Association between Anatomical Variations of the Circle of Willis and Covert Vascular Brain Injury in the General Population.

BACKGROUND AND PURPOSE: The circle of Willis (COW) is a circulatory anastomosis located at the base of the brain. Little is known about the association between covert vascular brain injury and COW configurations in the general population. We explored this relationship in a community-based Chinese sample. METHODS: A total of 1,055 patients (mean age, 54.8 ± 8.9 years; 36.0% men) without intracranial arterial stenosis were included in the analysis. Magnetic resonance imaging was performed to evaluate the presence of imaging markers of covert vascular brain injury, including white matter hyperintensities (WMHs), lacunes, cerebral microbleeds (CMBs), enlarged perivascular spaces, and brain atrophy. Magnetic resonance angiography was used to classify the COW configurations according to the completeness, symmetry, and presence of the fetal posterior cerebral artery (FTP). The association between vascular lesions and variations in COW was analyzed. RESULTS: Among the 1,055 patients, 104 (9.9%) had a complete COW. Completeness correlated with age (p = 0.001). Incomplete COW was positively associated with WMH severity (OR = 2.071; 95% CI, 1.004-4.270) and CMB presence (OR = 1.542; 95% CI, 1.012-2.348), independent of age and sex. The presence of FTP was associated with lacunes (OR = 1.878; 95% CI, 1.069-3.298), more severe WMHs (OR = 1.739; 95% CI, 1.064-2.842), and less severe enlarged perivascular spaces (OR = 0.562; 95% CI, 0.346-0.915). CONCLUSIONS: COW configuration was significantly related to various covert vascular brain injuries.

Age-related changes in the completeness of the circle of Willis in children.

PURPOSE: The circle of Willis is a circulatory anastomosis that supplies blood to the brain. If any of the bridging segments are hypoplastic or absent, the capacity for collateral flow in the setting of large vessel occlusion may be decreased. Outside of the neonatal period, the prevalence of a complete circle of Willis (CoW) in the pediatric population has not been well described. Our objectives include determining the prevalence of a complete CoW in children and identifying if there is an age-related "loss" of arterial segments. METHODS: Following IRB approval, angiograms of the CoW performed on a 3-T MR platform from 2016 to 2020 on patients 21 years or younger were retrospectively reviewed. Any patient with underlying arterial pathology that may affect the CoW was excluded. Patient age and gender at the time of imaging were obtained. RESULTS: In total, 592 pediatric CoW were assessed. Frequencies of completeness were calculated in two different fashions: scenario 1 where a CoW was characterized as complete even if it contained hypoplastic vessels (88.8%), and scenario 2 where it was characterized as complete after excluding hypoplastic vessels (44.0%). In both scenarios, our data showed that older age was more associated with an incomplete CoW (p < 0.0001). In addition, we found a higher percentage of males with an incomplete CoW compared with females (p < 0.0001). CONCLUSIONS: The presence of a complete CoW is greater in our pediatric population than what has been reported in adults. The prevalence of an incomplete circle of Willis also increases significantly with age.

Association between symptomatic intracranial atherosclerotic disease and the integrity of the circle of Willis.

