Abstract
BACKGROUND AND PURPOSE: Incidental findings on brain MRI and variations of the circle of Willis (CoW) are relatively common among the general population. Ethnic differences have been described before, but few studies have explored the prevalence of incidental intracranial cerebrovascular findings and CoW variants in the setting of a single multiethnic cohort. The purpose of this investigation was to describe both incidental cerebrovascular findings and the morphology of the CoW on high-resolution 3T TOF-MRA in a UK tri-ethnic population-based cohort and to present updated prevalence estimates and morphologic reference values.
MATERIALS AND METHODS: We studied participants from the UK Southall and Brent REvisited study who underwent 3T brain MRI between 2014 and 2018. TOF-MRA images were assessed for the presence of incidental cerebrovascular findings and used to determine CoW anatomy.
RESULTS: Seven hundred fifty participants (mean age, 71.28 [SD, 6.46] years; range, 46–90 years; 337 women), 322 White Europeans, 253 South Asians, and 175 African Caribbeans were included. Incidental cerebrovascular findings were observed in 84 subjects (11.2%, 95% CI, 9.0%–13.7%; 36 women; 42.86%, 95% CI, 32.11%–54.12%), with cerebral aneurysms being the most frequent followed by intracranial arterial stenoses with the highest prevalence among South Asians compared with White European (OR: 2.72; 95% CI, 1.22–6.08; P = .015) and African Caribbean subjects (OR: 2.79; 95% CI, 1.00–7.82; P = .051). Other findings included arteriovenous malformations and infundibula. The CoW was found to be more often complete in women than in men (25.22% compared with 18.41%, P = .024) and in African Caribbean (34.86%) compared with White European (19.19%) and South Asian (14.23%) subjects (P < .001 each).
CONCLUSIONS: Intracranial arterial stenoses were independently associated with ethnicity after adjusting for vascular risk factors, having the highest prevalence among South Asians. The prevalence of aneurysms was higher than that in previous population-based studies. We observed anatomic differences in the CoW configuration among women, men, and ethnicities.
ABBREVIATIONS:
- ACA
- anterior cerebral artery
- AcomA
- anterior comunicating artery
- CoW
- circle of Willis
- CVM
- cerebral vascular malformations
- ICAS
- intracranial arterial stenoses
- PCA
- posterior cerebral artery
- PcomA
- posterior communicating artery
SUMMARY
PREVIOUS LITERATURE:
Detection of incidental findings on brain MRI and MRA examinations is not uncommon, and ethnic differences in cerebrovascular diseases have been described previously. However large population-based studies exploring the prevalence of incidental cerebrovascular findings in multiethnic cohorts remain scarce. Previous investigations have also suggested some differences in the CoW anatomy between sex and ethnicity, with partially contradictory and ultimately inconclusive findings. The aim of this investigation was a comprehensive assessment of the prevalence of incidental cerebrovascular findings and morphologic variants of the CoW in a healthy elderly tri-ethnic population using 3T TOF-MRA.
KEY FINDINGS:
South Asian ethnicity has been shown to be an independent predictor of incidental intracranial arterial stenoses on 3T TOF-MRA after adjusting for vascular risk factors. Differences in CoW anatomy were observed between sex and ethnic groups but showed no significant associations with the incidence or spatial distribution of cerebrovascular findings.
KNOWLEDGE ADVANCEMENT:
This cohort study provides an update on the prevalence of incidental cerebrovascular findings and variants of the CoW on 3T TOF-MRA in 3 different ethnic Sgroups. The results contribute to our understanding of both sex and ethnic differences in cerebrovascular diseases and have the potential to improve risk factor profiling, screening, and therapeutic pathways.
