Middle cranial fossa arachnoid cyst presenting with subdural effusion and endoscopic detection of tear of the cyst--case report.

A 15-year-old boy presented with a case of middle cranial fossa arachnoid cyst associated with subdural effusion and manifesting as headache and vomiting after minor head injury. Computed tomography disclosed a cystic lesion in the left middle cranial fossa and ipsilateral subdural effusion. Fundoscopic examination revealed papilledema. A small tear of the cyst wall was confirmed endoscopically. Fenestration of the cyst was performed under the operating microscope. Postoperative course was uneventful. The tear in the outer wall of an arachnoid cyst may suggest the mechanism of occurrence of subdural effusion associated with middle cranial fossa arachnoid cyst.