PREDICTION OF FACIAL-NERVE FUNCTION FOLLOWING ACOUSTIC NEUROMA RESECTION USING INTRAOPERATIVE FACIAL-NERVE STIMULATION

Methods of monitoring the facial nerve during posterior fossa surgery continue to evolve. In an effort to predict acute and final facial ner ve function following acoustic neuroma resection, the lowest current a pplied to the facial nerve at the brainstem necessary to elicit facial muscle response was measured using strain gauge and electromyographic facial nerve monitors. A retrospective analysis of 121 patients who h ad undergone acoustic neuroma surgery was performed. Sixty-five patien ts had intraoperative facial nerve monitoring and 44 had sufficient da ta for inclusion in this study. The acute and final facial nerve funct ions, according to the House-Brackmann classification, were assessed w ith regard to intraoperative stimulation-current thresholds. Nineteen of 20 patients who required 0.10 mA or less to elicit a facial muscle response had a House-Brackmann grade I facial nerve outcome. The upper limit of the 95% confidence interval of stimulation threshold for pat ients with a final grade I facial nerve function is 0.17 mA. All of th e patients in this study, with stimulation thresholds ranging up to 0. 84 mA, had a final grade III or better result. A poor outcome in our s eries, a final grade III facial nerve function, is best predicted by a poor acute result, specifically an acute grade VIA facial nerve funct ion, We suggest that it is possible to predict the facial nerve functi on based on intraoperative threshold testing.