The relationship between the severity of intracranial atherosclerotic disease and the circle of Willis integrity is unclear. In this brief report, we investigate the associations between symptomatic intracranial atherosclerotic disease and the integrity of the circle of Willis. Patients with symptomatic intracranial atherosclerosis were enrolled and underwent intracranial artery magnetic resonance vessel wall imaging and time-of-flight angiography. The presence or absence of an intracranial atherosclerotic plaque and its maximum wall thickness and stenosis were evaluated. The presence or absence of the A1 segment of the bilateral anterior cerebral arteries (from the internal carotid artery to the anterior communicating artery segment is called anterior cerebral artery A1 segment), and anterior communicating artery, the P1 segment of the bilateral posterior cerebral arteries (The P1 segment of the posterior cerebral artery is a horizontally outward segment), and bilateral posterior communicating arteries were determined. The associations of the intracranial plaque features with the integrity of the circle of Willis were analyzed. Of the 110 recruited subjects (57.2 ± 11.1 years; 65% males), 51 had intracranial plaques, and 44 had stenosis. In patients with bilateral A1 and P1 segments (n = 85), intracranial stenosis was more severe in patients with an anterior communicating artery than those without an anterior communicating artery (19.7% ± 21.7% vs. 1.4% ± 3.3%, p = 0.046). In patients with bilateral A1 and P1 segments and an anterior communicating artery (n = 79), intracranial stenosis was more severe in patients with posterior communicating arteries than those without posterior communicating arteries (27.9% ± 23.7% vs. 13.5% ± 17.9%, p = 0.007). The odds ratio of intracranial stenosis was 1.214 (95% confidence interval (CI), 1.054-1.398; p = 0.007) in discriminating for the presence of posterior communicating arteries in patients with bilateral A1 and P1 segments and an anterior communicating artery after adjusting for confounding factors. The severity of intracranial atherosclerosis was independently associated with the presence of posterior communicating arteries in patients with a complete anterior part of the circle of Willis.

Investigation of Flow Changes in Intracranial Vascular Disease Models Constructed with MRA Images.

This study aimed to develop a magnetic resonance imaging (MRI)-compatible flow delivery system and individualized models of circle of Willis (CoW), which include 50% and 100% blockage in internal carotid artery (ICA50 and ICA100), and 100% blockage in vertebral artery (VA100). Images were obtained using 3D time-of-flight and phase-contrast magnetic resonance angiography (MRA) sequences, and changes in velocity and flow direction at CoW models were analyzed. For the ICA50 and VA100 models, the flow was similar to that of the normal model. For the ICA 50 model, it was found that 50% blockage did not affect cerebral blood flow. For the VA100 model, decreased flow in the posterior cerebral artery and a change to the flow direction in the posterior communicating artery were found. For the ICA100 model, particularly, decreased flow in the ipsilateral middle and anterior cerebral arteries and a change to the flow direction in the ipsilateral anterior cerebral artery of the CoW were found. These results demonstrated that the flow system with various CoW disease models tailored to individual characteristics could be used to predict stroke onset more quickly. For the ICA50 and VA100 models, the possibility of cerebral infarction was significantly lower. On the other hand, for the ICA100 model, there was a high possibility of decreased flow, which could lead to cerebral infarction.

Anterior Cerebral Artery Stroke: Role of Collateral Systems on Infarct Topography.

Background and Purpose: The circle of Willis (CoW) and leptomeningeal anastomoses play an important role in transforming infarct topography following middle cerebral artery occlusion. Their role in infarct topography following anterior cerebral artery occlusion is not well understood. The aim of this study was to evaluate the role of the CoW and leptomeningeal anastomoses in modifying regional variation in infarct topography following occlusion of the anterior cerebral artery and its branches. Methods: Perfusion and magnetic resonance imaging of patients with anterior cerebral artery stroke and evidence of vessel occlusion were segmented and manually registered to standard brain template for voxel-wise comparison. Next, a computer model of the cerebral arteries was formulated as network of nodes connected by cylindrical pipes. The experiments included occlusion of successive branches of the anterior cerebral artery while the configurations of the CoW were varied. Results: Forty-seven patients with a median age of 77.5 years (interquartile range, 68.0­84.5 years) were studied. The regions with the highest probabilities of infarction were the superior frontal gyrus (probability =0.26) and anterior cingulate gyrus (probability =0.24). The regions around the posterior cingulate gyrus (probability =0.08), paracentral lobule (probability =0.05), precuneus and superior parietal lobule (probability =0.03) had a low probability of infarction. Following occlusions distal to the anterior communicating artery, the computer model demonstrated an increase in flow (>30%) in neighboring cortical arteries with leptomeningeal anastomoses. Conclusions: Traditionally the CoW has been regarded as the primary collateral system. However, our computer model shows that the CoW is only helpful in redirecting flow following proximal vessel occlusions (pre-anterior communicating artery). More important are leptomeningeal anastomoses, which play an essential role in distal vessel occlusions, influencing motor outcome by modifying the posterolateral extent of infarct topography.

