MANAGEMENT OF VESTIBULAR SCHWANNOMAS (ACOUSTIC NEUROMAS) - THE VALUE OF NEUROPHYSIOLOGY FOR EVALUATION AND PREDICTION OF AUDITORY FUNCTION IN 420 CASES

OBJECTIVE: From 1978 to 1993, 1000 vestibular schwannomas were operate d on at the Department of Neurosurgery at Nordstadt Hospital. The goal was to improve the chances of hearing preservation by recording audit ory brain stem responses (ABRs). ABRs can be used for preoperative cla ssification of cochlear nerve impairment and for prediction of the cha nces of hearing preservation. PATIENTS AND METHODS: In addition to the previously described audiometric testing, the patients underwent peri operative and intraoperative bilateral ABR recording at 100-dB condens ation and rarefaction click stimulation. The classification system of five types of ABRs, as presented before, is based on the presence and on the latencies of Waves I, III, and V, with a special emphasis on Wa ve III's representing the activity of the first brain stem nuclei with in the auditory pathway. According to an analysis of 420 preoperative ABRs, in case of a preoperative Type 1 or 2, the rate of hearing prese rvation is 80%. DISCUSSION: In the case of good clinical and audiometr ic hearing, a severely deteriorated ABR is mostly an indicator of seve re nerve compression and adhesion by the tumor. In view of subsequentl y reported experiences with intraoperative ABR monitoring, the value o f the presented system emphasizing the importance of Wave III is stres sed and discussed with other views in the literature. The criteria pre sented here are not designed for recognition of retrocochlear disease but aim for evaluation of the state of the auditory nerve and its pers pective. CONCLUSION: By the presented classification of ABR Types B1 t hrough B5, preoperative prediction of the likelihood of hearing preser vation is improved.