A comparative study of intraoperative findings and postoperative outcomes between atypical and typical hemifacial spasms

In most hemifacial spasm cases, the spasm initiates from the orbicularis occuli muscle and gradually spreads downwards to the orbicularis oris and buccinator muscles. Seldomly, the spasm might start from the orbicularis oris and buccinator muscles and develop upwards, which has been called as atypical hemifacial spasm (aHFS). Until now, little is known about its pathogenesis and the efficacy of microvascular decompression (MVD) surgery. We reviewed 1935 HFS cases undergoing MVD between 2007 through 2016. Among them, 15 were diagnosed as aHFS, whom were focused on. Their intraoperative findings and postoperative outcomes were compared with those typical hemifacial spasm (tHFS) cases. In the aHFS group, the conflict site was found in the root exit zone (REZ) in 12 (rostral 9, dorsal 2, and ventral 1) and in the cisternal segment in 3. In the tHFS group, the conflict site was found in the REZ in 1812 (rostral 6, caudal 1734, dorsal 12, and ventral 60) and in the cisternal segment in 108. The rostral REZ seemed to be the most frequent neurovascular conflict site in aHFS compared to the caudal REZ in tHFS (p < 0.05). Postoperatively, the effective rate of MVD was 93.3% in the aHSF group, while 96.3% in the tHSF group (p > 0.05). It was demonstrated that MVD may also lead to a satisfactory outcome for aHFS. Although the caudal REZ of the facial nerve is a frequent conflict site for most of the hemifacial spasm cases, the rostral side or cisternal segment of the facial nerve root should not be ignored while searching for the offending artery.