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

Proportion of Variant Anatomy of the Circle of Willis and Association with Vascular Anomalies on... Hindawi Radiology Research and Practice Volume 2019, Article ID 6380801, 7 pages https://doi.org/10.1155/2019/6380801 Research Article Proportion of Variant Anatomy of the Circle of Willis and Association with Vascular Anomalies on Cerebral CT Angiography 1 2 1 Roy Munialo Machasio , Rose Nyabanda, and Timothy Musila Mutala University of Nairobi, Department of Diagnostic Imaging and Radiation Medicine, Kenya Kenyatta National Hospital, Kenya Correspondence should be addressed to Roy Munialo Machasio; rmachasio@gmail.com Received 5 February 2019; Revised 13 May 2019; Accepted 15 May 2019; Published 16 June 2019 Academic Editor: Paul Sijens Copyright © 2019 Roy Munialo Machasio et al. is Th is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Background and Purpose. eTh re is a wide variation in the anatomy of the CW in different individuals and population groups. eTh 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. er Th e is no significant association between aneurysms/AVMs and CW configuration. Conclusion. eTh findings in this study demonstrate slight dieff rences 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. 1. Introduction and stroke development [7–11]. A complete CW configura- tion has also been associated with reduced risk of intracranial The circle of Willis (CW) is an important anastomotic hemorrhage following intravenous thrombolysis in patients arterial polygon at the base of the brain that connects the with ischaemic stroke [12]. Persistent embryonic carotid- carotid and vertebrobasilar systems [1–3]. It is an essential vertebrobasilar anastomosis such as hypoglossal, proatlantal, route for collateral supply of blood to the brain in cases otic, and persistent trigeminal arteries are extremely rare of occlusionineither system[4, 5]. CWvariants include occurring in about 0.1%-0.6% of the general population [13]. fenestration, duplication, hypoplasia, or agenesis [6]. These CT angiography (CTA) is a fast reliable noninvasive method variants influence the cerebral blood flow hemodynamics for evaluation of the circle of Willis as well as other intracra- with influence on vascular territories, pathophysiology of nial arteries and aneurysms with high sensitivity and speci- cerebral arterial remodeling, aneurysm formation/rupture, cfi ity comparable to gold standard catheter angiography [14]. 2 Radiology Research and Practice Table 1: Percentage distribution of complete vs incomplete CW in males vs female patients. PERCENTAGE DISTRIBUTION OF CW CONFIGURATION GENDER COMPLETE INCOMPLETE MALE 37.7% (𝑛=20)62.3%(𝑛=33 ) FEMALE 36.6% (𝑛=15)63.4%(𝑛=26 ) COMBINED(MALE AND FEMALE) 37.2% (𝑛=35)62.8%(𝑛=59 ) AGE DISTRIBUTION Various methods have been proposed for classification of the morphology of the CW due to complex anterior and posterior circulation variations [1, 15–17]. Chen et al. 20 classified variations in both anterior and posterior CW from A-J[18,19].For the purposes ofthis study, Chen et al. classification was used due to its simplicity as compared to the other methods. The goal of the current study was to establish the propor- tion of variant anatomy of the CW and associated anomalies in patients with suspected cerebrovascular disease referred 1_10 11_20 21_30 31_40 41_50 51_60 61_70 71_80 81_90 91_100 for cerebral CTA in two tertiary hospitals in Kenya. AGE RANGE (YEARS) Figure 1: Age distribution of patients referred for cerebral CTA. 2. Materials and Methods This was a cross-sectional descriptive study carried out on patients referred for cerebral CTA at Kenyatta National Hos- 3. Results pital and Nairobi Hospital, both located in Nairobi County, Kenya. Male patients accounted for 56.4% while 43.6% were female CT image acquisition was done by SIEMENS SOMATOM patients with and approx. male to female ratio of 1:1. den fi ition AS +128 and PHILLIP’S BRILLIANCE 64 SLICE at The age distribution of patients referred for cerebral CTA Kenyatta and Nairobi hospitals, respectively. is depicted in Figure 1. Nonenhanced scans were acquired first to demonstrate Majority of patients were referred for cerebral CTA due to hemorrhage or calcification. clinically suspected intracranial hemorrhage accounting for 80 mls of LOCM (300mg/ml) via pump injector at 30.85%. Other clinical indications included suspected AVMs, injection rate of 5mls/second through an antecubital vein aneurysms, cerebral sinus thrombosis, stroke, trauma, and cannula (at least gauge 20) with a delay time of 7 seconds was tumor. used for acquisition of images in adult patients at Kenyatta National Hospital. 