Hearing preservation and improvement of auditory brainstem response findings after acoustic neuroma surgery.

Among 9 patients with acoustic neuroma who underwent tumor removal by the middle cranial fossa approach during the past 5 years, 6 were selected for hearing preservation surgery which was successful in 5 cases (83.3%). For the prediction of success in hearing-preservation, factors related to hearing preservation, including preoperative findings of neurotological examination, were analyzed. Postoperative hearing threshold correlated significantly with wave V latency and I-V interpeak latency of preoperative auditory brainstem response (ABR) and the SP/AP ratio of preoperative electrocochleogram and postoperative facial palsy. The size of tumors and preoperative results of speech audiometry did not correlate with hearing results. Postoperative ABR findings were normalized within the observation period from 5 days to 10 months in 3 hearing-preserved patients. Possible mechanisms for improvement of ABR findings after the removal of acoustic neuroma are discussed.