Cavum velum interpositum

A cavum velum interpositum (CVI) is a normal variation where there is a dilated CSF space involving the velum interpositum, which extends below the splenium of the corpus callosum and columns of the forinces and above the internal cerebral veins. It is triangular in shape, the apex pointing anteriorly reaching as far forward as the foramina of Monro ^1,4-5. 

When larger than 1cm in axial transverse measurement, with outwardly bowed margins and positive mass effect,  the term cyst of the velum interpositum or cavum velum interpositum cyst should be used. 

Epidemiology

A cavum velum interpositum is a relatively frequent finding on imaging of infants and young children seen in 18-34% of infants younger the 2 years of age ¹. In most cases this space closes as the individual ages. 

Clinical presentation

This variation is often detected incidentally and individuals are usually asymptomatic. Sometimes this space is not only visible but expanded as a cystic space in which case patients may have symptoms relating to altered CSF flow (obstructive hydrocephalus leading to headache). 

Unlike the cavum septum pellucidum and cavum vergae, a cavum velum interpositum has not been associated with neurophyschiatric disorders ¹. 

Radiographic features

Neonatal ultrasound

May be seen as a cystic space in pineal region, and is more common in this age group than either pineal cysts of arachnoid cysts ¹. The internal cerebral veins (best seen on colour doppler) can be seen below the cystic space ¹.  

CT / MRI

Classically seen as an enlarged CSF space situated behind the foramen of Monro, beneath the columns of the fornices and above the tela choroidea of the 3^rd ventricle. On axial images may have a triangular configuration pointing anteriorly, its anterior extent never extending further than the foramen on Monro ⁵.

On coronal imaging the fornices are elevated and splayed ⁵. 

Treatment and prognosis

In the vast majority of cases patients are asymptomatic. In cases where cystic dilatation is present with positive mass effect and obstruction to normal CSF flow, then surgical (endoscopic) fenestration may be curative ¹. 

Differential diagnosis

• cavum septum pellucidum
  • located anterior to the foramen of Monro, between the frontal horns
  • also triangular but with the apex pointing posteriorly
• cavum vergae
  • rectangular in cross-section (parallel wall)
  • located superior to the columns of the fornices, which are displaced inferiorly
• pineal cyst
  • ovoid or spherical
  • located below the internal cerebral veins
  • abutting the colliculi
• arachnoid cyst of the quadrigeminal cistern 
  • usually eccentric, and not triangular in cross section
  • located below the cerebral veins
  • abutting the colliculi

Related articles