Study on the correlation between the circle of Willis structure and collateral circulation in bilateral carotid artery occlusion

Background and purpose

Bilateral carotid artery occlusion (CAO) is a rare condition and the collateral circulation is more complicated than in unilateral CAO. The circle of Willis (CoW) is the most important collateral circulation compensation pathway in CAO. However, the specific role of CoW in the collateral circulation compensation pathway of CAO has not been fully elucidated. The purpose of this study is to investigate the role of CoW in the collateral circulation compensation pathway of CAO.

Materials and methods

Clinical, imaging, and hemodynamic data of 30 patients with bilateral CAO were collected to analyze the collateral blood flow compensation pathway and its characteristics, and to examine the correlation between the structure of the CoW and the collateral circulation of bilateral CAO.

Results

This paper summarized 30 patients with bilateral CAO. There were 0 cases of the CoW complete type, 18 cases of the partially complete type (60%), and 12 cases of the incomplete type (40%). For the partially complete type cases, there were 14 complete anterior circulation cases (46.7%). The collateral circulation collateral circulation pathway included 14 cases with anterior communicating artery(ACoA), 7 cases with posterior cerebral artery (PCA)-middle cerebral artery (MCA) leptomeningeal anastomosis (LMA), 5 cases with ophthalmic artery(OA), 3 cases with lateral posterior communicating artery(PCoA), 1 case with internal carotid artery (ICA) stealing, 1 case with new Moyamoya vessels, and 4 cases of other types. There were four cases (13.3%) with complete posterior circulation, including four cases with bilateral PCoA, three cases with PCA-MCA LMA, and two cases with OA. There were 12 cases (40%) with incomplete CoW, including 8 cases with PCA-MCA LMA, 3 cases with lateral PCoA, 1 case with anterior cerebral artery (ACA)-MCA LMA, 4 cases with OA, and 1 other case.

Conclusion

The collateral circulation pathway differs among patients with different CoW structure types. When the CoW is partially complete, it mainly provides blood flow compensation to the ischemic area through primary collateral circulation. When the CoW is incomplete, it mainly provides blood flow compensation to the ischemic area through secondary collateral circulation.

Variants of the circle of Willis in ischemic stroke patients

PURPOSE

We aim to provide prevalence and pattern of anatomical variants of circle of Willis in over one thousand ischemic stroke patients compared to an age- and sex-matched control group, and to determine their role in the severity and in-hospital prognosis.

METHODS

Two groups of neuroradiologists evaluated all vascular images of ischemic stroke patients and controls to identify anatomical variants using a preexisted classification. We collected data concerning patient characteristics, stroke severity on admission and discharge, in-hospital mortality, hemorrhagic transformation, acute treatment performed, and etiology.

RESULTS

We included 1131 patients with acute ischemic stroke and 562 controls. Among stroke patients, 702 (62.1%) had one or more vascular variants, compared to 308 (54.8%) of the control group (p < 0.01), 165/702 (23.5%) had an anterior circulation variant only, 384/702 (54.7%) had a posterior circulation variant only, and 153/702 (21.8%) patients had variants in both anterior and posterior circulation. Patients with variants were older (69.7 ± 13.9 years vs 72.0 ± 12.9 years; p = 0.039). The most prevalent variant was the agenesis/hypoplasia of the ACA (201/1131; 17.8%) followed by the unilateral fetal type of the PCA (137/1131; 12.11%).

CONCLUSIONS

We provided the prevalence and the pattern of the brain vascular variants of the circle of Willis in a cohort of patients with ischemic stroke. The prevalence of variants was higher in stroke patients compared to controls. Patients with variants were older but had no differences in sex, neurological admission severity, hemorrhagic transformation, etiology, and in-hospital outcome compared to patients with a typical circle of Willis.

Morphologic variants of the Cerebral Arterial Circle on computed tomographic angiography (CTA): a large retrospective study

PURPOSE

To confirm and illustrate the great variability of morphology of the Cerebral Arterial Circle (CAC)-also commonly called "Circle of Willis"-in current clinical Computed Tomography Angiography (CTA) practice.

METHODS

Computed Tomographic Angiographic 3D Volume Rendering reconstructions of the CAC performed in a series of 511 patients were retrospectively reviewed and classified following their anatomic configuration.

RESULTS

An amount of 27 CAC configurations were listed. Complete and "nearly complete" (1 missing segment) CACs were found in 115 (22.58%) and 157 (28.6%) patients. The posterior arch was much more frequently incomplete (374 patients = 73.18%) than the anterior arch (96 patients = 18.4%). The main cause was a high prevalence of missing posterior communicating arteries (PCoAs). The left or right PCoA were unilaterally lacking in 156 patients (30.53%) and both PCoAs were lacking in 179 patients (35.02%). Cases with 2 and 3 missing segments were observed in 184 (36%) and 44 patients (8.6%). Precarious situations were also identified including 7 cases (1.4%) of complete isolation of the middle cerebral artery (MCA), 11 cases (2.15%) of absence of interhemispheric supply, 205 cases (40.1%) of full separation of the carotid and vertebra-basilar (VB) territories and 44 cases (8.6%) of full separation of the three main arterial axes (both ICAs and VB). The prevalence of Fetal Posterior Cerebral Arteries (FPCA) variants was also reported. A "Full" FPCA was found unilaterally in 48 (9.4%) and bilaterally in 13 (2.54%) of patients. Apart from agenesis and hypoplasia reported in our study, various other variations of the anterior complex of the CAC (ACoA and A2 segments of the ACA) were also noted.