Advances in MR and CT angiography allow noninvasive acquisition of high-resolution images of the intracranial vessels.1 More widespread use of these techniques resulted in increasing detection of incidental vascular abnormalities such as intracranial arterial stenoses (ICAS), aneurysms, or cerebral vascular malformations (CVM). Furthermore, these techniques allow noninvasive visualization of the circle of Willis (CoW) and its anatomic variants, which have a bearing on the outcome in steno-occlusive disease of the neck vessels and stroke. The prevalence of incidental brain imaging findings varies, depending on the population studied, which may differ in age or ethnic origin, as well as on the specific imaging techniques used.2,3 While ethnic differences in the pathogenesis of cerebrovascular diseases have been described before, large population-based studies exploring the prevalence of incidental intracranial cerebrovascular findings in the setting of a single multiethnic cohort remain scarce.
Anatomic variants of the CoW have been linked to the pathogenesis of several cerebrovascular diseases, including the risk of stroke or aneurysm formation.4⇓⇓-7 For example, hypoplasia or agenesis of the A1 segment of the anterior cerebral artery (ACA) has been implicated as a risk factor for ischemic stroke and aneurysms of the anterior communicating artery (AcomA) complex.7,8 In the presence of a fetal-type posterior cerebral artery (PCA), most of the ipsilateral PCA territory is supplied by the anterior circulation, which is important for the correct interpretation of arterial territories involved in the setting of acute stroke, as are other variants of the CoW.9 Several investigators have postulated that the morphologic variations of the CoW differ among ethnic groups, as well as between sexes, partially explaining the varying prevalence of cerebrovascular disease in different populations. With contradictory reports on the prevalence of CoW variations, further clarification of this topic is warranted. Previous efforts have been complicated by methodologic challenges, particularly concerning the noncomparability of in vivo and postmortem studies as well as the heterogeneity of the respective study populations.10⇓⇓-13
With this large population-based study of an elderly tri-ethnic population using standardized high-resolution 3T TOF-MRA, we aimed to assess the prevalence of incidental cerebrovascular findings and morphologic variants of the CoW, establishing a robust reference in an older multiethnic population.
MATERIALS AND METHODS
Study Setting
The sociodemographic and neuroradiologic imaging data used were obtained from the Southall and Brent REvisited (SABRE) study, follow-up visit 3, a prospective UK population-based cohort study investigating cardiovascular disease among people of self-identified European, South Asian, and African Caribbean origin. The cohort profile update, objectives, and study design have been reported in detail previously.14 Ethics committee approval was obtained from the London Fulham Research Ethics Committee under reference No. 14/LO/108.
Image Acquisition
All MR scans were acquired in a single clinical center, the University College London Hospitals NHS Foundation Trust, using a 3T whole-body MR system (Achieva; Philips Healthcare) fitted with an 8-channel sensitivity-encoding head phased array receiver coil (SENSE Head 8, Philips Healthcare). The MRI scanning protocol was uniform for all participants and consisted of 10 different high-resolution sequences (T2 fast-field echo; T1 3D turbo field echo (TFE); FLAIR 3D inversion recovery TSE; DTI EPI; TOF-MRA; pseudocontinuous arterial spin-labeling EPI; T2 3D TSE; B0 3D fast-field echo) with an overall scanning time of 33 minutes 30 seconds.
For the TOF-MRA, a 3D gradient-echo sequence was used to acquire 140 axial slices over a 200 × 200 × 70 mm FOV (RL × AP × FH). The scan acquired data in 4 chunks, and to reduce venetian blind artifacts, a linearly varying flip angle over each chunk (“TONE”) was used with a starting flip angle of 17°. A saturation slab was positioned superiorly to suppress venous blood. The acquired voxel sizes were 0.70 × 0.40 × 0.50 mm, reconstructed to a 560 × 560 in-plane matrix, with reconstructed voxel sizes of 0.36 × 0.36 × 0.50 mm. The TR/TE values were 25/3.5 ms with a nominal flip angle of 20°; radiofrequency spoiling was used for T1-weighted contrast, and the sequence duration was 6 minutes 0 seconds.
