A case of giant acoustic tumor which invaded into the vestibule was presented. The patient, 37-year-old, suffered profound hearing loss in his right ear for 5 years without vertigo and tinnitus. Audiogram showed a profound sensory hearing loss, over 120dB, in the right ear. The Caloric response of the right ear was highly depressed. The radiographic examinations of the temporal bone showed a giant tumor, about 5cm in diameter, in the right C-P angle. The internal acoustic canal was destroyed. The tumor was removed totally by both the translabyrinthine approach and the posterior fossa approach. Interestingly, it was found that the tumor invaded into the vestibule at the translabyrinthine operation. The utricular macula and the posterior crista were dislocated by the tumor and the lateral and the anterior cristae could not be identified. The origin of tumor was the inferior vestibular nerve. It was considered that the tumor invaded into the vestibule through the fundus of the internal acoustic canal. The pathological diagnosis was Antoni-A type neurinoma.
