Recent update of intraoperative neurophysiological monitoring during microvascular decompression surgery for hemifacial spasm

Hemifacial spasm (HFS) is due to the vascular compression of the facial nerve at its root exit zone (REZ). Microvascular decompression (MVD) for the facial nerve near the REZ is the best effective and curative treatment for HFS. In MVD for HFS, intraoperative neurophysiological monitoring (INM) has two purposes. The first purpose is the unique feature of MVD for HFS, which is to assess and optimize the effectiveness of the vascular decompression. The purpose is achieved through monitoring of abnormal facial nerve EMG that is called as lateral spread response and is also partially possible through Z-L response, facial F-wave and blink reflexes. The second purpose is to prevent postoperative hearing loss during MVD surgery, which is possible through INM of brainstem auditory evoked potentials. Through INM mentioned above, MVD can be developed as a more safe and effective treatment for HFS. Over the past 20 years, much progress has been archived in INM during MVD for HFS, and MVD can be developed as a more safe and effective treatment for HFS.