Image Analysis
The TOF-MRA sequences were assessed independently by a neuroradiologist and a radiologist (H.R.J. with 28 years and R.R. with 5 years of experience), with differences resolved by consensus. H.R.J. assessed the MRI studies for both vascular and nonvascular incidental findings using a structured report. Actionable incidental findings were defined in the study protocol and were communicated to relevant clinical specialists or the general practitioners. R.R. subsequently performed an independent reading for incidental cerebrovascular imaging findings and the characterization of the CoW.
Clinically significant ICAS was defined as a 50%–99% focal narrowing of the major intracranial arteries as in previous studies.15 Saccular aneurysms were distinguished from infundibula by the clear visualization of a vessel originating from the apex of an outpouching.
The CoW was assessed using the TOF-MRA images, using the source images as well as the respective 3D MIP reconstructions according to the reference classification established by Krabbe-Hartkamp et al,4 while rare morphologic variants were categorized on the basis of the work of Dimmick and Faulder.16
Data Analysis
All findings are presented as counts and percentages when appropriate. Confidence intervals, with reporting restricted to the main outcomes of the study, have been estimated at the 95% level (bootstrap 95% CI, 1000 iterations). The prevalence of the findings was compared across women and men as well as ethnicity using the Pearson χ2 test. ORs were obtained from logistic regression models, adjusted for age and sex as well as vascular risk factors, diabetes, hypertension, and low-density lipoprotein hyperlipidemia when appropriate (Online Supplemental Data). κ values were calculated to assess interrater reliability. Statistical software (Stata 15.1; Stata Corp; and R; Version 4.1.0; http://www.r-project.org) was used to perform all analyses.
RESULTS
Population Demographics
Basic demographic and lifestyle characteristics are shown in the Online Supplemental Data. Inclusion and exclusion criteria are detailed in Fig 1.
Study inclusion and exclusion flow chart.
Incidental Cerebrovascular Findings
Interobserver Agreement.
Interobserver agreement for incidental cerebrovascular findings was overall very high (κ = 0.987). With a total of 84/750 subjects with incidental findings, there were 3 cases of disagreement between the raters: One small saccular aneurysm was missed, the degree of a <50% stenosis of the terminal ICA was overestimated, and 1 infundibulum was misinterpreted as an aneurysm. These discrepancies were resolved by consensus.
Prevalence and Spatial Distribution.
Of the 750 study volunteers, incidental cerebrovascular findings were found in a total of 84 subjects (11.20%; 95% CI, 9.03%–13.68%), of whom 36 were women (42.86%; 95% CI, 32.11%–54.12%) and 48 men (57.14%; 95% CI, 45.88%–67.89%). Incidental cerebrovascular findings were observed in 38/322 White Europeans (11.80%; 95% CI, 8.49%–15.84%), 30/253 South Asians (11.86%; 95% CI, 8.15%–16.49%), and among 16/175 study participants of African Caribbean descent (9.14%; 95% CI, 5.32%–14.42%). In 11 subjects (1.47%; 95% CI, 0.8%–2.6%), a second incidental finding of the same type, was observed, resulting in an overall prevalence of approximately 127 per 1000 cases.
Overall, cerebral aneurysms were the most common incidental finding, with a prevalence of 37/750 subjects (4.93%, 95% CI, 3.50%–6.73%) and a mean maximum diameter of 2.87 [SD, 1.36] mm; range, 1.00–6.60 mm. Primary cerebral aneurysms were most commonly located in the ICA (n = 20, 54.05%; 95% CI, 36.92%–70.51%), with 9 (45.00%) in the left and 11 in the right ICA (55.00%). The second most common site of incidentally discovered cerebral aneurysms was the MCA, with a total of 7 cases (18.92%; 95% CI, 7.96%–35.16%), of which 4 were in the left (57.14%) and 3 in the right (42.86%) hemisphere, followed by the ACA in which a total of 4 aneurysms (10.81%, 95% CI, 3.03%–25.42%) were identified (1 left [25.00%], 3 right [75%]). For the basilar artery and AcomA, 2 aneurysms were identified in each vessel (5.41%; 95% CI, 0.66%–18.19%), and 1 aneurysm was observed in both the left PCA and left posterior communicating artery (PcomA; 2.70%, 95% CI, 0.01%–14%). Two subjects had 2 aneurysms, (basilar artery and left MCA; left ICA and right ACA). A detailed summary of the respective aneurysm sites is shown in Fig 3. No evidence of relevant differences between White Europeans and South Asians (OR: 0.84; 95% CI, 0.38–1.90; P = .682) or African Caribbeans (OR: 1.28; 95% CI, 0.55–2.96; P = .569), women and men (OR: 0.69; 95% CI, 0.34–1.40; P = .309), has been found.