20 mls saline push before contrast administration, fol- 4. Proportion of Complete vs. Incomplete lowed by 60 mls of LOCM at an injection rate of 4-5 mls/s via Circle of Willis pump injector and 30 mls of saline chase with a scan delay time of 4.2 seconds, was used at Nairobi Hospital. A complete CW was seen in 37.2% of the patients with no For young children and infants, a 22- or 24-gauge IV statistically significant difference between males and females catheter was used and LOCM used at an injection rate of 2 (p=0.9) as shown in Table 1. mls/second. Figure 2 depicts a patient with complete circle of Willis in A total of 94 patients (53 males and 41 females) referred our study. for cerebral CTA at Kenyatta National Hospital and Nairobi Hospital from August 2017 to February 2018 were included. 5. Anterior and Posterior Circulation Variants MIP and 3D cerebral CTA images were analyzed for anatomic variants and pathology. A cut-off value 0.8 mm vessel diam- Type A variant accounted for 78.7% of the anterior circulation eter was used. Any vessel less than 0.8 mm was considered variants and was signicfi antly higher in females than male hypoplastic/absent. Final configuration and pathology were patients (p=0.016) as demonstrated in Table 2. confirmed by 2 senior radiologists. Patient’s age, gender, Figure 3 demonstrates a patient with combined type A anatomic variants of the circle of Willis, and presence of anterior and type E posterior circulation variants. aneurysms and AVMs were recorded in the patient data sheet. Statistical analysis using SPSS version 20.0 was done to Type E posterior circulation variant was the commonest determine association between the variants with aneurysms seen accounting for 41.5% of the posterior circulation variants and arteriovenous malformations. P value was set at 0.05. (Table 3). NUMBER OF PATIENTS Radiology Research and Practice 3 Table 2: Anterior circulation variant percentage distribution. ANTERIOR CW FREQUENCY (IN BOTH MALE AND FEMALES) FREQUENCY IN MALES FREQUENCY IN FEMALES TYPEA 78.7% (n=74) 69.8% (n=37) 90.2% (n=37) TYPE B 0% (n=0) TYPE C 1.1% (n=1) TYPE D 4.3% (n=4) TYPE E 0% (n=0) TYPE F 0% (n=0) TYPE G 4.3% (n=4) TYPE H 11.7% (n=11) TYPE I 0% (n=0) TYPE J 0% (n=0) Figure 2: Axial cerebral CTA MIP image showing a complete CW Figure 3: Axial MIP image showing combined type A anterior configuration. circulation variant and type E posterior circulation variant. Table 3: Proportion of posterior circulation variants. 7. Complete Posterior Circulation POSTERIOR CW FREQUENCY Variants (TYPES A-C) TYPE A 27.7% (26) A complete posterior CW configuration was seen in 39.4% TYPE B 4.3% (4) (39.6% vs. 39% in males and females, respectively, p=0.953). TYPE C 7.4% (7) TYPE D 4.3% (4) TYPE E 41.5% (39) 7.1. Adult Congfi uration of the Posterior Cerebral Arteries. There was a signicfi antly higher proportion of adult PCA TYPE F 2.1% (2) configuration in females than males (95%vs 81% p=0.044). TYPE G 7.4% (7) TYPE H 0% (0) TYPE I 0% (0) 8. Fetal PCA TYPE J 5.3% (5) Fetal PCA (Figure 4) was seen in 25.5% (28.3% vs. 22.0% in males and females, respectively, p=0.484). 6. Complete Anterior Circulation 9. Presence of Aneurysms and Location Variants (TYPES A-F) Aneurysms were seen in 24.5% of the patients referred for A complete anterior CW configuration was seen in 84%. The cerebral CTA (Table 4). proportion of this configuration was significantly higher in Figure 5 demonstrates a saccular aneurysm involving the females than males (92.7% vs. 77.4%, p=0.044). ACoA. 4 Radiology Research and Practice Figure 5: 3D cerebral CTA showing a saccular aneurysm at the ACoA. Figure 4: Axial cerebral CTA image showing bilateral fetal PCA with right P1 segment aplasia. Table 4: Distribution of intracranial aneurysms. Location of aneurysms ACOA 10 43.60% MCA 5 21.70% ICA 5 21.70% Other vessels than 3 13.00% Figure 6: 3D cerebral CTA image showing an AVM with feeding artery arising from the left MCA. 10. Association of CW Configuration and Aneurysms There was no association between CW configuration and Variations in the CW