To Örebro University

Background The Circle of Willis (CoW) is an arterial anastomotic circle located at the skull base thatmaintains collateral circulation in the brain. Variations in CoW anatomy are commonly presentin the general population. Absent or hypoplastic segments of the CoW have been linked to anincreased stroke risk.

Aim To determine whether CoW completeness is related to future ischemic stroke in the elderlypopulation after adjustment for relevant clinical risk factors.

Methods Consecutive patients that underwent computed tomography angiography (CTA) of the headbetween 2014-2015 (60 years or older) were included. CoW-integrity was determined on CTAimages. Patient journals were retrospectively examined for ischemic stroke events followingthe CTA. Cox proportional hazard regression analysis was performed to determine hazard forischemic stroke in patients with incomplete CoW.

Results 147 patients were included. The median follow-up time was 6.4 years (interquartile range 3.0years). 17 ischemic stroke events occurred during the follow-up period. Age (hazard ratio, HR1.10, p=0.03) and gender (HR 0.25, p=0.04) were statistically significant risk factors forischemic stroke. Complete anterior and posterior CoW was associated with lower strokehazards, however, the association was not statistically significant (HR 0.36, p=0.34 and HR0.67, p=0.45, respectively).

Conclusions No significant risk reduction could be observed for either complete posterior or anterior CoW.Sex and age were significant risk factors for ischemic stroke. Further research is necessary toinvestigate how CoW integrity influences stroke risk after adjustment for other risk factors.