Intrapetrous epidermoid deforming the pantopaque cisternogram.

Pantopaque cisternography is now an established procedure for the diagnosis of mass lesions arising in, or extending into the cerebellopontine angle. Non-filling of the internal auditory canal, even if of normal dimensions, is, with rare exceptions, diagnostic of an intracanalicular acoustic neurinoma. A case is reported of an intrapetrous epidermoid excavating the internal ear, but not widening the meatus, which prevented filling of the canal at cisternography.