Ruptured Infundibular dilatation of the posterior communicating artery.

OBJECTIVE: An infundibulum of the posterior communicating artery (PcomA) or infundibular dilatation (ID) is considered to be a benign anatomical variant. However, some evidence suggests that ID is a pre-aneurysmal state. This case series presents cases of ruptured IDs and aneurysms originating from the IDs. METHODS: Between April 2002 and June 2020, 1337 patients were treated for aneurysmal subarachnoid hemorrhage (SAH). Among them, 7 patients with ruptured PcomA IDs were identified. Rupture IDs of the PcomA were categorized into 1) direct rupture of IDs, and 2) rupture of aneurysms originating from IDs. The clinical and radiographic factors were retrospectively reviewed. RESULTS: Two patients experienced direct rupture of IDs, while the other 5 patients presented with ruptured aneurysms originating from IDs. The 2 patients with direct rupture of IDs at presentation were relatively younger (< 50 years), while the other 5 patients with ruptured aneurysms originating from IDs were over 70 and had a history of aneurysmal SAH due to other intracranial aneurysms. Ruptured IDs were treated with microsurgery or endovascular treatment. There were no complications related to the procedure for securing ruptured IDs. Five (71.4%) patients showed favorable outcomes. One patient with initial Hunt and Hess grade 4 died due to initial brain damage with cerebral vasospasm and medical complications. CONCLUSIONS: ID of the PcomA rarely causes SAH with or without aneurysm formation. Thus, patients with IDs of the PcomA should be carefully followed up for a long period, especially those with a history of aneurysmal SAH.

Arterial collateral anatomy predicts the risk for intra-operative changes in somatosensory evoked potentials in patients undergoing carotid endarterectomy: a prospective cohort study.

BACKGROUND: During carotid endarterectomy (CEA), significant amplitude decrement of somatosensory evoked potentials (SEPs) is associated with post-operative neurological deficits. OBJECTIVE: To investigate the association between an incomplete circle of Willis and/or contralateral ICA occlusion and subsequent changes in intra-operatively monitored SEPs. METHODS: We performed a retrospective analysis of a single center, prospective cohort of consecutive patients undergoing CEA over a 42-month period after reviewing the collateral arterial anatomy on pre-operative radiological imaging. The primary endpoint was an intra-operative decline in SEPs > 50% compared to the baseline value during arterial cross-clamping. Univariate and multivariate logistic regression analyses were performed to investigate a potential association between contralateral ICA occlusion, incomplete circle of Willis, and subsequent alteration in SEPs. RESULTS: A total of 140 consecutive patients were included, of which 116 patients (82.9%) had symptomatic carotid stenosis of at least 50% according to the classification used in the North American Carotid Surgery Trial (NASCET) (Stroke 22:711-720, 1991). Six patients (4.3%) showed contralateral ICA occlusion, 22 patients (16%) a missing/hypoplastic anterior communicating artery (Acom) or A1 segment, and 79 patients (56%) a missing ipsilateral posterior communicating artery (Pcom) or P1 segment. ICA occlusion and missing segments of the anterior circulation (missing A1 and/or missing Acom) were associated with the primary endpoint (p = 0.003 and p = 0.022, respectively). CONCLUSION: Contralateral ICA occlusion and missing anterior collaterals of the circle of Willis increase the risk of intra-operative SEP changes during CEA. Pre-operative assessment of collateral arterial anatomy might help identifying patients with an increased intra-operative risk.

Clip-wrapping of ruptured blood blister-like aneurysms of the internal carotid artery.

