REPORT FROM THE AMERICAN ACADEMY OF NEUROLOGY (AAN) ANNUAL MEETING, PHILADELPHIA PA, APRIL 26-MAY 3, 2014 – It has been suggested that circle of Willis variants may contribute to the pathogenesis of migraine as a result of decreased or more variable regional cerebral blood flow (Cucchiara et al. Med Hypotheses 2008;70:860-87).

This has been investigated in the Anatomy and Cerebral Hemodynamic Evaluation of Migraine (ACHE-M) controlled study of migraine patients with and without aura (Cucchiara et al. PLoS One 2013;8:e71007).

An incomplete circle of Willis on MR angiography was significantly more common in migraine with aura compared to controls (32% vs. 13%); while migraine without aura had intermediate results (21%). An incomplete circle of Willis was more common in males compared to females (79% vs. 59%). However, an analysis of 156 subjects found no significant differences in global or regional cerebral blood flow on perfusion MRI, although there was greater asymmetry in hemispheric cerebral blood flow in migraine patients. The authors speculated that circle of Willis variants may allow for relative ischemia during situations of increased metabolic demand.

As a follow-up to that study, Cucchiara and colleagues have now examined the relationship between circle of Willis variants, cerebral blood flow and white matter hyperintensities (WMH) (AAN 2014; abstract P6.199). A high WMH load was more common in migraine than controls (23% vs. 17%), although differences were not significant. Increased WMH were not generally associated with lower cerebral blood flow, but migraine patients with aura and a high WMH load did appear to have lower cerebral blood flow.

Two prior studies using MR angiography have also reported an association between an incomplete circle of Willis and migraine (Bugnicourt et al. Headache 2009;49:879-886; Cavestro et al. Can J Neurol Sci 2011;38:494-499). Further investigations are needed to determine if circle of Willis variants contribute to the increased risk of ischemic stroke in migraine patients.

Guest Reviewer: Dr. Daniel Selchen, Head of Neurology, St. Michael’s Hospital, Toronto, Canada