MANAGEMENT OF VESTIBULAR SCHWANNOMAS (ACOUSTIC NEUROMAS) - THE VALUE OF NEUROPHYSIOLOGY FOR EVALUATION AND PREDICTION OF AUDITORY FUNCTION IN 420 CASES
C. Matthies et M. Samii, MANAGEMENT OF VESTIBULAR SCHWANNOMAS (ACOUSTIC NEUROMAS) - THE VALUE OF NEUROPHYSIOLOGY FOR EVALUATION AND PREDICTION OF AUDITORY FUNCTION IN 420 CASES, Neurosurgery, 40(5), 1997, pp. 919-929
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.