Imaging Hemifacial Spasm

Hemifacial spasm, a syndrome of unilateral facial nerve hyperactive dysfunction, is a severe and disabling condition that negatively impacts the quality of life of patients. Vascular compression of the facial nerve is the most common etiology of hemifacial spasm, but not all segments of the nerve are vulnerable to compression. The vulnerable segment begins at the pontomedullary sulcus medially and extends laterally until approximately 4 mm lateral to the facial nerve's detachment point from the brain stem. Importantly, and unknown to many neuroradiologists, the facial nerve is attached to the pons for approximately 1 cm along the undersurface of the pons, and most cases of vascular compression causing hemifacial spasm occur along this “attached” segment. Knowledge of the anatomy and vulnerable portions of the facial nerve is critical to correctly identify patients who are candidates for microvascular decompression, to locate the culprit arterial vessel, and to guide operative management.

Learning Objective: Recognize the imaging appearance of vascular compression of the susceptible portion of the facial nerve in patients presenting with hemifacial spasm.