The second most common incidental findings were ICAS of presumed arteriosclerotic origin, with a prevalence of 35/750 participants (4.67%; 95% CI, 3.27%–6.43%), and in 9 of these subjects (25.74%; 95% CI, 12.49%–43.26%), a second stenotic lesion was identified. In 1 subject (0.13%; 95% CI, 0.00%–0.74%), a White European woman (78 years of age), a complete intracranial arterial occlusion was also observed. Within the individual ethnic groups, ICAS was observed among 10/322 subjects of White European origin (3.10%; 95% CI, 1.50%–5.64%; 1 woman), 20/253 South Asian subjects (7.90%; 95% CI, 4.90%–11.94%; 7 women), and 5/180 African Caribbean participants (2.86%; 95% CI, 0.93%–6.54%; 4 women), showing a higher prevalence of ICAS among South Asians compared with White European (OR: 2.72; 95% CI, 1.22–6.08; P = .015) and African Caribbean subjects (OR: 2.79; 95% CI, 1.00–7.82; P = .051; Fig 2). There was no evidence of differences between women and men (OR: 1.33; 95% CI, 0.61–2.87; P = .475).
Barplots showing the frequency and 95% CI of the incidental cerebrovascular imaging findings on 3T TOF-MRA by ethnicity.
Schematic illustrations of the major intracranial arterial structures detailing the spatial distribution and frequency of identified incidental intracranial aneurysms (A) and stenotic lesions (B) by ethnicity.
In the subjects for whom an ICAS was found, the lesions were observed in the ICA in 24/35 cases (68.57%; 95% CI, 50.71%–83.15%), of which 7 (29.17%) were found in the left and 17 (70.83%) in the right ICA. In the MCA, stenotic lesions were found in a total of 5 subjects (14.29%; 95% CI, 4.81%–30.26%), with 2 (40.00%) lesions located in the left and 3 (60.00%) in the right cerebral hemisphere. A further 4 stenotic lesions (11.43%; 95% CI, 3.20%–26.74%) were found in the PCA (1 left [25.00%], 3 right [75.00%]), while 1 stenosis was found in both the basilar artery and the left vertebral artery (2.86%; 95% CI, 0.07%–14.92%, respectively).
Intracranial infundibula were found in 4/322 White European subjects (1.24%; 95% CI, 0.33%–3.15%), 2/253 South Asians (0.79%; 95% CI, 0.00%–2.83%), and 3/175 African Caribbean participants (1.71%; 95% CI, 0.35%–4.93%), and they were most frequently observed at the origin of the PcomA (3/9 cases, 33.33%). Other locations were the superior cerebellar artery and PCA (2 each, 22.11%), the MCA and ophthalmic artery, with 1 infundibular outpouching identified in each of these sites (11.11%). No evidence of differences between White European and South Asian (OR: 0.66; 95% CI, 0.12–3.72; P = .636), African Caribbean (OR: 1.31; 95% CI, 0.27–6.43; P = .740), or women and men (OR: 0.61; 95% CI, 0.15–2.50; P = .489) has been found.
CVMs were found in 3/750 subjects (0.40%; 95% CI, 0.08%–1.16%). Of these, 2 subjects (0.26%; 95% CI, 0.03%–0.96%), both White European men, 68 and 76 years of age, had a CVM and 1 (0.13%; 95% CI, 0.00%–0.74%), an African Caribbean woman (72 years of age), had a dural fistula. The CVMs identified were located in the superior vermis and the left cerebellar hemisphere, respectively, and the dural fistula was located in the right transverse sinus.
