Lateral Spread Response in Hemifacial Spasm: Physiological Mechanisms, Intraoperative Utility, and Prognostic Significance.

Facial nerve compression by blood vessels near the brainstem can cause hemifacial spasm (HFS). There are two treatment options for this condition: botulinum toxin and surgical microvascular decompression (MVD). During microvascular decompression, the facial nerve is separated from the offending vessel, and intraoperative neuromonitoring in these patients demonstrates abnormal muscle response (AMR), which is known as the lateral spread response (LSR). Though the disappearance of lateral spread response is a hallmark of successful microvascular decompression, little information is available about its physiological origin and diagnostic utility. In the present review, we have attempted to address the aforementioned caveats about lateral spread response with an emphasis on the intraoperative utility and diagnostic role of this electrophysiological phenomenon.