configuration have been associated presence of aneurysms as shown in Table 5. with cerebrovascular diseases [20, 21]. Various methods have been proposed for classification of 11. Presence of Cerebral variant anatomy of CW. The classification of CW configura- tion in this study is based on the Chen et al. classification Arteriovenous Malformations which classified anterior and posterior variants into 10 groups AVMs were seen in 8 (8.5%) of patients undergoing cerebral (A-J) [18, 19]. CTA (Figure 6). No association was found between CW The proportion of patients with complete CW configura- configuration and presence of AVM (P=0.987). tion was 37.2% (n=35). This was slightly higher in males than Fenestrations, duplications, azygous ACA, and persistent females: 37.7% vs. 36.6%. The findings in the current study TA were not observed in this study. are consistent with previous studies which have demonstrated a prevalence of between 12.24%-60% [19, 22]. An MRA- TOF study by Chuanya Qiu et al. on 2246 healthy Chinese 12. Discussion male population showed a lower prevalence of complete CW Previous anatomic, CTA, and MRA studies have demon- at 12.24% [4]. In contrast, an Egyptian MRA-TOF study strated significant variations in the configuration of the CW by Mohammed Abdelatif et al. on 180 patients with no in various population groups. manifestations of cerebrovascular disease showed a higher The purpose of this study was to determine the propor- prevalence of complete CW in 46.7% [23]. In our study, patients with cerebrovascular diseases referred for cerebral tion of variant anatomy of the circle of Willis (CW) and associated anomalies in patients with suspected cerebrovas- CTA were included unlike the above two MRA-TOF studies cular disease referred for cerebral CTA in 2 tertiary Kenyan which were conducted on patients with no manifestations hospitals. No similar studies on the CW configuration have of cerebrovascular disease. The findings in the current study been done in Kenya. could thus be attributed to the difference in the study Radiology Research and Practice 5 Table 5: Presence and number of aneurysms in complete and incomplete CW. Circle of WILLS anatomy Total Pvalue Characteristics Incomplete Complete Presence of Aneurysm No 71(75.5%) 43(72.9%) 28(80.0%) 0.438 Yes 23(24.5%) 16(27.1%) 7(20.0%) Number of Aneurysms 1 Aneurysm 18(78.3%) 12(75.0%) 6(85.7%) 0.567 More than 1 Aneurysm 5(21.7%) 4(25.0%) 1(14.3%) population, technique used, racial differences, and the lower was seen in 24.5%. Unilateral fetal PCA was more common than bilateral fetal PCA. 12.8% were right sided, 10.6% left sample size used in this study. An incomplete CW configuration was seen in 62.8% of sided, and 5.6% bilateral fetal PCA. patients, 62.3% in males versus 63.4% in females. Previous These findings are similar to a publication by Dimmick SJ studies have demonstrated a correlation between an incom- Faulder et al. which show a prevalence of 15%-32% for fetal plete CW and stroke severity and prognosis [10, 24]. PCA with bilateral fPCA at 8%, right sided at 10%, and left According to the Chen et al., classification type A-F sided fPCA at 10% [13]. Fetal PCA has been found to increase anterior variants are considered to be complete [18]. In our the extent and severity of anterior circulation stroke as well study, a complete anterior CW was seen in 84% (n=79). A as aneurysm formation [11, 31]. complete anterior CW was significantly higher in female than In the current study, aneurysms were seen in 24.5% male patients (92.7% vs. 77.4%, p=0.04). The prevalence of (n=23) of patients referred for cerebral CTA. 69.6% of the complete anterior CW in this study was higher than an MRA- aneurysms were located in the anterior CW while 4.3% were located in the posterior CW. 78.3% of patients had one TOF study by Sherif Mohamed Zaki et al. on 100 patents with no evidence of cerebrovascular disease which showed aneurysm while21.7% had morethan 1 aneurysm. a prevalence of 66% [25]. The finding in our study was also 26.1% (n=6) were located in other vessels other than higher than an MRA-TOF study by Shartri J et al. on 513 the CW. The prevalence of aneurysms in this study is lower adults without cerebrovascular disease which demonstrated a than that in an earlier Kenyan study by Chepsiror et al. complete anterior CW in 64.3% [26]. The higher prevalence based on conventional