CoW Anatomy
The observed CoW variants and their overall frequency are detailed in Fig 4 and the Online Supplemental Data.
Illustration of the observed anatomic variants of the anterior (A) and posterior (B) CoW with numbers and overall frequency. The upper panel shows functionally complete and lower panel, functionally incomplete variants, respectively. c-SCA indicates the PCA P1 segment arising from the ipsilateral superior cerebellar artery (SCA); PDUP, ipsilateral duplication of the PCA; Azg, azygos ACA; BiHemACA, bihemispheric ACA; ACAH, unilateral ACA hypoplasia; c3, duplication of the median artery of the corpus callosum; h3, unilateral ACA trifurcation. The asterisk indicates normal PCA anatomy; †, unilateral fetal-type PCA; ‡, bilateral fetal-type PCA.
The CoW, as a whole, was significantly more often found to be complete in women than in men (25.22% compared with 18.41%, P = .024), while it was also most often complete in African Caribbean (34.86%) compared with White European (19.19%) and South Asian (14.23%) subjects (P < .001 each; Fig 5).
Barplots showing the frequency and 95% CI of an overall complete CoW and a complete anterior and complete posterior CoW by ethnicity. Group differences have been estimated using the Pearson χ2 test.
Regarding the completeness of the anterior CoW in the overall cohort, there was no evidence of differences between women and men (P = .488) or by ethnicity (Fig 4). However, regarding women only, a complete anterior circle was more common among White European compared with South Asian and African Caribbean women (70.09% compared with 52.78% and 57.14%; P = .008 and P = .042). In the posterior circulation, a complete CoW was found significantly more often in men than in women (71.91% compared with 61.13%, P = .002). The frequency of a complete posterior CoW was also significantly higher in the African Caribbean population than in either the White European or South Asian populations (P < .001 each; Fig 4), while White Europeans were found to have a complete posterior circle significantly more often than South Asians (P = .003, Fig 4).
Regarding ethnic variations for each sex separately, similar results regarding a complete posterior CoW were found for men (31.22% in White European compared with 15.17% in South Asian and 47.62% in African Caribbean men, P = .001 and P = .017; [South Asian compared with African Caribbean, men P < .001]). For women, a complete posterior CoW was also significantly more frequently observed in African Caribbean (52.68%) compared with White European (34.89%) and South Asian (29.63%) women (P = .005 and P = .001), while the difference between White European and South Asian women was much less pronounced (P = .464).
While there was no difference between women and men overall regarding the fetal-type configuration of the PCA (P = .363), a bilateral fetal PCA was found significantly more often in the African Caribbean population (17.14%) than in the White European (11.49%) or South Asian populations (7.91%; P = .008 and P < .001). For women, no differences were found between the ethnic populations regarding the prevalence of either anatomic variant of the posterior CoW (P = .932). However, a bilateral fetal PCA was significantly more common among African Caribbean men (22.22%) than among either White European (10.24%) or South Asian men (4.83%; P = .014 and P < .001), while a bilateral normal PCA anatomy was more prevalent in South Asian (74.48%) compared with African Caribbean men (58.73%; P = .024). Furthermore, there was no evidence for an association between the occurrence or location of an aneurysm and the anterior, posterior, or overall anatomical variation of the CoW.
DISCUSSION
With a mean age of 71.28 (SD, 6.46) years (range, 46–90 years), the volunteers in this study represent an elderly general population sample, comparable with the MRA-based analysis by Krabbe-Hartkamp et al4 or the Insight 46 (https://www.ucl.ac.uk/drc/research-clinical-trials/insight-46) birth cohort and are slightly older than other population-based cohorts, such as the Rotterdam Scan Study.2,3,17
This cohort represents a uniquely diverse sample of 3 different ethnic populations, which is yet unmatched in the existing literature in the context of using high-resolution TOF-MRA to investigate cerebrovascular imaging findings. White European subjects (42.93%) were relatively overrepresented compared with South Asian (33.73%) or African Caribbean subjects (23.33%).
