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 nerve outcome in acoustic neuroma surgery. This is a retrospective case review of 116 consecutive procedures to remove acoustic neuromas using either a retrosigmoid or translabyrinthine approach.

STUDY DESIGN: Retrospective study.

SETTINGS: The Tertiary Referral Center at The California Ear Institute in Palo Alto, California.

PATIENTS: These were consecutive presenting patients with acoustic neuroma in the senior author's practice. Patients were not categorized into age, sex, race, or other demographic features.

INTERVENTION: All patients had acoustic neuromas detected via magnetic resonance imaging, and they underwent surgery 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.

RESULTS: The patients were categorized by postoperative facial nerve function evaluated a minimum of 6 months after surgical removal. Group I was composed of those patients with facial nerve grades of I or II. The median threshold stimulus voltage required to produce measurable facial nerve activity at the root entry zone (REZ) immediately after tumor removal in this group was 0.100 V. Patients in group II had postoperative facial nerve grades of III to VI. Median threshold stimulus in this group was 0.7250 V. The difference in median threshold stimulus voltage at the REZ after tumor removal between these two groups was found to be statistically significant in using the nonparametric Mann-Whitney U test.

CONCLUSIONS: The results of this study strongly support the continued use of intraoperative facial monitoring as a predictor of postoperative facial nerve outcome after acoustic tumor surgery.