Direct Recording from Cochlear Nerve via a Ball-Electrode in Transtemporal Acoustic Neuroma Surgery

Background: Intraoperative monitoring (IOM) of the cochlear nerve function during acoustic neuroma surgery is employed to assist in preserving hearing. So far, Auditory Brainstem Response (ABR) is considered to be an optimal method for intraoperative monitoring in transtemporal approach. The aim of this study was to perform direct recording of the cochlear nerve action potential after resection of the tumor by using a ball-electrode and to evaluate the use of this method in predicting the postoperative hearing. The obtained data were compared to the simultaneous ABR results and to the postoperative hearing. Materials and Methods: In 2009, 38 patients have undergone acoustic Neuroma Surgery at the ENT University hospital, Wuerzburg. In 33 patients an intraoperative ABR as well as a direct measurement from the cochlear nerve using a ball electrode were performed. In 5 patients the postoperative hearing was predicted using the direct measurement at the cochlear nerve only. Results: The direct recording from the cochlear nerve gave very robust responses. Even in cases where ABR recording was not possible, the identification of clear cochlear nerve action potential could still be reached. Using the direct recordings from the cochlear nerve to predict the post operative hearing turned out to have a sensitivity of 100% and a specificity of 70%. Conclusions: These results show that intraoperative monitoring with direct recording from the cochlear nerve via a ballelectrode in transtemporal approaches offers a valuable method to predict the postoperative hearing. Further investigation will be made to provide additional information.