Hemifacial spasms caused by compression of the labyrinthine artery on the facial nerve in the internal auditory canal: a case report and review of the literature.

PURPOSE/

aimHemifacial spasm caused by compression of the facial nerve in the internal auditory canal is very rare, as only 10 preoperative cases have been confirmed. Hemifacial spasm caused by compression of the labyrinthine artery on the facial nerve in the internal auditory canal is exceptionally rare; no other cases have been reported. This is the first report of such a case, offering new understanding of the causes of hemifacial spasm and new guidance for the surgical treatment of refractory hemifacial spasm. CASE REPORT: We present a case of a 49-year-old Han female with hemifacial spasm who experienced involuntary twitching of the right facial area for more than 8 years. A facial nerve magnetic resonance imaging scan suggested that the root of the right facial nerve was close to the anterior inferior cerebellar artery. The patient underwent microvascular decompression at our hospital on 10 July 2024. During the operation, the root exit zone of the right facial nerve was explored first, and the anterior inferior cerebellar artery was cushioned with Teflon. Electrophysiological monitoring revealed that abnormal muscle response did not disappear. The cisternal portion of the facial nerve was explored more fully, and the labyrinthine artery was found to be in close proximity to it. Teflon was used as a cushion between the facial nerve and the labyrinthine artery, but the abnormal muscle response did not subside. Finally, it was discovered that the labyrinthine artery and its branches were compressing the facial nerve in the internal auditory canal. After the labyrinthine artery and its branches were separated from the facial nerve with Teflon, the abnormal muscle response disappeared completely. After surgery, the patient's facial twitching fully resolved, and no obvious complications, such as hearing loss or facial paralysis, were observed. Follow-up observation after 8 months revealed no recurrence of facial twitching.

conclusionTo our knowledge, no other cases of hemifacial spasm involving compression of the labyrinthine artery on the facial nerve in the internal auditory canal have been reported in literature. Neurosurgeons should understand from this rare case that not all hemifacial spasms are caused by compression of the root exit zone of the facial nerve, and that compression of the facial nerve of the cisternal portion segment and even in the internal auditory canal cannot be ignored. These conditions must be distinguished through neuroelectrophysiological monitoring. If abnormal muscle response does not completely disappear after decompression of the root exit zone of the facial nerve, the facial nerve needs to be examined throughout the whole intracranial segment, including the root exit zone, the cisternal portion, and the internal auditory canal. All vessels in contact with the facial nerve should be separated until abnormal muscle response is eliminated completely.