Trilobed meningioma: ampulla of posterior semicircular canal, internal auditory canal, and cerebellopontine angle.

Meningiomas rarely arise from or remain limited to the temporal bone. When the diagnosis of temporal bone meningioma is made, it is mandatory to investigate the possibility of an intracranial component. Computerized axial tomography with contrast enhancement is of limited value in detecting small tumors adjacent to the temporal bone or within the internal auditory canal. If the computerized tomogram is normal, a positive contrast posterior fossa myelogram is indicated. The pitfall of depending solely upon computerized tomography to detect intracranial extension became clear in the evaluation of a patient found to have an unusual trilobed meningioma.