angiography which showed a higher of a complete anterior CW in our study could be due to higher prevalence of aneurysms at 40.9% and anterior circulation spatial resolution of CTA as compared to MRA, sample size aneurysms at 95.2% [32]. The study by Chepsiror et al. differences, and racial differences. was done on 88 patients with suspected cerebrovascular The commonest anterior circulation variant was type A disease who were referred for conventional angiography in variant accounting for 78.7% (n=74). This configuration was the two tertiary hospitals in Kenya. The difference in general seen in 69.8% (n=37) and 90.2% (n=37) of males and females, prevalence of aneurysms in the two studies could be due respectively. This finding is similar to studies done by Naveen to the higher sensitivity of conventional angiography for SR et al. and Dr. Arjun Bhaddur et al. which showed type A aneurysm detection. variant being the most common anterior circulation variant In the current study, ACoA aneurysms were the com- [27, 28]. monest at 43.6% (n=10). Type E posterior variant has been associated with 21.7% were located in the MCA, 21.7% were located in increased risk of ischaemic stroke [8]. This variant is of the ICA, and 13% were seen in other vessels than the CW. importance to surgeons and neurologists in the evaluation These findings are similar to a multimodality study on size of patients with intracranial tumors, traumatic injuries, and andlocation ofrupturedintracranial aneurysms by Young cardiovascular complications [29]. Gyun et al. which showed that a majority of aneurysms were In our study, type E posterior circulation variant was located in the ACoA [33]. These study findings are, however, the commonest posterior circulation variant accounting for in contrast to a conventional angiographic study on pattern 41.5%. This study finding is similar to findings on an MRA- of cerebrovascular disease in Kenyatta and Nairobi hospitals TOF study by Reddy Ravikanth et al. which demonstrated a doneby Chepsiror etal. which showed 30.6% atICA-PCoA, predominance of type E posterior circulation at 53% [30]. ACoA 22.2%, and MCA bifurcation 13% [32]. A cerebral CTA study done by Zhang Ning Jin et al. AVMs were seen in 8.5% (n=8) in the current study. on Chinese population with family history of stroke showed 62.5% (n=5) had incomplete CW while 37.5% (n=3) had a dominance of type E posterior variant with a prevalence of complete CW configuration. 52.3% [4], which is higher than the current study. The slight These study findings are similar to an earlier Kenyan conventional angiographic study by Chepsiror et al. which difference in prevalence of type E posterior variant could be due to racial and sample size differences. showed a prevalence of 8% [32]. In the current study, fetal PCA was seen in 30.9% (n=29). Association between duplication and fenestration of Complete PCA was demonstrated in 6.4% while partial PCA intracranial arteries with aneurysmal formation has been 6 Radiology Research and Practice documented in previous studies [13, 34]. Fenestration and Data Availability duplication of CW were not observed in our study. Previous Original data can be accessed upon request. publication by Dimmick SJ Faulder et al. has shown a low prevalence for duplications and fenestrations in angiographic studies of 0.058% [13]. A similarly low prevalence of anterior Disclosure circulation fenestration at 0.48% was demonstrated in a study This manuscript was submitted to the University of Nairobi as by Roger M et al. on 411 patients undergoing cerebral CTA [35]. part of fulfillment for master’s degree in diagnostic radiology. In the study by Roger M et al., patients with intracra- nial pathology such as subarachnoid hemorrhage, stroke, Conflicts of Interest tumor, and aneurysms were excluded from the study. In a previous Kenyan cadaveric study by Hassan Said et al. on The authors declare that there are no conflicts of interest 36 adult brains, fenestration and duplication of ACoA were regarding the publication of this manuscript. seen in 26% and 13%, respectively [36]. Another study by Dhanalakshmi V et al. on 50 adult cadaveric brains showed References a relatively lower prevalence of duplications and fenestration of the ACoA at 8% and 4%, respectively [37]. The absence [1] S. Kathuria, L. Gregg, J. 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Proportion of Variant Anatomy of the Circle of Willis and Association with Vascular Anomalies on Cerebral CT Angiography