CONCLUSION

CTA with 3D Volume Rendering may powerfully assess the numerous variations of the CAC. This assessment is of prime importance for the evaluation of patients presenting with risk factors or in whom neurosurgery, cardiac surgery, interventional radiology or carotid endarterectomy (CEA) are being considered.

Posterior Cerebral Circulation Stroke Secondary to Foetal Origin of Posterior Communicating Artery: An Indication for Carotid Endarterectomy

Introduction

Posterior cerebral circulation strokes are most commonly caused by posterior vasculature in situ thrombosis, cardiac emboli, or arterial dissection. However, the foetal origin of the posterior communicating artery is an anatomical variant of the cerebral circulation that results in communication between the internal carotid and posterior cerebral circulation. Therefore, rarely this can result in posterior cerebral territory infarction from internal carotid artery thrombo-embolism. This is the report of a case in which a patient suffered posterior circulation stroke secondary to this anatomical variation of the circle of Willis.

Report

A 71 year old male patient was admitted to the stroke team with seizures, headache, and confusion. Examination revealed a left sided homonymous hemianopia. Diffusion weighted magnetic resonance imaging (MRI) of the brain 36 hours into his admission revealed an acute right posterior circulation infarct with extensive haemorrhagic transformation. Duplex ultrasound three days later revealed a heavily calcified right internal carotid artery mixed echogenicity plaque with 80%-90% stenosis. Subsequent computed tomography angiography showed a large right foetal variant posterior communicating artery. Following improvement in functional status, the patient underwent uneventful carotid endarterectomy to reduce risk of future stroke.

Discussion

In patients presenting with posterior circulation infarction, clinicians should consider embolism from an atheromatous internal carotid artery via the variant foetal origin of posterior communicating artery. If detected, consideration should be given to undertaking carotid endarterectomy to reduce future stroke risk if no other source is detected.

Mechanical Thrombectomy for Acute Intracranial Carotid Occlusion with Patent Intracranial Arteries : The Italian Registry of Endovascular Treatment in Acute Stroke

PURPOSE

Intracranial carotid artery occlusion represents an underinvestigated cause of acute ischemic stroke as well as an indication for mechanical thrombectomy. We investigated baseline and procedural characteristics, outcomes and predictors of outcome in patients with acute ischemic stroke secondary to intracranial carotid artery occlusion.

METHODS

A retrospective analysis of the Italian Registry of Endovascular Treatment in Acute Stroke was performed. Patients with intracranial carotid artery occlusion (infraclinoid and supraclinoid) with or without cervical artery occlusion but with patent intracranial arteries were included. The 3‑month functional independence, mortality, successful reperfusion and symptomatic intracranial hemorrhage were evaluated.

RESULTS

Intracranial carotid artery occlusion with patent intracranial arteries was diagnosed in 387 out of 4940 (7.8%) patients. The median age was 74 years and median baseline National Institute of Health Stroke Scale (NIHSS) was 18. Functional independence was achieved in 130 (34%) patients, successful reperfusion in 289 (75%) and symptomatic intracranial hemorrhage in 33 (9%), whereas mortality occurred in 111 (29%) patients. In univariate analysis functional independence was associated with lower age, lower NIHSS at presentation, higher rate of successful reperfusion and lower rate of symptomatic intracranial hemorrhage. Multivariable regression analysis found age (odds ratio, OR:1.03; P = 0.006), NIHSS at presentation (OR: 1.07; P < 0.001), diabetes (OR: 2.60; P = 0.002), successful reperfusion (OR:0.20; P < 0.001) and symptomatic intracranial hemorrhage (OR: 4.17; P < 0.001) as the best independent predictors of outcome.

CONCLUSION

Our study showed a not negligible rate of intracranial carotid artery occlusion with patent intracranial arteries, presenting mostly as severe stroke, with an acceptable rate of 3‑month functional independence. Age, NIHSS at presentation and successful reperfusion were the best independent predictors of outcome.

Subvoxel vessel wall thickness measurements of the intracranial arteries using a convolutional neural network

Vessel wall thickening of the intracranial arteries has been associated with cerebrovascular disease and atherosclerotic plaque development. Visualization of the vessel wall has been enabled by recent advancements in vessel wall MRI. However, quantifying early wall thickening from these MR images is difficult and prone to severe overestimation, because the voxel size of clinically used acquisitions exceeds the wall thickness of the intracranial arteries. In this study, we aimed for accurate and precise subvoxel vessel wall thickness measurements. A convolutional neural network was trained on MR images of 34 ex vivo circle of Willis specimens, acquired with a clinically used protocol (isotropic acquired voxel size: 0.8 mm). Ground truth measurements were performed on images acquired with an ultra-high-resolution protocol (isotropic acquired voxel size: 0.11 mm) and were used for evaluation. Additionally, we determined the robustness of our method by applying Monte Carlo dropout and test time augmentation. Lastly, we applied our method on in vivo images of three intracranial aneurysms to measure their wall thickness. Our method shows resolvability of different vessel wall thicknesses, well below the acquired voxel size. The method described may facilitate quantitative measurements on MRI data for a wider range of clinical applications.

