Evaluation of Circle of Willis Variations Using 1.5 Tesla Time-of-flight Magnetic Resonance Angiography

Objectives:The circle of Willis (COW) is an arterial ring located at the base of the brain that connects the internal carotid and vertebral arteries through anastomotic branches.This circle includes two anterior cerebral arteries (ACA) connected by the anterior communicating artery (AComA) in the anterior part; two posterior cerebral arteries (PCA) linked to the carotid system via the posterior communicating arteries (PCom), along with the basilar artery in the posterior part.Collateral circulation in the COW is important in maintaining adequate cerebral blood flow in cases of obstructive arterial diseases.This study aimed to reveal the frequency of each COW variation detected on magnetic resonance imaging (MRI) time-of-flight images.Methods: This retrospective study included of 410 adult patients who underwent brain MRI due to symptoms such as headache, dizziness, ormemoryloss.Anterior and posterior segments of the COW (A1, AComA, PCom, P1) were evaluated separately.Vessel segments with a diameter smaller than 1 mm were considered hypoplastic.Vascular diameters of the COW were measured through the axial plane, perpendicularly to the elongation of the artery and 3 mm from the vessel origin.When the vascular segment is too short, the middle part of the artery is measured.Results: Of the 410 individuals, 176 were male and 234 female, with a mean age of 41.212.7 years.A complete, symmetric COW was observed in 118 cases (28.8%).The most common variations were: -PCom hypoplasia: right 23.1%, left 18.6% -PCom aplasia: right 9.7%, left 7.6% -fetal PCA: unilateral 11.2%, bilateral 4.6% -azygos ACA: 0.7% -basilar artery fenestration: 0.7% -persistent trigeminal artery: 0.2%.There were no statistically significant differences in the prevalence of variation between sexes (p>0.05). Conclusion:COW exhibits significant anatomical variability between individuals.Awareness of these anatomical patterns is important in clinical decisionmaking, influencing treatment strategies and risk assessment.