To evaluate the safety and validity of microsurgical Gore-Tex clip-wrapping for ruptured blood blister-like aneurysms (BBAs) of the internal carotid artery (ICA). Single-surgeon series. Retrospective study. Data analyzed were patient age, sex, Hunt and Hess grade (H&H), Fisher grade, time from rupture to hospitalization, aneurysm size and location, collateral capacity of the circle of Willis, time from hospitalization to aneurysm repair, aneurysm obliteration, complications, and modified Rankin scale (mRS) at follow-up. Six patients (2 males, 4 females) with ICA BBAs underwent clip-wrapping between 2011 and 2016. Median age was 50.0 years (range 31.7-54.0). H&H was grade 1 or 2 in 5 patients and grade 4 in 1 patient. All aneurysms were small (≤ 0.3 cm), without relation to vessel bifurcations, and located anteromedially, anterolaterally, and superomedially on the ICA trunk. Right side was most frequent (66%). All aneurysms could be clip-wrapped without intraoperative ruptures and all parent arteries could be preserved in the acute phase. Clip-wrapping completely eliminated the BBAs in five patients, whereas one patient underwent additional stent-assisted coiling. There were no re-ruptures, delayed infarctions, or deaths postoperatively. After a median follow-up of 57 months (range 20-90), outcome was favorable (mRS score 0-2) in all patients without radiographic signs of recurrences. Using the Gore-Tex clip-wrapping technique for ruptured ICA BBAs, the aneurysm could be treated without intraoperative ruptures or parent artery sacrifice in the acute phase. The outcomes were similar to other SAH patients and on follow-up, there were no aneurysm recurrences, indicating a durable long-term outcome.

Clinical and morphological risk factors for the recurrence of anterior communicating artery aneurysms after clipping or coiling.

BACKGROUND: The aim of this study was to evaluate clinical and morphological factors associated with recurrence in anterior communicating artery (AcomA) aneurysms after clipping or coiling. METHODS: We retrospectively reviewed the clinical and radiologic features of consecutive 214 patients with AcomA aneurysms treated between January 2012 and December 2016 in a single tertiary institute. Univariate and multivariate analyses were performed to identify the relationship between clinical and morphological variables and recurrence. RESULTS: Of 214 patients, 166 were unruptured aneurysms and 109 were treated with coiling. Overall recurrence rate was 13% (28 out of 214 aneurysms) during mean 36.9 ± 18.4-month follow-up. Multivariate logistic regression analysis showed that size greater than 10 mm (OR = 5.651; 95% CI, 1.317-24.242; p = 0.020), smoking (OR = 3.474; 95% CI, 1.342-8.996; p = 0.010), coiling (OR = 2.98; 95% CI, 1.005-8.832; p = 0.049), and anterior direction of aneurysm (OR = 3.77; 95% CI, 1.12-12.66; p = 0.032) were significantly associated with recurrence of AcomA aneurysms after treatment. CONCLUSIONS: The results of this study demonstrated that coiling, large aneurysm, anterior direction, and smoking history may be independent risk factors for the recurrence of AcomA aneurysms. Therefore, careful follow-up should be needed especially in large AcomA aneurysms with anterior direction after coiling.

Atypical Endovascular Cells in SARS-CoV-2 Pneumonia.

The autopsy findings for 3 cases of SARS-(CoV-2) pneumonia-related deaths are reported with pulmonary histology and immunohistochemistry findings. In 2 cases (cases 1 and 2), the time interval from presentation to death was approximately 1 week, whereas for case 3, the time interval from presentation to death was hours. Case 1 and case 2 presented with shortness of breath, cough, and flu-like symptoms. The decedent from case 3 died shortly after presenting to a local emergency room with high fever, chest and abdominal pain, and shortness of breath. All 3 cases had 1 or more comorbidities. The postmortem interval for cases 1 and 2 was 2 weeks as they died at sea and were stored on board within the respective cruise ships' refrigeration units, whereas case 3 was examined within 24 hours of death. The autopsies were conducted at the Miami-Dade County Medical Examiners Department under routine infectious precautions. Salient clinical history and autopsy findings are summarized. Microscopic examination revealed pneumonia with associated atypical endovascular cells.

ASL perfusion features and type of circle of Willis as imaging markers for cerebral hyperperfusion after carotid revascularization: a preliminary study.

