Anatomic Variation and Hemodynamic Evolution of Vertebrobasilar Arterial System May Contribute to the Development of Vascular Compression in Hemifacial Spasm.

Background: Hemifacial spasm (HFS) is caused by vascular compression of the facial nerve. The definitive mechanism of offending vessel formation remains unclear. The aim of this study was to explore whether the anatomic and hemodynamic characteristics of the vertebrobasilar artery play a role in problematic vessel formation in HFS.

Methods: Imaging data of 341 patients with HFS who underwent microvascular decompression were reviewed retrospectively and compared with 360 control subjects. Hemodynamics of typical anatomic variations of the vertebral artery (VA) were analyzed using computational fluid dynamics software.

Results: Asymmetry of the left and right VAs was prevalent, and the left VA was the most dominant VA. A dominant VA was more prevalent in the HFS group than in the control group (P = 0.026). Left HFS had a significantly higher proportion of a left dominant VA, and right HFS had a significantly higher proportion of a right dominant VA (P < 0.001). Computational fluid dynamics models showed that angulation and tortuosity of vessels caused remarkable pressure difference between vascular walls of opposite sides. Dynamic clinical observations showed the mode of vessel transposition coincided with biomechanical characteristics.

Conclusions: Anatomic variations and hemodynamics of the vertebrobasilar arterial system are likely to contribute to vascular compression formation in HFS.