Proportion of Variant Anatomy of the Circle of Willis and Association with Vascular Anomalies on Cerebral CT Angiography

Abstract

Background and Purpose. There is a wide variation in the anatomy of the CW in different individuals and population groups. The purpose of this study was to determine the proportion of variant anatomy of the circle of Willis (CW) and associated anomalies in patients with suspected cerebrovascular disease referred for cerebral computed tomography angiography (CTA) in two tertiary hospitals in Kenya. Methodology. This was a cross-sectional descriptive study conducted on 94 patients referred for cerebral CTA at the Kenyatta and Nairobi hospitals from August 2017 to February 2018. MIP and 3D reformatted images were analyzed by two senior radiologists to determine the final configuration of the CW and presence of vascular pathology. Vessels with diameters <0.8 mm were considered to be absent or hypoplastic. Chen et al. classification was used to determine the final configuration of CW. Results. Complete CW was seen in 37.2% (37.7% vs. 36.6% in males and females, respectively, p=0.909). Type A variant was the commonest anterior variant at 78.7%. Type E variant was the dominant posterior variant at 41.5%. Fetal PCA was demonstrated in 25.5%, unilateral > bilateral fetal PCA. Aneurysms were seen in 24.5% of patients. ACoA aneurysms were commonest at 43.6%. AVMs were seen in 8.5% of patients. Azygous ACA, fenestration, and duplication of vessels and persistent TA were not demonstrated. There is no significant association between aneurysms/AVMs and CW configuration. Conclusion. The findings in this study demonstrate slight differences in the CW configuration. A higher proportion of complete anterior CW was seen in female patients. Type A anterior and type E posterior circulation variants were the commonest in both males and females. No significant association was demonstrated between CW configuration and occurrence of aneurysms/AVMs in this study. Various methods of classification of CW configuration have been proposed with no standardized method to date, thus the need for consensus building between neuroanatomists, neurologists, neurosurgeons, and neuroradiologists for ease of comparison between similar future studies on the CW.

Circle of Willis: anatomical variations of configuration. A magnetic resonance angiography study

“…Adult type circulation was found in 105 patients (83.3%), with fetal circulation identified unilaterally in 11.1% of cases, and bilaterally in 5.6% of cases, a finding that is congruent with literature studies [15,19,24]. In the evaluation of adult vs fetal type circulation, that relies on deciding whether the posterior communicating artery is larger than the precommunicating segment of the posterior cerebral artery, some studies cite a third variant called transitional, where the two arteries are identical in size; however, we did not take this option into consideration, as we considered that it can introduce bias due to the limits in accurately comparing the vessel diameters, where the imaging plane, resolution and scale, blood flow, and imaging software may influence the measurements.…”

Reclassifications of ischemic stroke patterns due to variants of the Circle of Willis

“…[8][9][10][11][12][13][14][15] Our findings on the frequency of fPCA are in accordance with most previous studies, which found fPCA in around 20-30% of cases. 9,[15][16][17][18][19] The higher frequency of fPCA on the right side found in our study was also reported by two earlier studies in populations with cerebrovascular diseases. 9,16 In line with earlier studies, we found a lower frequency of vCoW in the anterior circulation compared to the posterior circulation.…”

Variability of the Circle of Willis in North American Caucasian and Middle East Arabic Cohorts

“…The anatomical variability of the patterns of the circle of Willis in different ethnic and racial groups is frequently disputed by authors. Although some authors have found no evidence of differences in various populations [4], others describe certain prevalence of one vascular pattern over the other in studied cohorts [3] [5] [7]. Comparison of the data obtained by authors from the different populations shows that all segments of the cerebral arterial ring were well developed in 37.2% of patients in Kenya, 28.4% of individuals in Iran, and only in 14.5% of the studies group in France (Table 4).…”

“…The review of literature shows that the complete arterial ring develops only in 14.5% -37% of individuals, and vascular components of CW exhibit a wide range of anatomic variations [3] [4] [5] [6]. In their extensive study on 507 samples, Chen et al [4] classified variations of the anterior and posterior parts of the CW by twenty types based on unilateral and bilateral hypoplasia or aplasia of each contributing vessel.…”

“…For instance, the unilateral hypoplastic posterior communicating artery was observed in 14.5% of Caucasian and in 42.8% of Asian cohorts [6] [8]. The hypoplastic pre-anastomotic segment of the anterior cerebral artery (A1) was found in 11.44% of cases in the research hold in Kenya, and only in 2% of brain specimens taken in Morocco [3] [7]. Does this difference reflect a genetic divergence of studied cohorts and may it be extrapolated to the whole population?…”