Incidence of hypoplastic posterior communicating artery and fetal posterior cerebral artery in Andhra population of India: a retrospective 3-Tesla magnetic resonance angiographic study

The posterior communicating arteries (PCoA) are important component of collateral circulation between the anterior and posterior part of circle of Willis (CW). The hypoplasia or aplasia of PCoA will reflect on prognosis of the neurological diseases. Precise studies of the incidence of hypoplastic PCoA in Andhra Pradesh population of India are hitherto unreported, since the present study was undertaken. Two hundred and thirty one magnetic resonance angiography (MRA) images were analyzed to identify the hypoplasia of PCoA and presence of fetal type of posterior cerebral artery (f-PCA) in patients with different neurological symptoms. All the patients underwent 3.0T MRI exposure. The results were statistically analysed. A total of 63 (27.3%) PCoA hypoplasia and 13 cases with f-PCA (5.6%) cases were identified. The hypoplastic PCoA was noted more in males than females (P<0.05) and right side hypoplasia was common than the left (P<0.04); bilateral hypoplasia of PCoA was seen in 37 cases out of 63 and is significant. The hypoplastic cases of the present study also were associated with variations of anterior cerebral arteries and one case was having vertebral artery hypoplasia. Incidence of PCoA as unilateral or bilateral with other associated anomalies of CW is more prone to develop stroke, migraine and cognitive dysfunction. Knowledge of these variations in the PCoA plays a pivotal role in diagnoses of neurological disorders and in neurovascular surgeries and angiographic point of view.

Cerebrovacular Reserve Predicts the Cerebral Hyperperfusion Syndrome After Carotid Endarterectomy

BACKGROUND

Cerebral hyperperfusion syndrome is a rare but potentially severe complication of carotid artery revascularisation that develops under conditions of resistant postoperative hypertension and impaired cerebrovascular autoregulation.

OBJECTIVE

Was to determine which preoperative and operative factors affect the development of cerebral hyperperfusion syndrome after carotid endarterectomy.

METHODS

This prospective observational study enrolled 93 asymptomatic patients who underwent carotid endarterectomy. Cerebral hyperperfusion was registered in patients who had 100% postoperative increase in mean flow in middle cerebral artery registered by Transcranial Doppler ultrasound. Cerebral hyperperfusion syndrome was diagnosed in patients with cerebral hyperperfusion who postoperatively developed at least one of the symptoms. Pre-operative and operative risk factors for cerebral hyperperfusion syndrome were analysed by multivariate binary logistic regression.

RESULTS

Out of 93 operated patients, cerebral hyperperfusion was registered in 23 and cerebral hyperperfusion syndrome in 18 patients. Risk factors for cerebral hyperperfusion syndrome were included in the binary logistic regression model. Incomplete Circle of Willis morphology on 3D TOF magnetic resonance image (p = 0.002), Breath holding index below the 0.69 cut-off (p = 0.006), positive criteria for insufficient collateral flow through circle of Willis registered by TCD (p = 0.03), and poorly controlled hypertension (p = 0.023) showed statistically significant independent predictive value for cerebral hyperperfusion syndrome. The model was statistically significant (p = 0.012) and correctly classified 90.3 % of patients.

CONCLUSIONS

Incomplete circle of Willis and insufficient collateral flow, low cerebrovascular reserve, and poorly regulated hypertension are significant predictors of post- carotid endarterectomy hyperperfusion development.

Predictors of Successful First-Pass Thrombectomy with a Balloon Guide Catheter: Results of a Decision Tree Analysis

Complete recanalization after a single retrieval maneuver is an interventional goal in acute ischemic stroke and an independent factor for good clinical outcome. Anatomical biomarkers for predicting clot removal difficulties have not been comprehensively analyzed and await unused. We retrospectively evaluated 200 consecutive patients who suffered acute stroke and occlusion of the anterior circulation and were treated with mechanical thrombectomy through a balloon guide catheter (BGC). The primary objective was to evaluate the influence of carotid tortuosity and BGC positioning on the one-pass Modified Thrombolysis in Cerebral Infarction Scale (mTICI) 3 rate, and secondarily, the influence of communicating arteries on the angiographic results. After the first-pass mTICI 3, recanalization fell from 51 to 13%. The regression models and decision tree (supervised machine learning) results concurred: carotid tortuosity was the main constraint on efficacy, reducing the likelihood of mTICI 3 after one pass to 30%. BGC positioning was relevant only in carotid arteries without elongation: BGCs located in the distal internal carotid artery (ICA) had a 70% probability of complete recanalization after one pass, dropping to 43% if located in the proximal ICA. These findings demonstrate that first-pass mTICI 3 is influenced by anatomical and interventional factors capable of being anticipated, enabling the BGC technique to be adapted to patient’s anatomy to enhance effectivity.

Surgical correction of coarctation of the aorta featuring an incomplete circle of Willis

Although devastating complications during simple coarctation of aorta repair now occur less frequently, some unique cases still require extra caution. Here, we report a case of coarctation of the aorta with a rare anomaly in the circle of Willis and an aberrant right subclavian artery, which required a thorough surgical strategy that prevented cerebral malperfusion.

Repaired coarctation of the aorta, persistent arterial hypertension and the selfish brain

BACKGROUND

It has been estimated that 20-30% of repaired aortic coarctation (CoA) patients develop hypertension, with significant cardiovascular morbidity and mortality. Vertebral artery hypoplasia (VAH) with an incomplete posterior circle of Willis (ipCoW; VAH + ipCoW) is associated with increased cerebrovascular resistance before the onset of increased sympathetic nerve activity in borderline hypertensive humans, suggesting brainstem hypoperfusion may evoke hypertension to maintain cerebral blood flow: the "selfish brain" hypothesis. We now assess the "selfish brain" in hypertension post-CoA repair.

