SONOGRAPHIC CHARACTERISTICS OF THE CAVUM VELUM INTERPOSITUM

BACKGROUND AND PURPOSE: Differential considerations for pineal region CSF collections include both true cysts and normal cystlike anatomic v ariations. Our purpose was to determine the sonographic characteristic s of pineal region fluid spaces that reflect the presence of a normal persistent cavum velum interpositum (CVI). METHODS: Eighteen neonates and infants who had sonographic findings of ''cysts'' in the pineal re gion were examined prospectively with conventional sonography and colo r Doppler sonography to evaluate the shape of the fluid collection and its anatomic relationship with the color-coded internal cerebral vein s. Subsequent MR images were obtained in eight of these infants to det ermine the exact nature of the cystlike collections. RESULTS: The cyst like spaces in the pineal region were of an inverted helmet shape in 1 4 subjects and roundish in four. All were situated inferior or slightl y anteroinferior to the splenium of the corpus callosum and 2.5 to 4 m m away from the quadrigeminal plate. The internal cerebral veins were either inferior (n = 12) or inferolateral (n = 6) to the cystlike spac es at sonography. Subsequent MR studies confirmed eight of these cystl ike spaces to be the posterior portion of the CVI. CONCLUSION: The CVI may appear as a cyst in the pineal region on neonatal sonograms, Usua lly, it has a characteristic inverted helmet shape and is situated ben eath the fornices and above the internal cerebral veins.