Epidermoid cysts of the velum interpositum.

The cistern of the velum interpositum is a space located between the corpus callosum dorsally and the roof of the third ventricle ventrally. Lesions located within the velum interpositum are rare and include meningiomas, pilocytic astrocytomas, atypical teratoid/rhabdoid tumors and arachnoid cysts. Epidermoid cysts in this location have not been reported previously. We report the clinical and radiological features of two patients with epidermoid cysts located in the velum interpositum. The patients presented with gait difficulty and features of raised intracranial pressure and magnetic resonance imaging demonstrated large tumors in the velum interpositum with intensities suggestive of epidermoid cysts. There was ventral displacement of the internal cerebral veins and dorsal displacement of the corpus callosum in keeping with a mass in the velum interpositum. Tumors of the third ventricle displace the internal cerebral veins dorsally. A transcallosal approach was used in both patients to effectively excise the tumors.