Abstract          Objectives: To evaluate and to describe the prevalence and pattern of Circle of Willis (CW), arterial variants and associated anomalies in noncontrast 3D-TOF-MRA in a random study group and to investigate whether any sex- or age-related differences could be found in circle morphology. Materials and Methods: In a descriptive study, 180participants (108 men and72 women); mean age, 68 years referred for neuroischemic study protocol from June 2015 to June 2016 were included in the study. Images were obtained with the sequence of spoiled gradient-recalled acquisition (SPGR) using a 1.5-tesla MR scanner (Achieve; Philips Medical Systems). Images were reviewed for CW anatomy and configuration. Observations and results: The prevalence of complete configuration of the circle was50 % in younger than 40 years and 45% in older than 40 years and is slightly higher in females than males. Complete anterior CW is more common with incidence of 75% in < 40 years and 65% in > 40 years individuals. The most common anterior circle variant is type A with a prevalence of 40-45% and the least common is type C. The most common posterior circle variant was type E with incidence of 24% in less than 40 years and 17% in >40 years. Overall, CW variants are slightly more common among the women in comparison to men. Conclusion: The morphological variations demonstrated by TOF-MRA in our study provide an important reference source for CW variations in the regional population. Incidence of associated anomalies, like aneurysm is comparable to that described in literature.

Keywords: Circle of Willis, variants, neuroischaemic, aneurysm.