Intraoperative monitoring of the facial nerve : Vestibular schwannoma surgery

In vestibular schwannoma surgery, facial nerve injury with consecutive functional impairment is one of the most important complications. Intraoperative monitoring of facial nerve function has been developed in order to avoid this complication. Which methods for intraoperative monitoring have been developed? Which methods are in use today and what can they achieve in modern vestibular schwannoma surgery? This article provides an evaluation and summary of the literature, as well as a discussion of the methods and their ability to achieve the goals of intraoperative monitoring. Intraoperative functional monitoring aims to identify and map the facial nerve in the surgical field during surgery. It also aims to identify potentially damaging events and allow for intraoperative prognosis of functional outcome. Available methods are direct electrical stimulation, free-running electromyogram (EMG), facial nerve evoked potentials, and processed EMG. Identification and mapping of the facial nerve in the surgical field can be reliably achieved by direct electrical stimulation; potentially dangerous events can be identified in real time by the free-running EMG and the processed EMG, and almost in real time by facial nerve evoked potentials. Intraoperative prognostics are hampered by false-positive results with all available methods and have limited reliability.