Intraoperative subdural hematoma in a patient with arachnoid cyst in the middle cranial fossa.

A case of arachnoid cyst in the middle cranial fossa complicated by intraoperative subdural hemorrhage is presented. Accumulation of cerebrospinal fluid (CSF) outside the outer wall of the arachnoid cyst was found to induce the rupture of well-developed, fragile leptomeningeal vessels at the base of the middle cranial fossa. This phenomenon is noteworthy as a pitfall in surgery for intracranial arachnoid cyst and suggests the bleeding source of subdural hematoma occasionally associated with this lesion.