A Case of Hemifacial Spasm Caused by Penetration of the Anterior Inferior Cerebellar Artery between the Facial Nerve and the Nervus Intermedius.

Hemifacial spasm (HFS) is a disorder that causes involuntary movements of the ipsilateral facial muscles because of vascular compression of the facial nerve. Microvascular decompression (MVD), a surgical procedure to detach the culprit vessel from the nerve is believed to be the most effective treatment for HFS. Nevertheless, in the rare case in which the vessel penetrates the nerve, positioning the vessel sufficiently far from the nerve is challenging. In this report, a case of right HFS in a 54-year-old man with an anterior inferior cerebellar artery that had penetrated the nerve fiber cleft between the facial nerve and the nervus intermedius is presented. In the present case, the patient achieved relief from spasm, and postoperative facial hemiplegia was prevented by splitting the cleft slightly, gently moving the vessel, and affixing it to the petrous part of the temporal bone. The anatomic relationship between the facial nerve and the offending vessel must be properly understood, which must be carefully manipulated in such "penetration-type" HFS cases.