Cerebral aneurysms were the most common incidental finding with no differences in prevalence among the 3 ethnic groups. The observed overall prevalence of 4.93% and particularly the prevalence among White Europeans (5.28%) are higher than that reported in other studies.3,18
Studies exploring the prevalence of intracranial aneurysms in African populations or African diaspora communities are rare: Initial reports dealing with the treatment of ruptured intracranial aneurysms appeared to show a lower incidence of intracranial aneurysms compared with Western populations.19 More recent reports demonstrated, however, that intracranial aneurysms are not uncommon among African populations, a likely explanation being the wider availability of noninvasive neuroimaging.19⇓⇓⇓-23 This is, to our knowledge, the first study using 3T TOF-MRA to report the prevalence of incidental unruptured intracranial aneurysms and adjusting the OR for cerebrovascular risk factors in an elderly African Caribbean subgroup (5.71%), thereby establishing an important reference for future investigations.
One might conjecture that the higher prevalence of intracranial aneurysms in this study could be related to the relatively advanced age of the study population. A comprehensive meta-analysis by Vlak et al24 found, however, no significant relationship between age and unruptured intracranial aneurysms, except for a lower prevalence in subjects younger than 30 years of age.25,26 A more likely explanation for the higher prevalence of aneurysms in this study is the use of high-resolution 3T TOF-MRA. Whereas medium- and large-sized aneurysms can easily be detected on standard MRI sequences, small aneurysms may be visible only on 3T MRA imaging, which has a higher diagnostic yield for aneurysms.27⇓-29
The second most common incidental cerebrovascular finding was ICAS (4.67%). Only a few reports mention the prevalence and epidemiology of ICAS in the general population, accounting for additional vascular risk factors: Vernooij et al3 observed large-vessel stenosis in 9 patients (0.5%, 1.5T MRI) in an elderly Dutch cohort, while the US Atherosclerosis Risk in Communities Study found ICAS prevalent in 31% of the study population, (67–90 years of age; 3T MRA) and estimated the US prevalence of ICAS of >50% to be 8% for Whites and 12% for African-Americans 65–90 years of age.30
Ethnic disparities regarding the incidence and spatial distribution of arteriosclerotic cerebrovascular lesions were first reported in 1962.31 The significantly higher prevalence of ICAS of >50% in the South Asian population in our study, compared with both White and African Caribbean subjects, is not entirely unexpected, given the results from previous investigations.32⇓-34 In contrast to some previous reports, we did not observe a significant difference between African Caribbean and White European individuals, a finding in line with some earlier findings.31,33,35 The higher prevalence of ICAS among different ethnic groups has been explored in previous investigations, because it is a major cause of stroke in Asian and African populations, a fact that has been linked to genetic predisposition, morphologic characteristics of the cerebral arteries, and divergent risk factor profiles.34,36
Regarding the overall prevalence of the morphologic variants of the CoW, types a (39.33%) and g (26.13%) were most commonly observed in the anterior CoW, and types d (24.67%), e (22.13%), and a (19.33%) were the most common variants in the posterior compartment, results comparing well with the results of previous investigations using the same classification.4,37 The most frequently found combinations of the anterior and posterior CoW types are, hence, in accordance with the existing literature. Considering the anatomic variability of the CoW in its entirety, a unilaterally absent PcomA (posterior CoW type d) in combination with an anterior CoW type a was marginally more frequent (n = 82, 10.93%; 95% CI, 8.79%–13.39%) than type a, the hemodynamically “ideal” arterial anatomy in both the anterior and posterior divisions (n = 68, 9.07%; 95% CI, 7.11%–11.35%). The topographic pattern of the CoW is determined during embryogenesis, and it seems unlikely that any processes later in life can influence its configuration.6 In adulthood, an absent or nonfunctional PcomA, though asymptomatic under normal conditions, implies a less robust collateral circulation between the vertebrobasilar and internal carotid arterial systems.4,6,12 Hence, in cases of a unilateral missing or nonfunctional PcomA, a coincident AcomA, as the dominant contributor to interhemispheric blood flow, is hemodynamically advantageous and key to preventing low-flow or borderzone infarcts in ipsilateral ICA stenoses or occlusions.38⇓⇓-41
