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  • Updated 03.22.2024
  • Released 06.16.1995
  • Expires For CME 03.22.2027

Cavum septi pellucidi and cavum Vergae



The septum pellucidum is a non-neural dual membrane structure originating from the medial parts of the embryonic cerebral hemispheres. Right and left leaves of the septum are, therefore, part of the embryonic origin of the cerebral hemispheres. The opposing leaves are separated by a cavity in fetal life, which gradually becomes thinner and obliterates. Its posterior extension is the cavum Vergae. The roof is formed by the corpus callosum and the hippocampal commissure, and the posterior and inferior of the septum is bordered by the fornices. The midline cavities of the brain are often involved in malformations that affect the midline structures of the brain, such as callosal agenesis. Delay of the normal closure of the cavum septum pellucidum may be a first warning sign in routine ultrasound studies of the fetal brain. In this way, abnormalities of the cavities, mostly by size, may indicate the need for further examinations. The size of the cavum septum pellucidum after birth varies considerably. Normal variability versus a possible relationship to acquired brain disorders has caused a stream of studies, also discussed in this article.

Key points

• The cavum of the septum pellucidum is bordered by two leaflets that closely approximate during the first year of life.

• The cavum Vergae is a posterior extension of the former.

• The leaves of the cavum contain no vital structures.

• Pathologies of the cavum, as detected by MRI, include its persistence, as well as complete absence of the septal leaflets resulting in a single cavity. Both anomalies may form part of complex congenital disorders.

• Pathology of the cavum is not harmful in itself but may draw attention to pathology in adjacent neural structures.

• Increased width of the cavum is nonspecific but may reflect spatial compensation for lack of brain growth in the fetus or brain atrophy in adults.

Historical note and terminology

The septum pellucidum is a double vertical membrane that separates the corpus callosum from the columns of the fornix and intervenes between the lateral ventricles. The septum has right and left leaves, each of which is part of the respective medial hemispheric border. The anatomist Sylvius of Leyden University first described cavum septi pellucidi in 1671 (07). Cavum Vergae is a posterior extension of the cavum septi pellucidi, communicating with the cavum septi pellucidi but lying posterior to the columns of the fornix (70). In the early literature, these cavities were considered to be the fifth and sixth cerebral ventricles, respectively. They are not actually ventricles because they are not primarily part of the ventricular system, are not lined by cells of the ependyma, and do not contain choroid plexus. The anatomic boundaries of the cavum septi are the medial hemisphere walls on the lateral sides; the roof is formed by the corpus callosum. The cavum septi pellucidi is bordered posteriorly by the column of the fornix. The cavum Vergae is bordered anteriorly by the posterior border of the cavum septi pellucidi, inferiorly by the body of the fornix, and superiorly and posteriorly by the corpus callosum. Anatomically, the two cavities are not separated. Another cavity, known as the cavum veli interpositi, is part of the leptomeningeal space and intervenes between the roof of the third ventricle and the body of the fornices. When the corpus callosum is absent, the cavum septi becomes unroofed and, therefore open to the leptomeningeal space.

Cavum septi pellucid and cavum Vergae
In this drawing of the midline cavities, notice that the cavum septi pellucid and cavum Vergae are continuous structures. (Contributed by Dr. Peter Barth.)

The formation of the cavities was detailed by Rakic and Yakovlev, who analyzed the brains of 113 fetuses and numerous vertebrate species. The human samples covered the crucial period of 13 to 14 weeks during which commissuration takes place (52). According to this study, the cavum septi is a part of the leptomeningeal space sealed off by the developing corpus callosum. The septum pellucidum is made of two opposed sheaths of tissue derived from the medial walls of the hemispheres. Its lower edge is bordered by the columns of the fornix (53). The inferior and posterior border of the septum pellucidum is formed by the columns of the fornix, which are part of the limbic system, connecting to the hippocampi. Because of their close anatomic relationship, absence of the septum leads to ectopia of the fornices and absence of the forniceal commissure. The lateral, ventricular surface of the septum pellucidum is covered with ependyma; the medial surfaces (when not fused) are poorly organized and appear glial in neonates. The cores of the pellucidal leaves contain small myelinated fibers (53). Dandy first described cysts of the cavities in 1931 (10).

The midline cavities are essentially temporary embryonic structures that involute during late pregnancy and infancy. Persistence of these structures beyond this period does not cause any symptoms but is statistically related to malformations and psychiatric disturbances, mainly dependent on size (Table 1).

The size of persistent midline cavities is differently measured because size may be measured by antero-posterior extent or by width. The former approach is generally used in MR studies of neuropsychiatric populations, eg, with schizophrenia (47). The latter approach is usual in younger groups where persistence of the structure itself is rated less significant than increased transverse size. It should be stressed that progressive decrease in width of the cavities during pregnancy and infancy parallels transverse growth of the cerebral hemispheres, and, in this regard, decrease of the cavities may be seen as compensatory to the increase of brain size. A significant correlation has been found between biparietal diameter and size of the cavum septi pellucidi (26).

Table 1. Midline Cavities in Normal Persons

Measurement by US or MRI in controls



36 to 40 weeks fetal age


<9,5 mm
<8,0 mm


Newborn 39 to 40 weeks of age

Average width

6.3 mm +/- 0.83 (1 sd)


Children and adults

Maximal length
Maximal length
Maximal length

< 6 mm
< 6 mm (> in 3- 8.7%)
<5.6 mm (> in 11.5%)


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