Contralateral trigeminal nerve dysfunction as a false localizing sign in acoustic neuroma: a clinical and electrophysiological study.

A 49-year-old woman presented with right facial sensory impairment due to trigeminal nerve dysfunction caused by a contralateral acoustic neuroma. The mechanism of the falsely localizing trigeminal involvement is probably displacement and distortion of the brain stem by the large mass lesion and not increased intracranial pressure. A preoperative orbicularis oculi reflex study was abnormal and indicative of right trigeminal nerve dysfunction; after surgical removal of the tumor, the orbicularis oculi reflex study was normal. We conclude that a false localizing sign of trigeminal nerve dysfunction can occur rarely on the contralateral side in patients with large posterior fossa tumors, especially tumors arising from the cerebellopontine angle, and should be considered in the differential diagnosis of hemifacial sensory disturbance.