A study involving 1131 individuals with acute ischemic stroke and 662 controls showed a higher prevalence of anatomic variations in the CoW among patients with stroke compared with controls, with the most prevalent variants identified being hypoplastic A1 segments and a fetal-type PCA.5 Another study found a less favorable prognosis in patients with stroke with an incomplete CoW.42
In our study, significant differences in CoW anatomy were observed between women and men as well as among the different ethnic groups. These morphologic differences do not relate to a single vascular configuration only but were observed in the overall structure of the entire circle, in the anterior and posterior divisions separately and in relation to the configuration of the PCA. The present findings provide evidence of ethnic differences in the prevalence of an overall complete circle, because a complete CoW was more common in the African Caribbean compared with South Asian and White European populations overall.
Several factors may account for the high variability observed in the CoW, including developmental, partially transient, modifications or genetic patterns related to CoW variations, as suggested by recent evidence indicating a hereditary predisposition to incomplete variants of the PComA.11,43⇓-45 Clinically, these results could contribute to an understanding of both sex and ethnic differences in cerebrovascular diseases, including stroke subtypes, risk of aneurysm formation, and distribution and volume of white matter hyperintensities.46⇓-48
There are some potential limitations to the present study. Unenhanced TOF-MRA has some limitations in depicting turbulent or slow flow. The degree of ICAS may have potentially been overestimated due to intravoxel spin dephasing in turbulent flow, and the prevalence of absent and hypoplastic AcomAs and PcomAs may have been slightly overestimated due to nonvisualization of slow flow in these vessels.4 The effects of turbulent and slow flow were, however, mitigated by using an optimized high-resolution imaging protocol at 3T, substantially improving the SNR and allowing a more detailed visualization of smaller vessels secondary to prolonged T1 relaxation.49 Sensitivity for the detection of aneurysms with TOF-MRA at 3T has been shown to be very high compared with DSA as the criterion standard.50 Therefore, the chance of missing any potential small aneurysms is likely very low. We did not find a link between CoW anatomic variants and the observed incidental vascular pathologies; however, this could be attributed, at least partially, to the small number of specific incidental findings.
A further potential limitation is the advanced age of SABRE participants; therefore, no comments can be made on the incidence of arterial stenosis and aneurysms in younger age groups. Finally, because the main purpose of this investigation was to describe ethnic differences in the prevalence of incidental pathologic cerebrovascular imaging findings and configurations of the CoW, we did not perform an exhaustive data collection on further possible arterial variants, such as, for example, persistent carotid-vertebrobasilar anastomoses and abnormal origins of the ophthalmic or middle meningeal arteries.
CONCLUSIONS
In this large tri-ethnic population-based study, we explored ethnic differences in the prevalence of incidental cerebrovascular imaging and CoW morphology. Ethnic differences were found only for ICAS, with a higher prevalence in South Asians, The overall prevalence of aneurysms tended to be higher than in previous population-based studies, which is likely to reflect the use of 3T high-resolution TOF-MRA, allowing better detection of small aneurysms. We, furthermore, observed differences in CoW configurations among women and men and ethnicities.
Footnotes
Professor Nishi Chaturvedi received funding for this study by the British Heart Foundation (CS/13/1/30327).
Disclosure forms provided by the authors are available with the full text and PDF of this article at www.ajnr.org.
References
- Received April 21, 2024.
- Accepted after revision June 28, 2024.
- © 2024 by American Journal of Neuroradiology
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