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Hindawi Radiology Research and Practice Volume 2019, Article ID 6380801, 7 pages https://doi.org/10.1155/2019/6380801 Research Article Proportion of Variant Anatomy of the Circle of Willis and Association with Vascular Anomalies on Cerebral CT Angiography 1 2 1 Roy Munialo Machasio , Rose Nyabanda, and Timothy Musila Mutala University of Nairobi, Department of Diagnostic Imaging and Radiation Medicine, Kenya Kenyatta National Hospital, Kenya Correspondence should be addressed to Roy Munialo Machasio; rmachasio@gmail.com Received 5 February 2019; Revised 13 May 2019; Accepted 15 May 2019; Published 16 June 2019 Academic Editor: Paul Sijens Copyright © 2019 Roy Munialo Machasio et al. is Th is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Background and Purpose. eTh re is a wide variation in the anatomy of the CW in different individuals and population groups. eTh 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. er Th e is no significant association between aneurysms/AVMs and CW configuration. Conclusion. eTh findings in this study demonstrate slight dieff rences 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. 1. Introduction and stroke development [7–11]. A complete CW configura- tion has also been associated with reduced risk of intracranial The circle of Willis (CW) is an important anastomotic hemorrhage following intravenous thrombolysis in patients arterial polygon at the base of the brain that connects the with ischaemic stroke [12]. Persistent embryonic carotid- carotid and vertebrobasilar systems [1–3]. It is an essential vertebrobasilar anastomosis such as hypoglossal, proatlantal, route for collateral supply of blood to the brain in cases otic, and persistent trigeminal arteries are extremely rare of occlusionineither system[4, 5]. CWvariants include occurring in about 0.1%-0.6% of the general population [13]. fenestration, duplication, hypoplasia, or agenesis [6]. These CT angiography (CTA) is a fast reliable noninvasive method variants influence the cerebral blood flow hemodynamics for evaluation of the circle of Willis as well as other intracra- with influence on vascular territories, pathophysiology of nial arteries and aneurysms with high sensitivity and speci- cerebral arterial remodeling, aneurysm formation/rupture, cfi ity comparable to gold standard catheter angiography [14]. 2 Radiology Research and Practice Table 1: Percentage distribution of complete vs incomplete CW in males vs female patients. PERCENTAGE DISTRIBUTION OF CW CONFIGURATION GENDER COMPLETE INCOMPLETE MALE 37.7% (𝑛=20)62.3%(𝑛=33 ) FEMALE 36.6% (𝑛=15)63.4%(𝑛=26 ) COMBINED(MALE AND FEMALE) 37.2% (𝑛=35)62.8%(𝑛=59 ) AGE DISTRIBUTION Various methods have been proposed for classification of the morphology of the CW due to complex anterior and posterior circulation variations [1, 15–17]. Chen et al. 20 classified variations in both anterior and posterior CW from A-J[18,19].For the purposes ofthis study, Chen et al. classification was used due to its simplicity as compared to the other methods. The goal of the current study was to establish the propor- tion of variant anatomy of the CW and associated anomalies in patients with suspected cerebrovascular disease referred 1_10 11_20 21_30 31_40 41_50 51_60 61_70 71_80 81_90 91_100 for cerebral CTA in two tertiary hospitals in Kenya. AGE RANGE (YEARS) Figure 1: Age distribution of patients referred for cerebral CTA. 2. Materials and Methods This was a cross-sectional descriptive study carried out on patients referred for cerebral CTA at Kenyatta National Hos- 3. Results pital and Nairobi Hospital, both located in Nairobi County, Kenya. Male patients accounted for 56.4% while 43.6% were female CT image acquisition was done by SIEMENS SOMATOM patients with and approx. male to female ratio of 1:1. den fi ition AS +128 and PHILLIP’S BRILLIANCE 64 SLICE at The age distribution of patients referred for cerebral CTA Kenyatta and Nairobi hospitals, respectively. is depicted in Figure 1. Nonenhanced scans were acquired first to demonstrate Majority of patients were referred for cerebral CTA due to hemorrhage or calcification. clinically suspected intracranial hemorrhage accounting for 80 mls of LOCM (300mg/ml) via pump injector at 30.85%. Other clinical indications included suspected AVMs, injection rate of 5mls/second through an antecubital vein aneurysms, cerebral sinus thrombosis, stroke, trauma, and cannula (at least gauge 20) with a delay time of 7 seconds was tumor. used for acquisition of images in adult patients at Kenyatta National Hospital. 