the lamina terminalis as a fiber bundle that connects the two
hemispheres, also originating the SP. The space between the
two laminae that are not fused, located between the frontal
horns of the lateral ventricles and anterior to the foramen of
Monro is called CSP (fig. 3)10,11,14.
A number of theories have been proposed for the origin of
CSP, but it is thought that during embryo-fetal development,
the mass of cells occupying the space of the SP is involved in
the development of the commissural plate. Selective elimination of this group of cells would lead (by necrosis) to the
molecular concentration of large amounts of amino acids,
which would attract fluids to achieve a balance in the oncotic
pressure of the plate. Fluid pressure would be responsible for
P. Sartori et al.
the formation of CSP12. However, it has also been hypothesized that this entity may originate during infancy, as a result
of repeated shaking, when rocking infants vigorously in an
attempt to soothe them12.
CSP is a triangular space between the two laminae of the
septum pellucidum (its boundaries are detailed in table
2)3,4,8,10,12,13,15,16. CSP may occur in isolation or in association with cavum vergae, communicating with the latter
through the aqueductus caudae septi or aqueductus ventriculii vergae7,8.
CSP is an important marker for the evaluation of normal development of the fetal neural axis. Absence of the CSP is rarely an isolated finding, as nonvisualization of the CSP on ultrasound (US) or magnetic resonance imaging (MRI) scans in
fetal life is associated with brain malformations, such as holoprosencephaly, septo-optic dysplasia, agenesis of the corpus
callosum, Alexander disease, tuberous sclerosis, phakomatosis, pinealoma, trisomy 21 and schizencephaly3,10,12,14,16.
Considering embryonic development, CSP may not occur
without the development of the corpus callosum; therefore
agenesis of the corpus callosum is always associated with
agenesis of the SP3,4.
There are US studies in which CSP has been identified in
100% of fetuses between 18 and 37 weeks’ gestation, and
in 79% of fetuses between 30 and 41 weeks’ gestation; in
newborns, complete posterior closure has been seen in 97%,
so the CSP is present when the cavum vergae is absent16.
Hence, visualization of the CSP between 18 and 20 weeks’
gestation implies normal development of the brain16.
In patients with schizophrenia or in aggressive, alcoholic individuals or people with neurological development disorders,
there is a higher prevalence of enlarged CSP3-5,11,14,15,17,18.
It was De Greef who first reported an association between
CSP and schizophrenia11.
Some authors report an association between boxing and the
presence of CSP due to repeated brain trauma. An association between CSP and posttraumatic stress disorders has also
been reported, in the military population currently participating in war conflicts or in veterans of wars2,3,5,12,13,15,17.
There are various classifications for CSP. Based on whether
the CSP communicates with the lateral ventricles through
fenestrations, it may be classified as communicating or noncommunicating (more common)2,13. However, another classification focuses on asymptomatic (communicating or non-
Table 1: Boundaries of the septum pellucidum.
BoundaryStructure
SUPERIOR
Inferior surface of the body
of corpus callosum
ANTEROINFERIOR Superior surface of the genu
of corpus callosum
POSTEROINFERIOR Corpus and columns of the fornix
Figure 1 Axial T2-weighted magnetic resonance imaging of
the brain demonstrating normal appearance of the septum
pellucidum (lucidum) (arrow).
LATERAL
Medial wall of frontal horns of lateral ventricles
MEDIAL
Virtual space with contralateral septum
Figure 2 Sketch of axial and sagittal views of the cavum septum pellucidum.
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Anatomical variations of septum pellucidum
communicating CSP) and symptomatic (non-communicating
CSP) characteristics; the latter may be simple, not complicated or complicated by brain injuries12.
2) Cavum vergae: Andrea Verga, an italian anatomist described it in 1851. Iit is also known as cavum fornicis, cavum
psalterii, Verga´s ventricle, the ventricle of Strambio, ventriculus triangularis or sixth ventricle10,12,13. Cavum vergae is
the posterior extension of CSP, extending as far as the posterior columns of the fornix and the foramen of Monro (fig.
4)9,10,13. It is triangular in shape (its boundaries are listed in
table 3)4,5,10,13.
Cavum vergae begins to develop by the 5th month of gestation and disappears by two months of age 10. CV is present
in 30% of normal newborns, subsequently regressing and
disappearing13.
The incidence of CV was 2.3% in 1032 brains studied, and it
is important to highlight that it is almost always found in association with CSP7,9,10,13 When the CSP is dilated, the CV is
also dilated, as they join through a defect of the fornix, which
is not in contact with the corpus callosum10 (fig. 5).
Some authors report a higher prevalence of enlarged CSP or
CV in patients with schizophrenia10.
3) Cavum velum interpositum (CVI) was first described by
Kruse and Schaetz in 19309,10. It is also known as cisterna
interventricularis, ventriculi tertii, transverse fissure or subtrigonal fissure9. The incidence of CVI ranges, according to
various authors, between 21 and 34%, and persistence in
postnatal life is rare, being 30% in 1-10 year-old children,
with no significant differences between genders9.
