Circle of Willis Variants in Nepali Population Evaluated in TOF MR Angiography

A study from Nepal conducted by Sharma et al.(1) investigated anatomical variations of the Circle of Willis (CoW) in the Nepalese population using 3D Time-of-Flight Magnetic Resonance Angiography (TOF-MRA). Among 118 subjects, only 46.6% exhibited the typical CoW configuration, with the most common variation being the absence or hypoplasia of the posterior communicating artery (PCOM), particularly the right PCOM (13.6% of cases). The findings suggest that morphological variations in CoW are common in Nepal, similar to global studies. Notably, women were more likely to present variant configurations than men, though no age-related trends in CoW morphology were observed. A study similar to our was done by Kızılgöz et al.(2) in Turkish population. This study enrolled 867 patients who had undergone MR angiography (MRA) to assess the Circle of Willis (CoW). Using three-dimensional time-of-flight MRA images, the researchers re-evaluated vessel diameters across all CoW components and classified CoW variations. They also analyzed how vessel calibers and CoW integrity related to gender and age groups. The study had a higher proportion of female participants, with an average age of 48. Type A was the most frequent variation in both anterior (75.78%) and posterior (53.98%) circulations. In the anterior circulation, types G and H were also common, while types E and D were the second and third most frequent in the posterior CoW, respectively. Females generally had smaller calibers in both ICAs, both P1s, and the BA compared to males. In patients with a complete CoW, the diameters of the BA and both P1 segments were lower, while the left PCom diameter was significantly larger. There was a notable variation by sex and age in the distribution of complete, partially complete, and incomplete CoW configurations. These findings on vessel calibers in complete, partial, and incomplete CoWs suggest that further research is needed, and meta-analyses with other studies could provide insights into CoW morphology. A study from India by Naveen et al.(3) examined CoW configurations in a South Indian population using TOF-MRA on 300 subjects. They found that only 16.6% had a complete CoW, with the most frequent variation being hypoplasia or absence of PCOM, observed predominantly in the posterior circulation. Incomplete CoW configurations were more common in older adults, with significant differences between age and sex groups. These findings highlight the CoW's role as a collateral pathway and its potential impact on cerebrovascular health. In Norway, Hindenes et al.(4) studied CoW variants in a large population using 3D TOF-MRA. They identified 47 unique configurations, with the complete CoW variant found in only 11.9% of cases. The study revealed that missing posterior communicating arteries were most common and associated with older age, indicating reduced collateral capacity. No significant sex differences were noted. This study underscores the CoW's variability and the effect of aging on its structure, emphasizing the clinical significance of collateral pathways in cerebrovascular health. Another study done by Diljohn et al. in Trinidian population showed complete Circle of Willis (CoW) in 24.3% of participants, with a higher occurrence in younger individuals (≤45 years) and Afro-Trinidadians. No gender preference for a complete CoW was identified. The most frequent variations in the CoW were a hypoplastic anterior communicating artery (8.6%, n=13) and bilateral aplastic posterior communicating arteries (18.4%, n=28) in the anterior and posterior segments, respectively.