20 mls saline push before contrast administration, fol- 4. Proportion of Complete vs. Incomplete lowed by 60 mls of LOCM at an injection rate of 4-5 mls/s via Circle of Willis pump injector and 30 mls of saline chase with a scan delay time of 4.2 seconds, was used at Nairobi Hospital. A complete CW was seen in 37.2% of the patients with no For young children and infants, a 22- or 24-gauge IV statistically significant difference between males and females catheter was used and LOCM used at an injection rate of 2 (p=0.9) as shown in Table 1. mls/second. Figure 2 depicts a patient with complete circle of Willis in A total of 94 patients (53 males and 41 females) referred our study. for cerebral CTA at Kenyatta National Hospital and Nairobi Hospital from August 2017 to February 2018 were included. 5. Anterior and Posterior Circulation Variants MIP and 3D cerebral CTA images were analyzed for anatomic variants and pathology. A cut-off value 0.8 mm vessel diam- Type A variant accounted for 78.7% of the anterior circulation eter was used. Any vessel less than 0.8 mm was considered variants and was signicfi antly higher in females than male hypoplastic/absent. Final configuration and pathology were patients (p=0.016) as demonstrated in Table 2. confirmed by 2 senior radiologists. Patient’s age, gender, Figure 3 demonstrates a patient with combined type A anatomic variants of the circle of Willis, and presence of anterior and type E posterior circulation variants. aneurysms and AVMs were recorded in the patient data sheet. Statistical analysis using SPSS version 20.0 was done to Type E posterior circulation variant was the commonest determine association between the variants with aneurysms seen accounting for 41.5% of the posterior circulation variants and arteriovenous malformations. P value was set at 0.05. (Table 3). NUMBER OF PATIENTS Radiology Research and Practice 3 Table 2: Anterior circulation variant percentage distribution. ANTERIOR CW FREQUENCY (IN BOTH MALE AND FEMALES) FREQUENCY IN MALES FREQUENCY IN FEMALES TYPEA 78.7% (n=74) 69.8% (n=37) 90.2% (n=37) TYPE B 0% (n=0) TYPE C 1.1% (n=1) TYPE D 4.3% (n=4) TYPE E 0% (n=0) TYPE F 0% (n=0) TYPE G 4.3% (n=4) TYPE H 11.7% (n=11) TYPE I 0% (n=0) TYPE J 0% (n=0) Figure 2: Axial cerebral CTA MIP image showing a complete CW Figure 3: Axial MIP image showing combined type A anterior configuration. circulation variant and type E posterior circulation variant. Table 3: Proportion of posterior circulation variants. 7. Complete Posterior Circulation POSTERIOR CW FREQUENCY Variants (TYPES A-C) TYPE A 27.7% (26) A complete posterior CW configuration was seen in 39.4% TYPE B 4.3% (4) (39.6% vs. 39% in males and females, respectively, p=0.953). TYPE C 7.4% (7) TYPE D 4.3% (4) TYPE E 41.5% (39) 7.1. Adult Congfi uration of the Posterior Cerebral Arteries. There was a signicfi antly higher proportion of adult PCA TYPE F 2.1% (2) configuration in females than males (95%vs 81% p=0.044). TYPE G 7.4% (7) TYPE H 0% (0) TYPE I 0% (0) 8. Fetal PCA TYPE J 5.3% (5) Fetal PCA (Figure 4) was seen in 25.5% (28.3% vs. 22.0% in males and females, respectively, p=0.484). 6. Complete Anterior Circulation 9. Presence of Aneurysms and Location Variants (TYPES A-F) Aneurysms were seen in 24.5% of the patients referred for A complete anterior CW configuration was seen in 84%. The cerebral CTA (Table 4). proportion of this configuration was significantly higher in Figure 5 demonstrates a saccular aneurysm involving the females than males (92.7% vs. 77.4%, p=0.044). ACoA. 4 Radiology Research and Practice Figure 5: 3D cerebral CTA showing a saccular aneurysm at the ACoA. Figure 4: Axial cerebral CTA image showing bilateral fetal PCA with right P1 segment aplasia. Table 4: Distribution of intracranial aneurysms. Location of aneurysms ACOA 10 43.60% MCA 5 21.70% ICA 5 21.70% Other vessels than 3 13.00% Figure 6: 3D cerebral CTA image showing an AVM with feeding artery arising from the left MCA. 10. Association of CW Configuration and Aneurysms There was no association between CW configuration and Variations