OBJECTIVES: Cerebral hyperperfusion (CH) could be a disastrous outcome causing complication after carotid revascularization if not managed properly and timely. The aim of this study was to investigate the association between preoperative arterial spin labelling (ASL) perfusion features and circle of Willis (CoW) pattern with CH. METHODS: Forty-eight consecutive carotid stenosis patients who underwent carotid endarterectomy (CEA) or carotid artery stenting (CAS) were enrolled. All patients had single post-labelling delay (PLD) ASL, territory-ASL, and 3-dimensional time-of-flight MR angiography (3D TOF MRA) within 2 weeks before surgery and within 3 days after surgery. Spatial coefficient of variation (CoV) of cerebral blood flow (CBF), whole brain, and territory perfusion volume ratio were calculated from ASL and territory-ASL. Postoperative CoW was classified into two groups based on patency of the first segment of the anterior cerebral arteries (A1) and anterior communicating artery (AcomA). ASL perfusion features, type of CoW, and clinical characteristics were analyzed between CH group and non-CH group to identify CH risk factors. RESULTS: Higher CoV (p = 0.005) of CBF, lower whole brain perfusion volume ratio (p = 0.012), missing any of A1 or AcomA in CoW (p = 0.002 for postoperative MRA and p = 0.004 for preoperative MRA), and large artery stroke history (p = 0.028) were significantly associated with higher risk of CH. Two cases with cerebral hyperperfusion syndrome (CHS) were also discussed, and their perfusion and angiographic features were shown. CONCLUSIONS: Single-PLD ASL and MRA might be useful and non-invasive imaging tools to identify patients with higher risk of CH after carotid revascularization. KEY POINTS: • Cerebral hyperperfusion is a critical complication after carotid endarterectomy or carotid artery stenting. • ASL and MRA can be used to identify patients at higher risk of cerebral hyperperfusion • Pattern of circle of Willis, ASL perfusion features, and whole brain perfusion volume ratio are potential predicting markers for hyperperfusion after carotid revascularization.

Completeness of circle of Willis and white matter hyperintensities in patients with severe internal carotid artery stenosis.

BACKGROUND: We investigated whether completeness of the circle of Willis (CoW) protected patients with severe internal carotid artery (ICA) stenosis against white matter hyperintensities (WMHs). METHODS: We included 115 patients with unilateral ICA stenosis ≥ 70%. The completeness of CoW was assessed and WMHs were rated on a visual scale. The score of deep and periventricular WMHs was compared between patients with complete and incomplete CoW and between the two hemispheres, ipsilateral and contralateral to stenosed ICA. RESULTS: We included 115 patients with severe ICA stenosis, 60 patients had a complete CoW (52.17%) and 55 had an incomplete CoW (47.83%). The patients with incomplete CoW had higher score of deep WMHs (OR = 1.82, 95% CI 1.08-3.06, P = 0.023) and periventricular WMHs (OR = 4.53, 95% CI 2.09-9.81, P = 0.000) than those with complete CoW. In the patients with incomplete CoW, the score of deep WMHs (OR = 4.14, 95% CI 1.33-12.93, P = 0.014) and periventricular WMHs (OR = 5.46, 95% CI 1.16-25.62, P = 0.032) was higher in the hemisphere ipsilateral to stenosed ICA than that in the contralateral hemisphere. In the patients with complete CoW, there was no significant difference in the score of deep WMHs (OR = 2.10, 95% CI 0.37-11.91, P = 0.401) and periventricular WMHs (OR = 2.83, 95% CI 0.99-8.05, P = 0.051) between the ipsilateral and contralateral hemispheres to stenosed ICA. CONCLUSION: The completeness of CoW protected patients with severe ICA stenosis against WMHs.

Iatrogenic pseudoaneurysm rupture of the anterior cerebral artery after placement of an external ventricular drain, treated with clip-wrapping: a case report and review of the literature.

External ventricular drains (EVDs) are often placed emergently for patients with hydrocephalus, which carries a risk of hemorrhage. Rarely, rupture of a pseudoaneurysm originating from an EVD placement precipitates such a hemorrhage. An EVD was placed in a patient with a ruptured left posterior communicating artery aneurysm who later underwent endovascular coil embolization. On post-bleed day 20, a distal right anterior cerebral artery pseudoaneurysm along the EVD tract ruptured, which was successfully treated via clip-wrapping. Although EVD-associated pseudoaneurysms are rare, they have a high propensity for rupture. Early treatment of these lesions should be considered to prevent neurologic deterioration.