METHODS

Time-of-flight cardiovascular magnetic resonance angiography from 127 repaired CoA patients (34 ± 14 years, 61% male, systolic blood pressure (SBP) 138 ± 19 mmHg, diastolic blood pressure (DBP) 76 ± 11 mmHg) was compared with 33 normotensive controls (42 ± 14 years, 48% male, SBP 124 ± 10 mmHg, DBP 76 ± 8 mmHg). VAH was defined as < 2 mm and ipCoW as hypoplasia of one or both posterior communicating arteries.

RESULTS

VAH + ipCoW was more prevalent in repaired CoA than controls (odds ratio: 5.8 [1.6-20.8], p = 0.007), after controlling for age, sex and body mass index (BMI). VAH + ipCoW was an independent predictor of hypertension (odds ratio: 2.5 [1.2-5.2], p = 0.017), after controlling for age, gender and BMI. Repaired CoA subjects with VAH + ipCoW were more likely to have difficult to treat hypertension (odds ratio: 3.3 [1.01-10.7], p = 0.049). Neither age at time of CoA repair nor any specific repair type were significant predictors of VAH + ipCoW in univariate regression analysis.

CONCLUSIONS

VAH + ipCoW predicts arterial hypertension and difficult to treat hypertension in repaired CoA. It is unrelated to age at time of repair or repair type. CoA appears to be a marker of wider congenital cerebrovascular problems. Understanding the "selfish brain" in post-CoA repair may help guide management.

JOURNAL SUBJECT CODES

High Blood Pressure; Hypertension; Magnetic Resonance Imaging (MRI); Cardiovascular Surgery; Cerebrovascular Malformations.

Isolated left vertebral artery and its consequences for aortic arch repair

A left vertebral artery (LVA) originating directly from the aortic arch is the second most common supra-aortic branching anomaly. This isolated LVA can also terminate in the posterior inferior cerebellar artery without contributing to the circle of Willis, limiting treatment options, especially in cases with an incomplete circle. Here, we describe our consideration of the treatment options for a 79-year-old patient with a large distal aortic arch aneurysm combined with an isolated LVA and incomplete circle of Willis that may endanger adequate (intraoperative) cerebral perfusion.

Fetal origin of posterior cerebral artery related to poor collaterals in patients with acute ischemic stroke

The anatomic variation of Circle of Willis (CW) has been shown to have a great impact on its compensatory capacity during acute ischemic stroke. The purpose of the study was to evaluate the effect of variations in CW on collateral circulation in patients with acute ischemic stroke who had major artery occlusion. Patients with acute ischemic stroke within 4.5 h of stroke onset who had at least moderate severity of stroke (NIHSS ≥ 6), caused by major artery occlusion were included. Multiphase computed tomography angiography (CTA) was performed. Variations in CW on each patient were recorded and compared between those with poor collateral and intermediate-good collateral circulation. There were 66 patients. Mean NIHSS was 15. Forty patients had poor collateral circulation and 26 patients had intermediate-good collateral circulation. There were variations in CW: no visualized posterior communicating artery (PCOM) (31/66, 47%), fetal origin of posterior cerebral artery (25/66, 38%), one anterior cerebral artery, segment A1 (A1) hypoplasia or atresia (16/66, 24%), one PCOM (8/66, 12%), and complete CW (3/66, 5%). Fetal origin of posterior cerebral artery (PCA) was associated with poor collateral circulation (48% vs 23%, p-value = 0.046). This pilot study showed that the presence of fetal origin of PCA was associated with poor collateral circulation in patients with acute ischemic stroke caused by major artery occlusion.

Descriptive Analysis of Cerebral Arterial Vascular Architecture in Dromedary Camel (Camelus dromedarius)

The artiodactyl brain has multiple levels of vascular pooling and the rostral epidural rete mirabile (RERM) at its base. The current study is the first of its kind to precisely demonstrate the arterial vasculature of the dromedary brain, utilizing a new casting method with colored latex and epoxy paint. In total, 35 freshly slaughtered dromedary heads were injected with colored latex or colored epoxy paint prior to dissection in order to reveal cerebral vasculature; Ten processed heads were chemically digested with 5% potassium hydroxide to obtain hard casts of cerebral arteries and anastomosing structures. The outcomes of this study ascertain the distinct vascular features of dromedaries that set them apart from other artiodactyls. In addition to the RERM, the dromedary possesses a well-developed ophthalmic and chiasmatic rete. The dromedary is similar to giraffe, goat, cat and pig in the contribution of middle meningeal artery to the rete mirabile; however, dromedaries have several arteries emerging directly from the cerebral arterial circle that supply the choroid plexus and pineal gland. Additionally, dromedaries exhibit a dominant basilar system that dominates the blood supply to the medulla oblongata, pons, and cerebellum. In our study, we were able to graphically prove the lack of connection between the areas supplied by vertebrobasilar system and carotid system in the dromedary. Furthermore, the vertebral artery does not branch into the basilar artery; instead, it acts as a contributing vessel to the ventral spinal artery that later fuse to form the basilar artery. This study employed the new casting method to illustrate a new arterial source to RERM and the various anastomoses among arterial sources supplying the brain in the dromedary. These anastomoses play an important role in maintaining an uninterrupted cerebral blood supply, decreasing the vulnerability of the fragile brain against ischemia and stroke, as well as, play an important role in maintaining blood pressure and flow in long-necked dromedaries when they raise or lower their heads.

