Microvascular decompression (MVD) is a widely used surgical intervention to relieve the abnormal compression of a facial nerve caused by an artery or vein that results in hemifacial spasm (HFS). Various intraoperative neurophysiologic monitoring (ION) and mapping methodologies have been used since the 1980s, including brainstem auditory evoked potentials, lateral-spread responses, Z-L responses, facial corticobulbar motor evoked potentials, and blink reflexes. These methods have been applied to detect neuronal damage, to optimize the successful decompression of a facial nerve, to predict clinical outcomes, and to identify changes in the excitability of a facial nerve and its nucleus during MVD. This has resulted in multiple studies continuously investigating the clinical application of ION during MVD in patients with HFS. In this study we aimed to review the specific advances in methodologies and clinical research related to ION techniques used in MVD surgery for HFS over the last decade. These advances have enabled clinicians to improve the efficacy and surgical outcomes of MVD, and they provide deeper insight into the pathophysiology of the disease.

The main treatment for most patients with intramedullary spinal cord tumors is surgical resection. Intraoperative neurophysiological monitoring can be applied in this case to reduce the risk for the occurrence of postoperative neurological complications. In addition to motor-evoked, somatosensory-evoked potentials and the bulbocavernosus reflex, which are applied in various spinal surgery types, 'spinal cord mapping (SCM)' can be used for intramedullary spinal cord tumor surgery. Two examples are the dorsal column mapping before myelotomy to determine the electrophysiological midline, to attempt minimizing the postoperative dorsal column damage, and motor tract mapping to reduce the risk of motor-pathway damage during tumor removal. Our review explores the research published overseas regarding these two mapping methods, including technical aspects and key points in the mapping application. Although SCM has not yet been established in Korea, its application is expected to increase soon.

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Spinal cord cavernous angioma (SCAA) is a rare tumorous condition that can manifest various neurologic symptoms, and most lesions are needed to be removed surgically. However, since the SCAA is positioned intramedullary, the tumor resection could have a modest risk for the development of neuronal injury. Intraoperative neurophysiologic monitoring (IONM) has been widely accepted as an effective tool for detecting neuronal damage and predicting postoperative neurologic deterioration in intramedullary spinal cord tumor surgery. Here, we briefly report a representative case of SCAA surgery with IONM, which showed the different patterns of electrophysiologic change in each lower limb, followed by the relevant postoperative neurologic states. Based on this case, we could confirm the clinical significance of the application of IONM again.