The vascular patterns of the posterior part of the circulus arteriosus cerebri (Willisi).

BACKGROUND: Various authors defined three patterns of the posterior part of the circulus arteriosus cerebri Willisi (CW) according to the diameter of the posterior communicating artery (PCoA) and the precommunicating segment of the posterior cerebral artery (P1). In the adult pattern, the P1 has a diameter larger than the non-hypoplastic PCoA. In the transitional pattern, the diameter of the PCoA is equal to that of the P1. In the fetal pattern, the diameter of the P1 is smaller than the diameter of the PCoA. The study was aimed to evaluate the configurations and calibers of the posterior part of the CW. METHODS: The work was conducted on 185 adult post-mortem brains. The CW and its branches were photographed by a digital camera. We used the software Image J to evaluate and process the gained images. RESULTS: The fetal pattern was found unilaterally in 8.37 %, and bilaterally in 4.86 %. The transitional pattern was observed unilaterally in 6.47 %, and bilaterally in 1 %. The prevalence of the unilateral and bilateral adult patterns was equal (21.62 % for each configuration). The hypoplastic PCoA was found unilaterally in 17.57 %, and bilaterally in 16.76 %. CONCLUSION: Various factors including genetic and environmental may affect the development of the cerebral vessels and their dimensions. The distinguishing of the vascular dimensions in vivo can help in the expectation and may be the avoidance of possible cerebrovascular disturbances in the future. Correlation and interdisciplinary cooperation of the studies dealing with morphology, radiology, and hemodynamics of the cerebral vessels are becoming an urgent need. The assumed results of this cooperation can be used in tabulating the calibers of the cerebral vessels and determining the threshold dimensions under which failure of hemodynamics and collateral function may appear (Tab. 2, Fig. 5, Ref. 28).

Comparison of 3D magnetic resonance imaging and digital subtraction angiography for intracranial artery stenosis.

OBJECTIVES: To compare three-dimensional high-resolution magnetic resonance imaging (3D HR-MRI) and digital subtraction angiography (DSA) for diagnosing and evaluating stenosis in the entire circle of Willis. METHODS: The study included 516 intracranial arteries from 43 patients with intracranial artery stenosis (ICAS) who underwent both 3D HR-MRI and DSA within 1 month. Two readers independently diagnosed atherosclerosis, dissection, moyamoya disease and vasculitis, rated their diagnostic confidence for each vessel and measured the luminal diameters. Reference standard was made from clinico-radiologic diagnosis. Diagnostic accuracy, diagnostic confidence, the degree of stenosis and luminal diameter were assessed and compared between both modalities. RESULTS: For atherosclerosis, 3D HR-MRI showed better diagnostic accuracy (P = .03-.003), sensitivity (P = .006-.01) and positive predictive value (P ≤ .001-.006) compared to DSA. Overall, the readers were more confident of their diagnosis of ICAS when using 3D HR-MRI (reader 1, P ≤ .001-.007; reader 2, P ≤ .001-.015). 3D HR-MRI showed similar degree of stenosis (P > .05) and higher luminal diameter (P < .05) compared to DSA. CONCLUSIONS: 3D HR-MRI might be useful to evaluate atherosclerosis, with better diagnostic confidence and comparable stenosis measurement compared to DSA in the entire circle of Willis. KEY POINTS: • 3D HR-MRI showed better diagnostic accuracy for atherosclerosiscompared to DSA • 3D HR-MRI showed better overall diagnostic confidence for stenosiscompared to DSA • 3D HR-MRI and DSA showed similar degree of stenosis.

Misinterpretation of ischaemic infarct location in relationship to the cerebrovascular territories.

