Overall, the Icelandic study is in agreement with the previous studies, including the Cerebral Abnormalities in Migraine, an Epidemiological Risk Meschia et al Guidelines for the Primary Prevention of Stroke 3787 Analysis (MRI CAMERA) study, which found that, on the basis of MRI, migraineurs with aura had higher prevalence of subclinical infarcts in the posterior circulation (OR, 13.7; 95% CI, 1.7 112), with female migraineurs at an indepen- dent increased risk of white matter lesions (OR, 2.1; 95% CI, The mechanism and relevance of the migraine brain lesion association are unclear. In 1 cohort study based on MRA, there was a significant association between anatomi- cal variants of the circle of Willis and both migraines with- out aura (OR, 2.4; 95% CI, 1.5 3.9) and migraines with aura Unilateral posterior variants with basilar hypoplasia were statistically associated only with migraines with aura (OR, 9.2; 95% CI, 2.3 37.2).602 However, there was no statistical association between the presence of circle of Willis variants and ischemic lesions on MRI (OR, 1.5; 95% CI, 0.68 1.94), or with infratentorial lacunar lesions The relationship between these vascular anatomical variants in migraineurs to ischemic strokes is unclear. Once considered a disease of cerebral blood vessels, recent experimental and clinical data have indicated that migraine results from a complex interaction of several converging pathogenic factors. These include disturbance of cortical excitability, cortical spreading depression, meningeal inflam- mation, and activation of the trigeminovascular system.603 However, factors contributing to the increased risk of stroke with migraine remain elusive. Clinical-epidemiological stud- ies have suggested several mechanisms. 