Anatomic Variations Of The Anterior Portion Of The Circle Of Willis: An MR Angiography Study

:Variations of the Circle of Willis (CW) are not rare in population, some with clinical implications. The study was carried out with the aim to assess prevalence of variations of CW using magnetic resonance (MR) time-of-flight angiography. In this paper we focused only on the anterior portion of CW. Total of 1000 consecutively performed 1.5T cerebral MR angiographies were analyzed retrospectively, regardless of age, sex and basic pathology. Classic type of CW was found in 643 (64.3%) patients, 113 (11.3%) had variations of the anterior portion of CW, 244 (24.4%) of posterior, and 34 (3.4%) had associated anomalies. Unilateral hypoplasia of A1 segment of anterior cerebral artery (ACA) was found in 24 (2.4%), unilateral aplasia of A1 of ACA in 29 (2.9%), ayzgos ACA in 28 (2.8%), bihemispheric ACA in 14 (1.4%), triple A2 of ACA in 13 (1.3%) and fenestrations of ACA in 5 (0.5%) patients. The results of the survey are in line with data reported in other radiological and hystological studies. Clinical implications of these anatomical variations remain unclear, and require further investigation.