cavum veli interpositi cavum veli interpositi in the brain, the cavum veli interpositi (cvi) is a condition in which the cistern of the velum interpositum becomes dilated. the phenomenon usually occurs in newborns. cavum veli interpositidifference between cavum septi pellucidi (csp), cavum vergae (cv), and cavum veli interpositi (cvi). 3=third ventricle, 4=fourth ventricle.anatomical terms of neuroanatomy axial mr/ct show a triangular-shaped cerebrospinal fluid (csf) space between the lateral ventricles. on sagittal images, cvi can appear as a slit-like, linear-to-round/ovoid csf collection below the fornices, and above the 3rd ventricle. there are usually no associated abnormalities, although larger lesions may cause an obstructive hydrocephalus. no treatment is usually necessary.