Hemifacial spasm caused by vascular compression of the distal portion of the facial nerve associated with configuration variation of the facial and vestibulocochlear nerve complex.

It is generally accepted that hemifacial spasm (HFS) is caused by vascular compression at the root exit zone (REZ) of the facial nerve. We saw an HFS patient caused by vascular compression of the distal portion of the facial nerve associated with configuration variation of the facial-vestibulocochlear nerve complex. A 50-year-old female with left HFS was admitted to our hospital. Preoperative magnetic resonance image demonstrated no offending artery around the facial nerve at the nerve's REZ. Microvascular decompression of the left seventh cranial nerve was performed via a lateral suboccipital infrafloccular approach. The facial nerve arose more than 5 mm away from the vestibulocochlear nerve in the brain stem and both traveled apart toward the internal acoustic meatus in the cerebello-pontine cistern. No offending vessel was observed near the REZ of the facial nerve. The abnormal muscle responses of the mentalis muscle disappeared when the AICA was separated from the distal portion of the facial nerve. The patient was completely free of the HFS following surgery. The facial nerve arising away from the vestibulocochlear nerve in the brain stem is rare. It might influence the cause of HFS with compression of the distal portions of the seventh cranial nerve.