Background and Objectives: The published literature highlights the fact that the integrity of the Circle of Willis has a direct impact on stroke outcome, especially in cases of distal internal carotid T occlusion. The aim of this study was to review the available data on the Circle of Willis configuration and thrombus location impact on patient outcome in cases of ischemic stroke. Materials and Methods: A systematic search according to PRISMA guidelines was performed in PubMed, Cochrane, and EMBASE databases to identify studies investigating the influence of Circle of Willis variants on ischemic stroke outcomes published up to March 2023. The manuscripts were reviewed by three researchers separately and scored on the quality of the research using the MINORS criteria. Results: After screening 157 manuscripts, 11 studies (n = 4643) were included. Circle of Willis integrity plays a vital role in stroke outcome, especially when T-form occlusions are present. Despite this, in the event of M1 occlusion Circle of Willis configuration does not play an important role. In cases of distal internal carotid artery occlusion, the presence of a fully developed contralateral A1 segment and anterior communicating artery is essential for a favorable stroke outcome. Conclusions: The preserved integrity of the Circle of Willis has great significance for collateral flow in the event of ischemic stroke and helps patients to achieve more favorable outcomes, as it determines the affected brain territory. The clinical outcome of the ischemic stroke appears to be significantly better if only one artery territory is affected, compared to two or more.
Keywords: anatomic variants; circle of Willis; stroke.