Histological Differences of the Vascular Wall Between Sites With High and Low Prevalence of Intracranial Aneurysm

Intracranial aneurysms (IAs) develop more often on bifurcations compared with the rest of the circle of Willis (CoW). We investigated histological differences between 2 high IA prevalence sites (anterior communicating artery [AcomA] and basilar tip) and 2 corresponding low IA prevalence sites (anterior cerebral artery [ACA] and basilar artery [BA]) using histological sections of 10 CoWs without IAs. Medial defect density in the AcomA was 0.24 medial defects/mm compared with 0.02 for the A1 part and 0.03 for the A2 part of the ACA. In the basilar tip we found 0.15 medial defects/mm compared with 0.14 in the BA. Vascular smooth muscle cells (VSMCs) were more often disorganized in both high-prevalence sites (AcomA: 10/10, basilar tip: 5/10) compared with low-prevalence sites (both ACA and BA: 1/10). Intima thickening was more severe in the high-prevalence sites. Vascular wall thickness was not significantly different between high- and low-prevalence sites, but had a larger variance in high- compared with low-prevalence sites (AcomA vs ACA: p = 6.8E-12, basilar tip vs BA: p = 0.02). Disorganized VSMCs at high-prevalence sites likely result in a higher susceptibility to hemodynamic stress, leading to more vascular remodeling (such as intima thickening), which could increase the likelihood of IA formation.

Effect of Fetal Posterior Circulation on Efficacy of Flow Diversion for Treatment of Posterior Communicating Artery Aneurysms: A Multi-Institutional Study

BACKGROUND

Flow diversion (FD) has emerged as an effective treatment modality for aneurysms of the posterior communicating artery (PCOM). Whether or not a fetal posterior circulation (FPC) affects PCOM aneurysm occlusion rates after FD remains undetermined.

METHODS

We performed a retrospective cohort study in which treatment outcomes for FD of PCOM aneurysms from multiple institutions were reviewed. The primary outcome of interest was complete aneurysm occlusion at last follow-up. The presence of a FPC, defined as a PCOM diameter larger than that of the P1 segment, was noted and its relationship to complete aneurysm occlusion was investigated using a Cox proportional hazards model.

RESULTS

There were 49 patients with 49 PCOM aneurysms treated with FD who met inclusion criteria for analysis. A FPC was present in 16 patients (32.7%). Complete aneurysm occlusion was observed in 34 patients (69.4%). Complete occlusion was less common for patients with a FPC (43.7% vs. 81.8%; P = 0.007). For patients with and without a FPC, median time to occlusion was 51 and 6 months, respectively (P = 0.002). Using a multivariable Cox proportional hazards model, a FPC was associated with reduced odds of complete occlusion on last follow-up (risk ratio 0.35, 95% confidence interval 0.14-0.89; P = 0.029).

CONCLUSIONS

Our results indicate reduced efficacy of FD for the treatment of PCOM aneurysms associated with a FPC. These findings may influence treatment selection for aneurysms at this location.

Genetic and Environmental Contributions to Variation in the Posterior Communicating Collaterals of the Circle of Willis

Variation in blood flow mediated by the posterior communicating collateral arteries (PComs) contributes to variation in the severity of tissue injury in obstructive disease. Evidence in animals and humans indicates that differences in the extent of PComs, i.e., their anatomic lumen diameter and whether they are present bilaterally, unilaterally, or absent, are a major factor. These differences arise during development since they are present at birth. However, the causal mechanisms are unknown. We used angiography after maximal dilation to examine involvement of genetic, environmental, and stochastic factors. The extent of PComs varied widely among seven genetically diverse strains of mice. Like pial collaterals in the microcirculation, aging and hypertension reduced PCom diameter, while in contrast, obesity, hyperlipidemia, metabolic syndrome, and diabetes mellitus had no effect. Naturally occurring intrauterine growth restriction had no effect on extent of PCom or pial collaterals in the adult. The number and diameter of PComs evidenced much larger apparent stochastic-dependent variation than pial collaterals. In addition, both PComs underwent flow-mediated outward remodeling after unilateral permanent MCA occlusion that varied with genetic background and was greater on the ipsilesional side. These findings indicate that variation in the number and diameter of PCom collateral arteries arises from stochastic factors and naturally occurring genetic variants that differ from those that cause variation in pial collateral arterioles. Environmental factors also contribute: aging and hypertension reduce PCom diameter. Our results suggest possible sources of variation of PComs in humans and provide information relevant when studying mouse models of occlusive cerebrovascular disease.

An In-Vitro Flow Study Using an Artificial Circle of Willis Model for Validation of an Existing One-Dimensional Numerical Model

A one-dimensional (1D) numerical model has been previously developed to investigate the hemodynamics of blood flow in the entire human vascular network. In the current work, an experimental study of water-glycerin mixture flow in a 3D-printed silicone model of an anatomically accurate, complete circle of Willis (CoW) was conducted to investigate the flow characteristics in comparison with the simulated results by the 1D numerical model. In the experiment, the transient flow and pressure waveforms were measured at 13 selected segments within the flow network for comparisons. In the 1D simulation, the initial parameters of the vessel network were obtained by a direct measurement of the tubes in the experimental setup. The results verified that the 1D numerical model is able to capture the main features of the experimental pressure and flow waveforms with good reliability. The mean flow rates measurement results agree with the predictions of the 1D model with an overall difference of less than 1%. Further experiment might be needed to validate the 1D model in capturing pressure waveforms.

