[Eighth cranial neuritis difficult to differentiate from intracanalicular acoustic neurinoma on MRI: case report].

A patient with an enhancing, completely intracanalicular mass on MRI was presented. He had noticed progressive hearing loss in the left ear with tinnitus. Neurological examination revealed no abnormality except decreased hearing in the left ear. There were no other cranial nerve or cerebellar signs. An audiogram revealed profound hearing loss on the left ear with no ability of speech discrimination. Brainstem auditory evoked response was absent on the left. MRI enhanced with gadolinium-DTPA demonstrated an intracanalicular enhancing lesion on the left which was presumed to be an intracanalicular acoustic neurinoma. The patient underwent a left suboccipital craniectomy. The eighth cranial nerve appeared normal in the cerebellopontine angle cistern, and was swollen and discolored in the internal auditory canal. It was removed piecemeal. The patient remained deaf in the left ear postoperatively. Histopathologically, the lesion consisted of edematous nerve fiber and inflammatory cells, but no tumor cell was present within the specimen. The patient was diagnosed as having neuritis. The clinical time course of symptoms in our patient was not unusual for an acoustic neurinoma. It seems that the distinction between an intracanalicular acoustic neurinoma and other lesions cannot be made on basis of MR imaging alone. All available imaging modalities should be considered before a definitive surgical procedure is undertaken.