PURPOSE: Cerebral perfusion territories are known to vary widely among individuals. This may lead to misinterpretation of the symptomatic artery in patients with ischaemic stroke to a wrong assumption of the underlying aetiology being thromboembolic or hypoperfusion. The aim of the present study was to investigate such potential misinterpretation with territorial arterial spin labelling (T-ASL) by correlating infarct location with imaging of the perfusion territory of the carotid arteries or basilar artery. MATERIALS AND METHODS: 223 patients with subacute stroke underwent MRI including structural imaging scans to determine infarct location, time-of-flight MR angiography (MRA) to determine the morphology of the circle of Willis and T-ASL to identify the perfusion territories of the internal carotid arteries, and basilar artery. Infarct location and the perfusion territory of its feeding artery were classified with standard MRI and MRA according to a perfusion atlas, and were compared to the classification made according to T-ASL. RESULTS: A total of 149 infarctions were detected in 87 of 223 patients. 15 out of 149 (10%) infarcts were erroneously attributed to a single perfusion territory; these infarcts were partly located in the originally determined perfusion territory but proved to be localised in the border zone with the adjacent perfusion territory instead. 12 out of 149 (8%) infarcts were misclassified with standard assessments and were not located in the original perfusion territory. CONCLUSIONS: T-ASL with territorial perfusion imaging may provide important additional information for classifying the symptomatic brain-feeding artery when compared to expert evaluation with MRI and MRA.

Skeleton-based cerebrovascular quantitative analysis.

BACKGROUND: Cerebrovascular disease is the most common cause of death worldwide, with millions of deaths annually. Interest is increasing toward understanding the geometric factors that influence cerebrovascular diseases, such as stroke. Cerebrovascular shape analyses are essential for the diagnosis and pathological identification of these conditions. The current study aimed to provide a stable and consistent methodology for quantitative Circle of Willis (CoW) analysis and to identify geometric changes in this structure. METHOD: An entire pipeline was designed with emphasis on automating each step. The stochastic segmentation was improved and volumetric data were obtained. The L1 medial axis method was applied to vessel volumetric data, which yielded a discrete skeleton dataset. A B-spline curve was used to fit the skeleton, and geometric values were proposed for a one-dimensional skeleton and radius. The calculations used to derive these values were illustrated in detail. RESULT: In one example(No. 47 in the open dataset) all values for different branches of CoW were calculated. The anterior communicating artery(ACo) was the shortest vessel, with a length of 2.6mm. The range of the curvature of all vessels was (0.3, 0.9) ± (0.1, 1.4). The range of the torsion was (-12.4,0.8) ± (0, 48.7). The mean radius value range was (3.1, 1.5) ± (0.1, 0.7) mm, and the mean angle value range was (2.2, 2.9) ± (0, 0.2) mm. In addition to the torsion variance values in a few vessels, the variance values of all vessel characteristics remained near 1. The distribution of the radii of symmetrical posterior cerebral artery(PCA) and angle values of the symmetrical posterior communicating arteries(PCo) demonstrated a certain correlation between the corresponding values of symmetrical vessels on the CoW. CONCLUSION: The data verified the stability of our methodology. Our method was appropriate for the analysis of large medical image datasets derived from the automated pipeline for populations. This method was applicable to other tubular organs, such as the large intestine and bile duct.

Completeness of the circle of Willis and risk of ischemic stroke in patients without cerebrovascular disease.

