The authors presented a case of a 46-year old male with a complaint of unilateral progressive sensorineural hearing loss and dizziness, diagnosed with fourth ventricle ependymoma. A Large unilateral acoustic neuroma compressing the cerebellum and brainstem was suspected at first, however results of detailed equilibrium tests including eye tracking test, optokinetic pattern test, caloric test and visual suppression test indicated bilateral lesions of the cerebellum and brainstem. MR images depicted a tumor mass from the fourth ventricle invading the bilateral cerebellum and brainstem, and the postoperative histological examination demonstrated typical findings of ependymoma. The possibility of a fourth ventricle ependymoma mimicking acoustic neuroma should be considered when we encounter cases with not only unilateral progressive sensorineural hearing loss and dizziness but also abnormal equilibrium test findings indicating bilateral cerebellum and brainstem lesions.
