Intraoperative neuromonitoring for removal of large vestibular schwannoma: Facial nerve outcome and predictive factors

• Preservation of FN function is one major goal for large VS resection.
• INOM helps to identify facial nerve.
• INOM helps to increased rate of complete removal.
• Tumor size and INOM parameters are indicative factors for FN function.

BackgroundPreservation of facial nerve (FN) function is one of the major goals for resection of large vestibular schwannoma (VS) (≥30 mm). Little is known about the FN outcome and its predictive factors due to limited data.ObjectiveTo explore the predictive factors affecting FN outcome following resection of large VS.Methods106 Large VS patients underwent surgical resection from 2010 to 2012 via intraoperative neuromonitoring for FN preservation approach. Postoperative FN function evaluation was conducted at the time points of 3–7th day, 3rd month and at the end of the 2nd year. Correlation between tumor size, intraoperative parameters and FN function were examined.ResultsThe ratios of total and subtotal resection were 82.1% and 14.2%, respectively. Acceptable FN function was achieved in 78% patients. Patients with good FN function showed much smaller (P < 0.01) VS size than those of poor-FN function patients at 3–7th day, 3rd month and 2nd year. There was a significant correlation between facial motor evoked potential (FMEP) ratios and postoperative FN function at 3–7th day (r = −0.709, P < 0.001) 3rd month (r = −0.709, P < 0.001) and 2nd year (r = −0.750, P < 0.001). Maximal response amplitude (MRA) ratio was a supplementary indicator for train time in predicting both immediate and long-term FN function in patients with large VS.ConclusionIndicative factors of both immediate and long-term postoperative FN function in large VSs include tumor size, intraoperative train time, start to final FMEP ratios and proximal to distal MRA ratios.