Meningioma of the internal auditory canal.

Meningiomas are the second most common tumor to involve the cerebellopontine angle (CPA), but controversy exists as to whether they can arise within the internal auditory canal (IAC) or whether involvement of the IAC occurs secondarily by extension from the CPA. This paper reports on a patient with an enhancing IAC meningioma that then grew and on subsequent scans was found to involve the CPA. This case demonstrates that these tumors can arise within the IAC and can grow out to involve the CPA. These findings are discussed within the context of meningioma tumor genetics and the histologic evidence for precursor cells in the IAC. The radiologic findings useful in distinguishing an acoustic neuroma from a meningioma are reviewed in the light of this case. While an enhancing mass projecting into the IAC is most often an acoustic neuroma, this radiologic findings is not pathognomonic.