Preoperative differentiation between meningioma of the cerebellopontine angle and acoustic neuroma using MRI.

Preoperative differentiation between acoustic neuroma (AN) and meningioma of the cerebellopontine angle (CPA) is important in selection of the surgical approach, successful tumor removal, and preservation of hearing and facial nerve. We retrospectively reviewed the magnetic resonance imaging (MRI) findings associated with 30 meningiomas involving the CPA (MCPA) encountered between 1987 to 1991 at the University of California, San Francisco. Magnetic resonance imaging was critical in differentiating meningioma from AN in the CPA. Typical findings on MRI associated with MCPA, differentiating them from ANs, include: meningiomas are sessile, possessing a broad base against the petrous face, whereas ANs are globular; they are often extrinsic and eccentric to the internal auditory canal (IAC); when involving the IAC, they usually do not erode the IAC; MCPAs demonstrate hyperostosis of the subjacent bone and possess intratumoral calcification; they involve adjacent intracranial spaces and structures; and meningiomas are characterized by a distinctive dural "tail" extending away from the tumor surface. While any one finding may not be diagnostic by itself, taken together the constellation of these findings is strongly indicative of meningioma. In our experience, MRI with gadolinium enhancement was able to distinguish MCPA from AN in nearly every case.