Effectiveness of C5 or C6-Cz assembly in predicting immediate post operative facial nerve deficit

Abstract

Intraoperative neurophysiology monitoring (IOM) is a valuable tool in cerebellopontine angle (CPA) surgeries posing risk to the cranial nerves. Transcranial electrical stimulation (TES) for cranial nerves has been performed in the last 7 years, for obtaining the facial nerve motor evoked potential (MEP), using either C3/C4-Cz or C3-C4 (or inverse) stimulating points, which have been correlated with facial nerve functional outcome. Intraoperative surgical and electrophysiological findings were documented prospectively. Patient files were reviewed for clinical data. We studied 23 patients undergoing CPA tumor resection using C5 or C6-Cz montage for TES, and were able to determine the correlation between facial nerve functional outcome and the amplitude drop of facial MEP above 50 %. Patients were evaluated for immediate facial nerve outcome and 6 months after the surgery. Follow-up was performed by structured telephone interviews with local physicians. The sensibility of the studied parameters was 92.8 % for amplitude drop of facial nerve MEP, with positive predictive value of 81.2 %. The absence of changes during IOM has shown a negative predictive value of 100 %. In this series, the used montage was effective in predicting new facial deficit.