Cavum velum interpositum

Findings

There is a fluid density structure between the bodies of the lateral ventricles. The septum pellucidum is intact. This structure splays the fornices laterally.

Differential Diagnosis:
- Cavum velum interpositum (CVI)
- Cavum septum pellucidum (CSP)
- Cavum vergae (CV)
- Arachnoid cyst
- Epidermoid cyst


Diagnosis: Cavum velum interpositum


Key points

CVI is a cystic dilation of the cistern of the velum interpositum (usually a potential space)
M=F, prevalence decreases with age.
Not associated with other anomalies if found prenatally.
Usually incidentally detected. Rarely, large ones may cause obstructive hydrocephalus.
On axial images, it is a triangular shaped CSF collection between the bodies of the lateral ventricles that is below the fornices. It contains the internal cerebral veins.
Does not extend anterior to the foramina of Monro. (Distinguishes from CSP and CV).
On MR, no contrast enhancement, follows CSF on all sequences, suppresses on FLAIR and no diffusion restriction (distinguishes from epidermoid cyst).
May be indistinguishable from arachnoid cyst.
Usually no treatment needed unless symptomatic. In these cases, may be fenestrated or shunted.