CVI is a subarachnoid cistern arising as an extension of the
cisterna magna and which originates from the roof plate of
the diencephalo, protruding into the primitive neural tube
approximately during the third fetal month. CVI is a normal
Table 2: Boundaries of the cavum septum pellucidum.
BoundaryStructure
ANTERIOR
Genu of corpus callosum
POSTERIOR
Corpus and columns of the fornix
SUPERIOR
Inferior border of the body of
corpus callosum
INFERIOR
Rostrum of the corpus callosum
and anterior white commissure
LATERAL
Laminae of septum pellucidum
Table 3: Boundaries of the cavum vergae..
BoundaryStructure
ANTERIOR
Crus of the fornix
POSTERIOR
Body of the corpus callosum
SUPERIOR
Splenium of the corpus callosum
INFERIOR
Hippocampal commissure and
psalterium (lyra davidis)
Figure 3 Axial T1-weighted magnetic resonance of the brain
demonstrating the presence of a triangular cavity between
the frontal horns of the lateral ventricles, known as cavum
septum pellucidum (arrowhead).
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Figure 4 Sketch of axial and sagittal views of the cavum septum pellucidum associated with the cavum vergae.
P. Sartori et al.
Figure 5 Axial T2-weighted magnetic resonance of the brain
demonstrating a cavity filled with cerebrospinal fluid and interposed between the lateral ventricles (asterisk). The finding
is consistent with cavum septum pellucidum associated with
cavum vergae.
Figure 7 FLAIR axial magnetic resonance imaging of the brain
showing a triangular cavity cephalic to the fornix, between the
lateral ventricles, called cavum velum interpositum (arrowhead).
Table 4: Boundaries of the cavum velum interpositum.
BoundaryStructure
SUPERIOR
Figure 6 Sketch of axial and sagittal view of the cavum velum
interpositum.
cavity in the development of the brain9,10 (fig. 6) and its presence has not been associated with neuropsychiatric disorders
or dysfunction of the limbic system19.
CVI is a triangular cavity of dorsal base located in the choroidal fissure (fig. 7). The boundaries of CVI are detailed in
table4 4,9,10,13,19,20.
It is important do distinguish CVI from CV. One of the main
features is the fact that CV always coexists with CSP, but
these entities can also be differentiated by the location of the
internal cerebral veins, as CV lies above these veins, whereas
CVI encloses them.
Corpus callosum (lower border)
and hipoccampal commissure
INFERIOR
Tela choroidea of the third ventricle
and thalamus
LATERAL
Crus of the fornix
ANTERIOR
Foramen of Monro
POSTERIOR
Pineal region
INFEROLATERAL Internal cerebral veins
CVI should also be differentiated from an arachnoid cyst of
the quadrigeminal cistern or from a pineal cyst. The latter lies
inferiorly to the internal cerebral arteries9,19.
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Conclusion
It is important to recognize anatomical variations of the septum pellucidum so that they may not be wrongly diagnosed as
interhemispheric cystic lesions, whether before or after birth.
Recognition of such variations during fetal life serves as a
predictor for the detection of brain malformations or behavior disorders.
Conflicts of interest
The authors declare no conflicts of interest.
Figure 8 Coronal fetal ultrasound showing the cavum septum
pellucidum (asterisk).
Imaging diagnosis of SP and variants
Prenatal diagnosis is made by transabdominal ultrasound
and, in the case of cephalic presentation, transvaginal ultrasound allows better visualization of its variants (fig. 8)10.
The columns of the fornix should be differentiated from a
CSP to avoid making mistakes, and the same applies to enlarged CSP in the presence of CV, when the latter laterally
displaces the CSP leaflets mimicking an absent CSP14,17.
Differential diagnosis for an enlarged CSP include vein of Galen aneurysm (which is diagnosed by color Doppler technology with knowledge of the anatomy of the region), arachnoid
cyst and dilated third ventricle (distinguished by its location
between the thalami)14.
In the fetus, CSP and CV can be seen by US and MRI, although the latter may replace US in cases of maternal obesity
and olighohydramnios3,5,14,21. MRI has the advantage of delineating the pineal gland with respect to the quadrigeminal
cistern or pineal cysts, differentiating such cysts from CVI21.
The anterior extension of the CVI is best displayed on axial
T2-weighted MR images, while the posterior extension of the
CVI can be seen as an anechoic inverted helmet-like structure on US scans (the convex side of this helmet is formed
by the internal cerebral veins). Differential diagnosis is made
on the basis of the position of the internal cerebral veins,
as arachnoid cysts compress the tectum towards the brain
and displace the internal cerebral veins upward against the
splenium of the corpus callosum (which differentiates them
from the CVI)21.
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