The cavum vergae (CV), along with the cavum septum pellucidum (CSP) is a persistence of the embryological fluid-filled space between the leaflets of the septum pellucidum and is a common anatomical variant. The CV is sometimes referred to as the 6th ventricle.

The CV is the posterior extension of the CSP, posterior to the anterior columns of the fornix, lying inferior to the splenium of the corpus callosum, but it may exist independently.

anteriorly: fornix

posteriorly: splenium of the corpus callosum

superiorly: body of the corpus callosum

inferiorly: transverse fornix

The CV and CSP usually close in 6th week in utero but may persist in 30% of term infants and 15% of adults 3. During development, these spaces obliterate postero-anteriorly: the CV followed by the CSP. Because of this ordered obliteration, a CSP almost always accompanies a CV may not always occur in the same sequence 1-2.

Cavum septum pellucidum

Cavum velum interpositum

Cavum vergae cyst