FACIAL-NERVE OUTCOME AFTER ACOUSTIC NEUROMA SURGERY - A STUDY FROM THE ERA OF CRANIAL NERVE MONITORING

The introduction of intraoperative cranial nerve monitoring in posteri or fossa surgery has greatly aided the surgeon in identification and a natomic preservation of cranial nerves. As a result,the long-term func tion of the facial nerve continues to improve after removal of acousti c neuroma. Herein, we report our long-term (1 year or greater) facial nerve outcome in 129 patients who underwent surgical removal of their acoustic neuromas with the aid of intraoperative neurophysiologic moni toring between 1986 and 1990. The facial nerve was anatomically preser ved in 99.2% of the patients, and 90% of all the patients had grade 1 or 2 facial nerve function 1 year after surgery. Long-term facial func tion was inversely correlated with the size of tumor (chi-squared, p < 0.02) and was not related to the side of tumor, the age and sex of th e patient, or the surgical approach. In a comparison among tumor group s matched for size, no statistically significant difference in facial nerve outcome between the translabyrinthine and retrosigmoid approache s was detected. The proximal facial nerve stimulation threshold at the end of surgical removal was predictive of long-term facial nerve func tion (analysis of variance, p < 0.02). At 1 year, 98% (87 of 89) of th e patients with electrical thresholds of 0.2 V or less had grade 1 or 2 facial nerve function compared with only 50% (8 of 16) of those with thresholds between 0.21 and 0.6 V. In the era of cranial nerve monito ring, patients can be better advised about long-term facial nerve outc ome after surgical intervention. Preoperatively, the size of the tumor is the most critical factor in predicting long-term facial function. Postoperatively, the proximal seventh nerve stimulation threshold at t he end of the surgical procedure can be used as one prognostic measure of long-term facial nerve function.