Intraoperative Monitoring of the Facial Nerve during Microvascular Decompression for Hemifacial Spasm.

This review article discusses the clinical significance of intraoperative neurophysiological monitoring (IONM), provides recommendations for monitoring protocols, and considers the interpretation of results in microvascular decompression (MVD) for hemifacial spasm (HFS). The lateral spread response (LSR) is an important monitoring parameter during MVD. It helps to identify the responsible blood vessel and confirms its thorough decompression from the facial nerve. The disappearance of the LSR during surgery is associated with favorable clinical outcomes. Standard and revised monitoring protocols and the confirmation of LSR persistence and disappearance are also discussed. The blink reflex and other facial nerve monitoring modalities, such as free-running electromyography, facial motor evoked potentials, F-waves, and the Z-L response, are further considered.