Subarachnoid hemorrhage in an adolescent with spontaneous occlusion of the left middle cerebral artery and reconstruction by collateral vessels (Moyamoya phenomenon).

A case of a 12-year-old girl with subarachnoid hemorrhage and a hematoma in the pineal region is reported. With cerebral angiography, an occlusion of the left middle cerebral artery and its reconstruction by numerous dilated lenticulostriate collateral vessels were demonstrated. Subarachnoid hemorrhage in children with Moyamoya phenomenon is a rare event that may result from rupture of dilated collateral vessels or associated microaneurysms.