Arachnoid bands in hemifacial spasm: an overlooked etiology? Illustrative case.

BACKGROUND: Primary hemifacial spasm (HFS) is usually caused by arterial compression of the facial nerve at the root exit zone at the brainstem. Rarely, a purely venous compression is seen. However, arachnoid bands strangulating the facial nerve have not been recognized as a cause of hemifacial spasm.

OBSERVATIONS: The authors present a case of a 24-year-old female who had experienced HFS for 9 years. Endoscopic inspection of the root exit zone revealed no vascular compression but an arachnoid band strangulating the facial nerve. After cutting the band, the lateral spread response disappeared, and the patient was immediately spasm free after the surgery. Two years later, she was still doing well without any spasms.

LESSONS: This is the third patient in the authors' series of 535 patients who had no vascular conflict but rather a strangulation of the nerve by arachnoid bands. All patients have remained spasm free. To the authors' knowledge, no other group has reported arachnoid bands as an etiological factor of HFS so far.