Primary hemifacial spasm: anatomical insights.

Background: Primary Hemifacial Spasm (pHFS) is a disorder caused by compression of vessels on the root of the facial nerve. There has been conflicting evidence regarding the side of the face that is more frequently affected. Moreover, it has been found in several studies that women are afflicted by approximately twice as many as men.

Objectives: We reviewed the literature to explain HFS tendencies from an anatomical aspect. We wanted to see whether there are anatomical variations that can increase the risk of developing HFS or underlie its tendency to a specific gender and side of the face.

Methods and material: A PubMed search was done for the articles on "Hemifacial Spasm" published in English literature, and we selected the articles regarding the significant anatomical differences in HFS patients.

Results: AICA proximal branching pattern, highly originated PICA, VA dominancy, and VA deviation are among the predisposing anatomical variances. Overall, both sides of the face are equally affected in HFS. However, there are side preferences based on the causative vessels, which may be due to differences in the anatomical features of the left and right side vessels.

Conclusions: Various anatomical variations regarding posterior circulation can increase the risk of HFS. Recent evidence suggests whether there is no side dominance or a tendency exists toward the left side. There is no comprehensive explanation for precise reasons underlying the tendency of HFS to affect women. Evidence regarding anatomical variations of the posterior circulation comparing men and women with HFS is scarce, and further studies are required.