Predictive Value of Preoperative and Intraoperative Neurophysiology in Evaluating Long-term Facial Function Outcome in Acoustic Neuroma Surgery

OBJECTIVE: To determine the role of neurophysiological preoperative and intraoperative parameters in providing prognostic information regarding facial nerve (FN) function at 1 year after translabyrinthine acoustic neuroma (AN) resection surgery. STUDY DESIGN: Prospective observational study in a tertiary referral center. Patients treated via translabyrinthine surgical approach for sporadic AN microresection between December 2015 and 2018. METHODS: Patients underwent preoperative (electroneurography-ENG, electromyography-EMG, and Blink Reflex-BR) and intraoperative (FN motor action potential-MAP and continuous EMG traces) neurophysiological studies. FN function was graded postoperatively at 1 year using House-Brackmann Scoring System. RESULTS: Sixty-two patients were included in the analysis. Mean age was 53+/-10 years and average tumor diameter was 23 +/- 9 mm. At 1 year a normal facial function was observed in 68% of patients. In the univariate analysis a pathologic BR, low FN MAP values and ratios, and the presence of pathological neurotonic tracing (A-trains) on continuous EMG were associated with a poor facial nerve function outcome at 1 year postoperatively. Pathological preoperative BR testing and intraoperative A-trains showed a statistical significance also in the multivariable analysis, regardless of tumor size. CONCLUSIONS: Preoperative pathological BR testing and A-train activity on intraoperative EMG are correlated with poor FN outcomes at 1 year postoperative. This may provide important prognostic information to both patients and treating neuro-otologists. In the future this may guide preoperative and postoperative patient counselling and possibly optimize timing of facial nerve reanimation in selected patients.