in the CW configuration have been associated presence of aneurysms as shown in Table 5. with cerebrovascular diseases [20, 21]. Various methods have been proposed for classification of 11. Presence of Cerebral variant anatomy of CW. The classification of CW configura- tion in this study is based on the Chen et al. classification Arteriovenous Malformations which classified anterior and posterior variants into 10 groups AVMs were seen in 8 (8.5%) of patients undergoing cerebral (A-J) [18, 19]. CTA (Figure 6). No association was found between CW The proportion of patients with complete CW configura- configuration and presence of AVM (P=0.987). tion was 37.2% (n=35). This was slightly higher in males than Fenestrations, duplications, azygous ACA, and persistent females: 37.7% vs. 36.6%. The findings in the current study TA were not observed in this study. are consistent with previous studies which have demonstrated a prevalence of between 12.24%-60% [19, 22]. An MRA- TOF study by Chuanya Qiu et al. on 2246 healthy Chinese 12. Discussion male population showed a lower prevalence of complete CW Previous anatomic, CTA, and MRA studies have demon- at 12.24% [4]. In contrast, an Egyptian MRA-TOF study strated significant variations in the configuration of the CW by Mohammed Abdelatif et al. on 180 patients with no in various population groups. manifestations of cerebrovascular disease showed a higher The purpose of this study was to determine the propor- prevalence of complete CW in 46.7% [23]. In our study, patients with cerebrovascular diseases referred for cerebral tion of variant anatomy of the circle of Willis (CW) and associated anomalies in patients with suspected cerebrovas- CTA were included unlike the above two MRA-TOF studies cular disease referred for cerebral CTA in 2 tertiary Kenyan which were conducted on patients with no manifestations hospitals. No similar studies on the CW configuration have of cerebrovascular disease. The findings in the current study been done in Kenya. could thus be attributed to the difference in the study Radiology Research and Practice 5 Table 5: Presence and number of aneurysms in complete and incomplete CW. Circle of WILLS anatomy Total Pvalue Characteristics Incomplete Complete Presence of Aneurysm No 71(75.5%) 43(72.9%) 28(80.0%) 0.438 Yes 23(24.5%) 16(27.1%) 7(20.0%) Number of Aneurysms 1 Aneurysm 18(78.3%) 12(75.0%) 6(85.7%) 0.567 More than 1 Aneurysm 5(21.7%) 4(25.0%) 1(14.3%) population, technique used, racial differences, and the lower was seen in 24.5%. Unilateral fetal PCA was more common than bilateral fetal PCA. 12.8% were right sided, 10.6% left sample size used in this study. An incomplete CW configuration was seen in 62.8% of sided, and 5.6% bilateral fetal PCA. patients, 62.3% in males versus 63.4% in females. Previous These findings are similar to a publication by Dimmick SJ studies have demonstrated a correlation between an incom- Faulder et al. which show a prevalence of 15%-32% for fetal plete CW and stroke severity and prognosis [10, 24]. PCA with bilateral fPCA at 8%, right sided at 10%, and left According to the Chen et al., classification type A-F sided fPCA at 10% [13]. Fetal PCA has been found to increase anterior variants are considered to be complete [18]. In our the extent and severity of anterior circulation stroke as well study, a complete anterior CW was seen in 84% (n=79). A as aneurysm formation [11, 31]. complete anterior CW was significantly higher in female than In the current study, aneurysms were seen in 24.5% male patients (92.7% vs. 77.4%, p=0.04). The prevalence of (n=23) of patients referred for cerebral CTA. 69.6% of the complete anterior CW in this study was higher than an MRA- aneurysms were located in the anterior CW while 4.3% were located in the posterior CW. 78.3% of patients had one TOF study by Sherif Mohamed Zaki et al. on 100 patents with no evidence of cerebrovascular disease which showed aneurysm while21.7% had morethan 1 aneurysm. a prevalence of 66% [25]. The finding in our study was also 26.1% (n=6) were located in other vessels other than higher than an MRA-TOF study by Shartri J et al. on 513 the CW. The prevalence of aneurysms in this study is lower adults without cerebrovascular disease which demonstrated a than that in an earlier Kenyan study by Chepsiror et al. complete anterior CW in 64.3% [26]. The higher prevalence based on