Safety and Efficacy of the Pipeline Embolization Device Use in the Outside Circle of Willis Located Intracranial Aneurysms: A Single-Center Experience

Background

The use of Pipeline Embolization Device (PED) is approved by the US Food and Drug Administration (FDA) to treat aneurysms located between the petrous and superior hypophyseal segments of the internal carotid artery. The purpose of this study is to evaluate the feasibility and efficacy of treating aneurysms outside the FDA approved anatomical locations. Furthermore, we analyze the safety of our antiplatelet protocol.

Methods

Data on all patients treated with PED at our center from March 2015 to December 2017 were reviewed. Only patients with aneurysms treated with PED as off label use were included. Procedural complications and long-term functional outcome measured by modified Rankin Scale (mRS) were recorded. Tirofiban maintenance infusion was administered intravenously after PED deployment. None of the patients had platelet function testing.

Results

A total of 36 patients harboring 36 aneurysms were included in the study. Mean age was 58.2 years ±14.6. Nineteen were women (52.8%) and most aneurysms were unruptured (80.6%). There were no intraoperative complications. Five patients experienced postoperative complications - 4 ischemic strokes and one groin hematoma. None led to any significant disability at follow-up. Thirty-one patients (86.1%) achieved an mRS of 0-2 at follow-up. A Raymond-Roy classification of 1 was achieved in 78.9% of patients.

Conclusion

The use of PED to treat aneurysms located outside the circle of Willis is feasible and effective. Our novel antiplatelet protocol did not require platelet function assay testing and did not lead to a higher rate of thrombo-embolic events compared to what has been previously reported.

Accuracy of blood flow assessment in cerebral arteries with 4D flow MRI: Evaluation with three segmentation methods

Background

Accelerated 4D flow MRI allows for high‐resolution velocity measurements with whole‐brain coverage. Such scans are increasingly used to calculate flow rates of individual arteries in the vascular tree, but detailed information about the accuracy and precision in relation to different postprocessing options is lacking.

Purpose

To evaluate and optimize three proposed segmentation methods and determine the accuracy of in vivo 4D flow MRI blood flow rate assessments in major cerebral arteries, with high‐resolution 2D PCMRI as a reference.

Study Type

Prospective.

Subjects

Thirty‐five subjects (20 women, 79 ± 5 years, range 70–91 years).

Field Strength/Sequence

4D flow MRI with PC‐VIPR and 2D PCMRI acquired with a 3 T scanner.

Assessment

We compared blood flow rates measured with 4D flow MRI, to the reference, in nine main cerebral arteries. Lumen segmentation in the 4D flow MRI was performed with k‐means clustering using four different input datasets, and with two types of thresholding methods. The threshold was defined as a percentage of the maximum intensity value in the complex difference image. Local and global thresholding approaches were used, with evaluated thresholds from 6–26%.

Statistical Tests

Paired t‐test, F‐test, linear correlation (P < 0.05 was considered significant) along with intraclass correlation (ICC).

Results

With the thresholding methods, the lowest average flow difference was obtained for 20% local (0.02 ± 15.0 ml/min, ICC = 0.97, n = 310) or 10% global (0.08 ± 17.3 ml/min, ICC = 0.97, n = 310) thresholding with a significant lower standard deviation for local (F‐test, P = 0.01). For all clustering methods, we found a large systematic underestimation of flow compared with 2D PCMRI (16.1–22.3 ml/min).

Data Conclusion

A locally adapted threshold value gives a more stable result compared with a globally fixed threshold. 4D flow with the proposed segmentation method has the potential to become a useful reliable clinical tool for assessment of blood flow in the major cerebral arteries.

Level of Evidence: 2

Technical Efficacy: Stage 2

J. Magn. Reson. Imaging 2019;50:511–518.

Magnetic resonance angiography determined variations in the circle of Willis: Analysis of a large series from a single center

Objective

The purpose of this study is to evaluate and describe the prevalence and patterns of arterial variants in the circle of Willis (CW) seen in noncontrast three-dimensional time-of-flight magnetic resonance angiography in a series of patients with cerebral vascular accidents (CVAs).

Materials and Methods

A descriptive study was undertaken in 200 patients who presented for screening for CVA in the Department of Radiodiagnosis and Imaging, St. John's Medical College Hospital, Bengaluru, from September 2014 to September 2016.

Results

The most common types of CW in a single subject were anterior variant Type A and posterior variant Type E. Type A in the anterior circulation is the normal adult pattern. There is a single anterior communicating artery. The internal carotid artery bifurcates into the precommunicating segment of the anterior cerebral artery and middle cerebral artery. Type E in the posterior circulation is hypoplasia or absence of both posterior communicating arteries and isolation of the anterior and posterior parts of the circle at this level. Overall, CW variants were slightly more common in women than in men.

Conclusion

Our findings show that the configuration of the CW may vary greatly in the general population. The wide range in the morphology of CW warrants further research on various races and larger populations to confirm the influence of genetic, regional, environmental, and hemodynamic factors or their combination.

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.

Assessment of the Prevalence of Vascular Anomalies of the Circle of Willis Based on the Autopsy of Cadavers in Kurdish Race Between 2016 and 2017

Introduction:

Cerebral arterial variations are commonly associated with cerebrovascular disease and should be considered during brain surgeries. Since some cerebrovascular diseases are seen in certain breeds, it seems that different distributions of cerebral arterial variations depend on race.

