[Vermian epidermal cyst developing in the fourth ventricle. A case report].

A 34-year-old man presented with recent severe headache. Neurological examination found gait disturbance and a static cerebellar syndrome. The CT scan showed a tumor located in the fourth ventricle and which presented with a density close to that of the cerebellar parenchyma, without contrast enhancement, associated with an enlargement of the third and the lateral ventricles. MRI showed that the tumor had an heterogeneous hyposignal on T1-weighted images and an hypersignal on T2-weighted images, without associated edema; the roof of the fourth ventricle was displaced upward and the brain stem forward. At operation, an encapsulated epidermal cyst, developed from the cerebellar vermis, without attachment to the floor of the fourth ventricle, was totally removed. Epidermal cysts of the fourth ventricle are unusual lesions; their capsule often adhere to the floor and cannot be totally removed. Those developed from the cerebellar vermis seem to be rarer. With the use of MRI, their true origin could be suspected. In these cases, the cysts can be totally removed, reducing the risk of recurrence