conventional angiography which showed a higher of a complete anterior CW in our study could be due to higher prevalence of aneurysms at 40.9% and anterior circulation spatial resolution of CTA as compared to MRA, sample size aneurysms at 95.2% [32]. The study by Chepsiror et al. differences, and racial differences. was done on 88 patients with suspected cerebrovascular The commonest anterior circulation variant was type A disease who were referred for conventional angiography in variant accounting for 78.7% (n=74). This configuration was the two tertiary hospitals in Kenya. The difference in general seen in 69.8% (n=37) and 90.2% (n=37) of males and females, prevalence of aneurysms in the two studies could be due respectively. This finding is similar to studies done by Naveen to the higher sensitivity of conventional angiography for SR et al. and Dr. Arjun Bhaddur et al. which showed type A aneurysm detection. variant being the most common anterior circulation variant In the current study, ACoA aneurysms were the com- [27, 28]. monest at 43.6% (n=10). Type E posterior variant has been associated with 21.7% were located in the MCA, 21.7% were located in increased risk of ischaemic stroke [8]. This variant is of the ICA, and 13% were seen in other vessels than the CW. importance to surgeons and neurologists in the evaluation These findings are similar to a multimodality study on size of patients with intracranial tumors, traumatic injuries, and andlocation ofrupturedintracranial aneurysms by Young cardiovascular complications [29]. Gyun et al. which showed that a majority of aneurysms were In our study, type E posterior circulation variant was located in the ACoA [33]. These study findings are, however, the commonest posterior circulation variant accounting for in contrast to a conventional angiographic study on pattern 41.5%. This study finding is similar to findings on an MRA- of cerebrovascular disease in Kenyatta and Nairobi hospitals TOF study by Reddy Ravikanth et al. which demonstrated a doneby Chepsiror etal. which showed 30.6% atICA-PCoA, predominance of type E posterior circulation at 53% [30]. ACoA 22.2%, and MCA bifurcation 13% [32]. A cerebral CTA study done by Zhang Ning Jin et al. AVMs were seen in 8.5% (n=8) in the current study. on Chinese population with family history of stroke showed 62.5% (n=5) had incomplete CW while 37.5% (n=3) had a dominance of type E posterior variant with a prevalence of complete CW configuration. 52.3% [4], which is higher than the current study. The slight These study findings are similar to an earlier Kenyan conventional angiographic study by Chepsiror et al. which difference in prevalence of type E posterior variant could be due to racial and sample size differences. showed a prevalence of 8% [32]. In the current study, fetal PCA was seen in 30.9% (n=29). Association between duplication and fenestration of Complete PCA was demonstrated in 6.4% while partial PCA intracranial arteries with aneurysmal formation has been 6 Radiology Research and Practice documented in previous studies [13, 34]. Fenestration and Data Availability duplication of CW were not observed in our study. Previous Original data can be accessed upon request. publication by Dimmick SJ Faulder et al. has shown a low prevalence for duplications and fenestrations in angiographic studies of 0.058% [13]. A similarly low prevalence of anterior Disclosure circulation fenestration at 0.48% was demonstrated in a study This manuscript was submitted to the University of Nairobi as by Roger M et al. on 411 patients undergoing cerebral CTA [35]. part of fulfillment for master’s degree in diagnostic radiology. In the study by Roger M et al., patients with intracra- nial pathology such as subarachnoid hemorrhage, stroke, Conflicts of Interest tumor, and aneurysms were excluded from the study. In a previous Kenyan cadaveric study by Hassan Said et al. on The authors declare that there are no conflicts of interest 36 adult brains, fenestration and duplication of ACoA were regarding the publication of this manuscript. seen in 26% and 13%, respectively [36]. Another study by Dhanalakshmi V et al. on 50 adult cadaveric brains showed References a relatively lower prevalence of duplications and fenestration of the ACoA at 8% and 4%, respectively [37]. The absence [1] S. Kathuria, L. Gregg, J. 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