Aim:

The aim of this study was to determine the random incidence of vascular anomalies of the circle of Willis in autopsy of the cadavers.

Material and Methods:

In this study, 107 autopsy cadavers were examined. The brain was removed from the skull through standard autopsy procedures and with great care, the circles of Willis were evaluated, their main branches were accurately dissected, their anatomy was examined using a glass plate and variations were recorded.

Results:

The mean age of the cadavers was 57.77 years, and 72.9% of them were male. The forms of circle of Willis of the cadavers were categorized according to the Lazort classification, from which 48.6% had form 1,39.3% form 4, and 12.1% form 6. Out of all patients, 51.4% had hypoplasia and 67.3% had asymmetry. There was a significant relationship between asymmetric incidence and the age of cadavers, the incidence of hypoplasia and sex of the cadavers, and the forms of the circle of Willis and the diameter of segment (p<0.05).

Conclusion:

Due to the high incidence of asymmetry (67.3%) and hypoplasia (51.5%), it seems necessary to perform a complete review of the details of cerebrovascular anatomy in any surgical intervention around the circle of Willis, especially in vascular lesions of this area.

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.

Influence of the circle of Willis on leptomeningeal collateral flow in anterior circulation occlusive stroke: Friend or foe?

BACKGROUND

Clinical outcome after large vessel occlusion (LVO) stroke depends on collateral integrity. We aimed to evaluate whether the completeness of the circle of Willis (CoW) and anterior temporal artery (ATA) determines the status of leptomeningeal collaterals (LC) in patients with acute LVO (internal carotid artery (ICA) and middle cerebral artery M1 (MCA) occlusion) treated with endovascular thrombectomy.

PATIENTS AND METHODS

LC, cross-flow through the anterior communicating artery (ACoA), presence of the ipsilateral posterior communicating artery (IpsiPCoA) and presence of the ATA were evaluated using CT angiography. LC was graded as good when ≥50% collateral filling was noted compared to the unaffected hemisphere.

RESULTS

We included 159 patients with a median age of 75 years (IQR 63-82), MCA M1 occlusion in 96 (60%) and good outcome in 68 (45.6%). The LC were good in 129 (81.1%) patients. Complete IpsiPCoA and incomplete ACoA status was inversely associated with good LC in LVO (OR 0.51 (95% CI 0.02-0.07)). A complete CoW was associated with good LC in ICA occlusions, OR 8.4 (p = .025). Good outcome (modified Rankin scale 0-2 at 3 months) was associated with good LC (OR 5.63 (95% CI 1.11-28.4)), small ischemic lesion volume (OR 0.94 (95% CI 0.97-0.98)) and absence of the ACoA and IpsiPCoA (OR 4.47 (95% CI 1.09-18.3)).

CONCLUSIONS

ATA presence was associated with good leptomeningeal collaterals in LVO (OR 8.13 (95% CI 1.69-39.0)) and in MCA M1 patients (OR 7.9 (95% CI 1.7-36.4)). The effect of ATA was most pronounced in MCA M1 occlusions, and that of ACoA was most pronounced in ICA occlusions.

Quantifying Hemodynamic Changes in Moyamoya Disease Based on Two-Dimensional Cine Phase-Contrast Magnetic Resonance Imaging and Computational Fluid Dynamics

OBJECTIVE

To investigate hemodynamic changes in moyamoya disease (MMD) via two-dimensional cine phase-contrast magnetic resonance imaging and computational fluid dynamics.

METHODS

In 18 patients with MMD and 10 healthy control subjects, phase-contrast magnetic resonance imaging was performed to quantify flow rate of main supplying arteries, including internal carotid arteries (ICAs) and vertebral arteries. Mean flow rate in these vessels was adopted as the patient-specific boundary condition for computational fluid dynamics simulation of the circle of Willis in MMD and control groups. Pressure drop in both ICAs and their difference, wall shear stress and secondary flow in the carotid siphon of ICAs, and flow rate and size of posterior communicating arteries (PComAs) were compared between MMD and control groups. Four patients with MMD underwent follow-up scans for longitudinal comparison.

RESULTS

Phase-contrast magnetic resonance imaging data revealed significantly different flow rate in the left ICA and right vertebral arteries between MMD and control groups. Computational fluid dynamics simulation demonstrated similar wall shear stress and similar secondary flow of both ICAs but significantly higher pressure drop in left ICA, higher pressure drop difference between left ICA and right ICA, and higher flow rate in PComAs in patients with MMD compared with control subjects. Significantly increased size of left PComA in patients with MMD was also found. Follow-up results confirmed that the combination of pressure drop difference, flow rate, and size of PComAs can potentially assist long-term prognosis after surgery.

CONCLUSIONS

Pressure drop difference, flow rate, and size of PComAs can be used to evaluate impairments in cerebrovascular reserve and indicate long-term prognosis in MMD.

Are the Variants of the Circle of Willis Determined by Genetic or Environmental Factors? Results of a Twin Study and Review of the Literature

BACKGROUND

Anatomic variants of the circle of Willis (CW) are commonly observed in healthy subjects. Genetic and environmental factors influencing these variants remain unclear. Our aim was to assess the genetic and environmental background affecting variant CW phenotypes.

METHODS

A total of 122 adult healthy twins from the Hungarian Twin Registry (39 monozygotic (MZ) and 22 dizygotic (DZ) pairs, average age 49.7 ± 13.4 years) underwent Time-of-Flight magnetic resonance angiography and transcranial Doppler sonography. We investigated the anterior and posterior CW according to morphological categories. Prevalence and concordance rates of CW variants were calculated. MZ twins discordant for CW variants were analyzed for cardiovascular risk factors and altered blood flow.

