Arachnoid cyst with traumatic intracystic hemorrhage unassociated with subdural hematoma.

Arachnoid cysts of the middle cranial fossa may manifest themselves in several different ways. Most often they remain asymptomatic and are only diagnosed incidentally on computed tomography or at autopsy. When they are symptomatic, headache, nausea, vomiting and seizures are most common in the patients with increased intracranial pressure. Increased intracranial pressure is caused by the ball-valve mechanism of the cyst's membrane which is in communication with the general subarachnoid space or arachnoid cells which contain specialized membranes and enzymes which have secretory activity. A significant number of middle cranial fossa arachnoid cysts are associated with subdural hematoma which may, in turn, be associated with intracystic hemorrhage. We report an unusual case with posttraumatic, isolated intracystic hemorrhage of the arachnoid cyst in the sylvian area without subdural hematoma.