Cavum septi pellucidi and cavum vergae

Peter G Barth MD PhD (Dr. Barth of the University of Amsterdam has no relevant financial relationships to disclose.)
Gary D Clark MD, editor. (Dr. Clark has no relevant financial relationships to disclose.)
Originally released June 16, 1995; last updated March 9, 2017; expires March 9, 2020

This article includes discussion of cavum septi pellucidi and cavum vergae, cavum septum pellucidum, and cava septi pellucidi et vergae, and it includes information on their embryology and associated pathologies. The foregoing terms may include synonyms, similar disorders, variations in usage, and abbreviations.

Overview

The septum pellucidum is a non-neural dual membrane structure originating from the medial parts of the cerebral hemispheres. Right and left leaves of the septum are separated by a cavity in fetal life, which gradually becomes thinner and obliterated. Its posterior extension is the cavum vergae. The roof is formed by the corpus callosum and the hippocampal commissure, and posterior and inferior of the septum is formed by the fornix. The midline cavities of the brain are involved in inherited and congenital disorders. Although moderate variations in size are asymptomatic, they are easily picked up by neuroradiological means such as ultrasonography during fetal life. In this way, abnormalities of the cavities may indicate the need for further examinations. The author presents the complex association with pathology in this clinical summary. His past and present work is in the realm of congenital and inherited disorders affecting the morphology of the central nervous system.

Key points

 

• The cavum of the septum pellucidum is bordered by 2 leaves that fuse 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, and they normally fuse before 6 months of age.

 

• 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 cava is not harmful in itself but may draw attention to associated pathology in 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 thin vertical membrane that connects the corpus callosum to the columns of the fornix and separates the lateral ventricles. The septum has right and left leaves, each of which is part of the respective medial hemispheric border. Sylvius first described cavum septi pellucidi in 1671 (Bruyn 1977). 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 (Verga 1851). 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 pellucid, inferiorly by the body of the fornix, and superiorly and posteriorly by the corpus callosum. Anatomically, the 2 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.

Image: Cavum septi pellucid and cavum vergae
When the corpus callosum is absent, the cavum septi becomes unroofed and, therefore, unidentifiable.

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 (Rakic and Yakovlev 1968). 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 2 apposed sheaths of tissue derived from the medial walls of the hemispheres. Its lower edge is bordered by the columns of the fornix (Raybaud 2010). 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 (Raybaud 2010). Dandy first described cysts of the cavities in 1931 (Dandy 1931).

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 (Nopoulos et al 1997). 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 (Jou et al 1998).

Table 1. Midline Cavities In Normal Persons

 

Measurement by US or MRI in controls

Size

References

36 to 40 weeks fetal age

Width
Length

<9,5 mm
<8,0 mm

(Mott et al 1992)

Newborn 39 to 40 weeks of age

Average width

6.3 mm +/- 0.83 (1 sd)

(Jou et al 1998)

Children and adults

Maximal length
Maximal length
Maximal length

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

(Nopoulos et al 1998)
(Born et al 2004)
(Takahashi et al 2008)

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