Cavum veli interpositi

A cavum veli interpositi (CVI) is a normal variation where there is a dilated CSF space involving the velum interpositum. When larger than 1 cm in axial transverse measurement, with outwardly bowed margins and positive mass effect, the term cyst of the velum interpositum or cavum veli interpositi cyst should be used. 

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 veli interpositi has not been associated with neurophyschiatric disorders 1

The cavum veli interpositi extends below the splenium of the corpus callosum and the column of the fornix 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

A cavum veli interpositi is a relatively frequent finding on imaging of infants and young children seen in ~25% (range 18-34%) of infants younger than 2 years of age 1. In most cases this space closes as the individual ages. 

Neonatal ultrasound

May be seen as a cystic space in pineal region, and is more common in this age group than either pineal cysts or 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 3rd ventricle

On axial images may have a triangular configuration pointing anteriorly, its anterior extent never extending further than the foramen of Monro 5.

On coronal imaging the fornices are elevated and splayed 5

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

  • 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

Pineal region masses

The pineal region is anatomically complex and plays host to a number of unique masses and tumours as well as potentially affected by many entities seen more frequently elsewhere in the brain. 

General reading

Pathology 

Neuroanatomy
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Article Information

rID: 10708
Section: Anatomy
Synonyms or Alternate Spellings:
  • Cavum velum interpositi
  • Cavum velum interpositum (CVI)
  • Cavum veli interpositi
  • Cavum velum interpositum cyst
  • Cyst of the velum interpositum
  • Cavum velum interpositum

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    Figure 1: lateral view
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    Figure 2: anterior view
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    Case 1
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    Case 4: large
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    Case 6: cavum veli interpositi (annotated CT)
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