VALUE OF INTRAOPERATIVE THRESHOLD STIMULUS IN PREDICTING POSTOPERATIVE FACIAL-NERVE FUNCTION AFTER ACOUSTIC TUMOR RESECTION

Objective: The objective of this study was to determine the predictive value of intraoperative threshold stimulus and postoperative facial n erve outcome in acoustic neuroma surgery. This is a retrospective case review of 116 consecutive procedures to remove acoustic neuromas usin g either a retrosigmoid or translabyrinthine approach. Study Design: R etrospective study. Settings: The Tertiary Referral Center at The Cali fornia Ear Institute in Pale Alto, California. Patients: These were co nsecutive presenting patients with acoustic neuroma in the senior auth or's practice. Patients were not categorized into age, sex, race, or o ther demographic features. Intervention: All patients had acoustic neu romas detected via magnetic resonance imaging, and they underwent surg ery at the hands of the same neurootologic team, Drs. Nissen and Welsh . Main Outcome Measure: The electrophysiological monitoring reports of 81 cases of acoustic tumors. Measures in which intraoperative facial nerve monitoring was performed provided the data for this article. Res ults: The patients were categorized by postoperative facial nerve func tion evaluated a minimum of 6 months after surgical removal. Group I w as composed of those patients with facial nerve grades of I or II. The median threshold stimulus voltage required to produce measurable faci al nerve activity at the root entry zone (REZ) immediately after tumor removal in this group was 0.100 V. Patients in group II had postopera tive facial nerve grades of III to VI. Median threshold stimulus in th is group was 0.7250 V. The difference in median threshold stimulus vol tage at the REZ after tumor removal between these two groups was found to be statistically significant in using the nonparametric Mann-Whitn ey U test. Conclusion: The results of this study strongly support the continued use of intraoperative facial monitoring as a predictor of po stoperative facial nerve outcome after acoustic tumor surgery.