LAUSR

Facial nerve motor evoked potentials (FNMEP) are an important adjunct to facial nerve monitoring in cerebellopontine angle (CPA) tumorectomy. Numerous studies have shown a high specificity and moderate sensitivity in predicting immediate postoperative facial nerve function as well as long term facial nerve function when FNMEPs are evaluated (Bovo et al. 2021; Hong et al. 2020; Matthies et al. 2011; Song et al., 2018; Tawfik et al. 2019). When acquired, especially for resections of large tumors, FNMEPs are advantageous over traditional spontaneous electromyography (s-EMG) and direct nerve stimulation (DNS) since they can evaluate the entire length of the nerve in real-time before the nerve is encountered intraoperatively. Where s-EMG will only activate if the nerve is irritated and the DNS will only acquire a compound muscle action potential (CMAP) when the nerve is in the vicinity of the stimulation device (Song et al., 2018). Acquiring FNMEPs can be technically challenging compared to acquiring MEPs from limb muscles. This is partly due to the proximity of the branches of the facial nerve in the face relative to the stimulation electrodes. Taniguchi et al. (1993) describes needing multipulse high-frequency stimulation to activate an MEP in an anesthetized patient. Building on this principle, Dong et al. (2005) and Sarnthein et al. (2013) discuss using a single pulse stimulation to ensure activating a centrally conducted CMAP versus a peripherally conducted CMAP. Both groups show that a centrally conducted CMAP