[Unusual extra-axial infra-tentorial localization of a cavernoma in the cisterna magna]

A case of an extra-axial cavernous angioma of the cisterna magna is described. The clinical presentation, radiographic features, treatment of that unusual location in the posterior fossa are discussed. The patient is a 31 years old man admitted for the sudden onset of occipital headache and instability. A CT scan demonstrated a slightly calcified lesion, minimally enhanced after intravenous injection of a contrast agent, located within the posterior fossa. A T2-weighted MR image showed a well circumscribed mass, located between medulla oblongata and left cerebellar tonsil, of mixed signal intensity surrounded by a rim of decreased signal intensity related to the presence of hemosiderin. Cerebral arteriography was normal. A medial suboccipital craniectomy was performed, with the patient in the ventral position, in which a 1.5 x 1 cm solid dark-red mass was encountered arising from the cisterna magna and was easily removed "en bloc". The operative extra-axial aspect of that lesion was evident excluding a medulla oblongata tumor protruding into the cisterna magna. Histologically, the lesion was a cavernous angioma consisting of numerous vascular channels with collagen fibrous walls filled with fibrin thrombi and hemosiderin. Few elastic fibers were found in vascular walls. The patient's post-operative course was unremarkable.