INTRODUCTION: We investigated circle of Willis (CoW) completeness in relation to the risk of future ischemic stroke in patients without prior cerebrovascular disease. METHODS: We included 976 patients with atherosclerotic disease, but no previous TIA/stroke, from the Second Manifestations of ARTerial disease (SMART) study. All patients underwent MR angiography of the CoW. Cox regression was used to determine whether anterior CoW completeness (anterior communicating artery or A1 segments) and posterior CoW completeness (posterior communicating arteries or P1 segments) were related to future stroke, and whether CoW completeness influenced the relation between internal carotid artery (ICA) stenosis/occlusion and future stroke. RESULTS: Thirty patients (3.1 %) had ischemic stroke after 9.2 ± 3.0 years of follow-up. Twenty-four patients (80 %) had anterior circulation stroke. An incomplete anterior CoW was related to future anterior circulation stroke (HR 2.8 (95 % CI 1.3-6.3); p = 0.01), whereas a one-sided and two-sided incomplete posterior CoW were not (HR 2.2 (95 % CI 0.7-7.1; p = 0.19) and 1.9 (95 % CI 0.6-5.9; p = 0.29), respectively). In stratified analyses, patients with an incomplete anterior CoW had the highest risk of future anterior circulation stroke when they also had a one-sided (HR 7.0 (95 % CI 1.3-38.2; p = 0.02)) or two-sided incomplete posterior CoW (HR 5.4 (95 % CI 1.0-27.8; p = 0.04). CoW completeness did not change the relation between asymptomatic ICA stenosis/occlusion and future ischemic stroke (p = 0.68). CONCLUSIONS: An incomplete anterior CoW combined with an incomplete posterior CoW is related to future anterior circulation stroke. CoW completeness has no large effect on the relation between asymptomatic ICA stenosis/occlusion and future stroke.

A 3D numerical study of the collateral capacity of the Circle of Willis with anatomical variation in the posterior circulation.

BACKGROUND: The Circle of Willis (CoW) is the most important collateral pathway of the cerebral artery. The present study aims to investigate the collateral capacity of CoW with anatomical variation when unilateral internalcarotid artery (ICA) is occluded. METHODS: Basing on MRI data, we have reconstructed eight 3D models with variations in the posterior circulation of the CoW and set four different degrees of stenosis in the right ICA, namely 24%, 43%, 64% and 79%, respectively. Finally, a total of 40 models are performed with computational fluid dynamics simulations. All of the simulations share the same boundary condition with static pressure and the volume flow rate (VFR) are obtained to evaluate their collateral capacity. RESULTS: As for the middle cerebral artery (MCA) and the anterior cerebral artery (ACA), the transitional-type model possesses the best collateral capacity. But for the posterior cerebral artery (PCA), unilateral stenosis of ICA has the weakest influence on the unilateral posterior communicating artery (PCoA) absent model. We also find that the full fetal-type posterior circle of Willis is an utmost dangerous variation which must be paid more attention. CONCLUSION: The results demonstrate that different models have different collateral capacities in coping stenosis of unilateral ICA and these differences can be reflected by different outlets. The study could be used as a reference for neurosurgeon in choosing the best treatment strategy.

The role of the circle of Willis in internal carotid artery stenosis and anatomical variations: a computational study based on a patient-specific three-dimensional model.

BACKGROUND: The aim of this study is to provide better insights into the cerebral perfusion patterns and collateral mechanism of the circle of Willis (CoW) under anatomical and pathological variations. METHODS: In the current study, a patient-specific three-dimensional computational model of the CoW was reconstructed based on the computed tomography (CT) images. The Carreau model was applied to simulate the non-Newtonian property of blood. Flow distributions in five common anatomical variations coexisting with different degrees of stenosis in the right internal carotid artery (RICA) were investigated to obtain detailed flow information. RESULTS: With the development of stenosis in unilateral internal carotid artery (ICA), the cerebral blood supply decreased when the degree of stenosis increased. The blood supply of the ipsilateral middle cerebral artery (MCA) was most affected by the stenosis of ICA. The anterior communicating artery (ACoA) and ipsilateral posterior communicating artery (PCoA) functioned as the important collateral circulation channels when unilateral stenosis occurred. The blood flow of the anterior circulation and the total cerebral blood flow (CBF) reached to the minimum in the configuration of the contralateral proximal anterior cerebral artery (A1) absence coexisting with unilateral ICA stenosis. CONCLUSIONS: Communicating arteries provided important collateral channels in the complete CoW when stenosis in unilateral ICA occurred. The cross-flow in the ACoA is a sensitive indicator of the morphological change of the ICA. The collateral function of the PCoA on the affected side will not be fully activated until a severe stenosis occurred in unilateral ICA. The absence of unilateral A1 coexisting with the stenosis in the contralateral ICA could be the most dangerous configuration in terms of the total cerebral blood supply. The findings of this study would enhance the understanding of the collateral mechanism of the CoW under different anatomical variations.