Completely reversible, severe, acute neurological deterioration with an otherwise asymptomatic, huge intradiploic calvarial epidermal cyst.

A huge, intradiploic, right temporoparietal epidermal cyst was known to be present, unchanged in extent, for over 14 years in a 55-year-old man. Although extreme mass effect was demonstrated by computed tomography scans, results of the neurological examination were within normal limits. Treatment of nausea and vomiting after vestibular testing caused somnolence and an acute diencephalic-mesencephalic syndrome of tentorial herniation. However, only moderate amounts of analgesics and sedatives were given. These symptoms disappeared as the pharmacological sedative effect diminished. Thereafter the tumor was resected radically. Neuropathological examination confirmed an epidermal cyst. Results of the postoperative neurological examination were within normal limits.