Completeness of the circle of Willis and risk of ischemic stroke in patients without cerebrovascular disease

Introduction: We investigated circle of Willis (CoW) completeness in relation to the risk of future ischemic stroke in patients without prior cerebrovascular disease. Methods: We included 976 patients with atherosclerotic disease, but no previous TIA/stroke, from the Second Manifestations of ARTerial disease (SMART) study. All patients underwent MR angiography of the CoW. Cox regression was used to determine whether anterior CoW completeness (anterior communicating artery or A1 segments) and posterior CoW completeness (posterior communicating arteries or P1 segments) were related to future stroke, and whether CoW completeness influenced the relation between internal carotid artery (ICA) stenosis/occlusion and future stroke. Results: Thirty patients (3.1 %) had ischemic stroke after 9.2 ± 3.0 years of follow-up. Twenty-four patients (80 %) had anterior circulation stroke. An incomplete anterior CoW was related to future anterior circulation stroke (HR 2.8 (95 % CI 1.3–6.3); p = 0.01), whereas a one-sided and two-sided incomplete posterior CoW were not (HR 2.2 (95 % CI 0.7–7.1; p = 0.19) and 1.9 (95 % CI 0.6–5.9; p = 0.29), respectively). In stratified analyses, patients with an incomplete anterior CoW had the highest risk of future anterior circulation stroke when they also had a one-sided (HR 7.0 (95 % CI 1.3–38.2; p = 0.02)) or two-sided incomplete posterior CoW (HR 5.4 (95 % CI 1.0–27.8; p = 0.04). CoW completeness did not change the relation between asymptomatic ICA stenosis/occlusion and future ischemic stroke (p = 0.68). Conclusions: An incomplete anterior CoW combined with an incomplete posterior CoW is related to future anterior circulation stroke. CoW completeness has no large effect on the relation between asymptomatic ICA stenosis/occlusion and future stroke.