Intraoperative Identification and Location of Facial Nerve: Type of Facial Nerve Displacement—How to Use Monopolar Stimulator
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Intraoperative facial nerve monitoring (IOFNM) is a neurophysiological method whose main purpose is to inform the surgical team of the actual neural function—and, indirectly, of the position—of the facial nerve (N VII) so that the operative strategy can be consequently adjusted to avoid neural damage. The most commonly used—and therefore defined as “standard”—IOFNM techniques are direct electrical stimulation (DES) and free-running electromyography (EMG). DES allows for proper tracing of the course of N VII; the types of displacement reported have been correlated to tumor size and capsule adhesiveness in diverse studies. Functional changes in the activity of N VII—as detected by DES and EMG—also have a role in assessing postoperative functional prognosis. The technique of facial motor evoked potentials (FMEPs) is the most promising and latest frontier method in IOFNM as it surpasses most of the disadvantages of standard techniques.
KeywordsVestibular schwannoma/facial nerve Vestibular schwannoma/neurophysiological monitoring Vestibular schwannoma/direct electrical stimulation Vestibular schwannoma/electromyography Vestibular schwannoma/facial motor evoked potentials