O3-E-20. Intraoperative cochlear nerve mapping by cochlear nerve action potential

Methods for intraoperative mapping of the cochlear nerve (CN) in surgery for acoustic neurinoma (AN) have not yet been established. We attempted intraoperative mapping of the cochlear nerve by cochlear nerve action potential (CNAP) with a new recording probe. The subjects were 10 patients who had undergone surgery for AN using a retrosigmoid approach. Three of the 10 patients had severe hearing impairment so that CNAP data could not be obtained. In six of seven patients with useful hearing acuity, CN could be identified during surgery. However, CNAP was obtained in the nerves adjacent to CN. We could identify CN by the difference in waveforms between CN and the adjacent nerves. The recording probe was appropriate for mapping, but was inappropriate for functional monitoring. In contrast, conventional electrodes were more suitable for functional monitoring, but were not suitable for mapping. The combination of these electrode types would greatly improve the accuracy of monitoring. We performed CNAP by monopolar and bipolar recording. In bipolar recordings, the signal to noise ratio was higher than that in the monopolar recordings. The combination of monopolar and bipolar recordings would also improve the accuracy of monitoring.