RESULTS

Complete CW (45.0%) and bilaterally absent posterior communicating artery (PCoA) (22.5%) were the most prevalent variants in the anterior and posterior CW, respectively. There was no significant difference regarding the prevalence of variants across zygosity except for bilaterally hypoplastic PCoA (p = .02). DZ concordance was higher compared to MZ twins regarding morphological categories of the CW. Cardiovascular risk factors were not significantly associated with variant CW in MZ twins discordant to CW morphology. Flow parameters did not differ significantly among MZ twins discordant to CW variants.

CONCLUSION

CW variants may not be determined by substantial genetic effects and are not influenced by altered blood flow in healthy individuals. Further investigations are needed to identify potential environmental factors affecting these variants.

Hemodynamic Solution Computation and Pathological Analysis in the Circle of Willis

Hemodynamic indexes will change significantly compared to the normal range of many vascular diseases, therefore it is necessary to establish hemodynamic computation model. Blood circulation is periodically forced huge fluid flow network, the heart is generator of the entire fluid network, based on this hemodynamic characteristics, the circle of Willis's structure is simplified from the perspective of network and hemodynamics. According to hemodynamic equations and circuit graph theory, models blood flow network of the periodically forced hemodynamic equation, obtains the approximate solution of the harmonic waves form based on averaging computation. We apply this model in the network of the circle of Willis, which may help explain the development processes of cerebral circulation disease. The simulation results show that computing results consistent with the clinical observation of blood flow changes in cerebral infarction.

Duplication of the middle cerebral artery in a neonate: case report

The middle cerebral artery, a terminal branch of the internal carotid artery, participates greatly in the blood supply of the cerebral cortex and basal nuclei. The aim of this paper is to present a case of middle cerebral artery duplication in a 3-day-old neonate. A brief literature overview in this paper serves to summarize the research on the middle cerebral artery duplication. Also, possible etiology of this anatomical variation will be discussed, together with the embryology of the middle cerebral artery. The arteries of the circle of Willis are affected by numerous neurovascular diseases and the knowledge of these anatomical variations is important in the diagnostic and therapeutic interventions in this field.

Use of Flow Diversion for the Treatment of Distal Circulation Aneurysms: A Multicohort Study

OBJECTIVE

The safety and efficacy of flow diversion for distal circulation aneurysms of the cerebral vasculature has not been well evaluated. The objective of this study was to assess the use of flow diversion for distal circulation aneurysms (defined as at or beyond the M1, P1, and A1 segments of the middle cerebral artery, posterior cerebral artery, and anterior cerebral artery, respectively) in an international multicenter cohort.

METHODS

Clinical and radiologic records from all patients undergoing flow diversion treatment of distal circulation aneurysms at 3 academic centers (2 in the USA and 1 in Europe) from 2014 until 2017 were retrospectively reviewed.

RESULTS

Forty-six patients (mean age, 58.2 years; 33 women) harboring 46 aneurysms who underwent treatment with either the Pipeline Embolization Device (Medtronic Inc., Dublin, Ireland) or the Flow Re-Direction Endoluminal Device (MicroVention, Tustin, California, USA) were included in these analyses. Thirty-four aneurysms (74%) were located in the anterior circulation and 12 (26%) were located in the posterior circulation. With a mean follow-up of 13.0 months, complete (100%) and near-complete (90%-99%) occlusion was noted in 36 aneurysms (78.2%). Angiographic evidence of side branch or perforator vessel coverage was present in 35 aneurysms (76.1%) but was not associated with failure to occlude at follow-up (P = 0.06). All patients had good functional outcomes after treatment (modified Rankin Scale score 0-2). There were 2 cases (4.3%) of perforator vessel stroke and no hemorrhagic complications.

CONCLUSIONS

Flow diversion for aneurysms beyond the circle of Willis has occlusion rates comparable to alternative treatments and low morbidity. The clinical significance of flow limitation through covered side branches requires further investigation.

Incomplete circle of Willis is associated with a higher incidence of neurologic events during carotid eversion endarterectomy without shunting

OBJECTIVE

A complete circle of Willis (CoW) is considered an important collateral network to maintain blood flow during cross-clamping in carotid endarterectomy (CEA). The aim of this study was to evaluate the impact of an incomplete CoW with isolated middle cerebral artery (iMCA) on immediate neurologic events (INEs) after CEA.

METHODS

We prospectively collected the clinical data and outcomes of 902 patients who underwent CEA under general anesthesia between 2013 and 2015. All patients had preoperative computed tomography angiography of the extracranial and intracranial cerebral circulation. Indications were asymptomatic (52%) and symptomatic (48%) carotid artery disease. Patients who had CEA with shunt (n = 35) and those with inadequate intracranial imaging to assess CoW were excluded (n = 322) only. Computed tomography angiography images were reviewed retrospectively and independently by two vascular radiologists who were blinded for treatment outcomes. Imaging assessment included the vertebral and carotid circulation and each segment of the CoW, which was classified as normal, hypoplastic (diameter < 0.8 mm) or absent. The ipsilateral MCA was considered isolated if there was an absence of the anterior and posterior communicating branches from the contralateral carotid or posterior circulations. INE was defined as any transient ischemic attack (TIA) and stroke diagnosed immediately after the procedure.

RESULTS

Of the 545 included patients (331 males; mean age, 69 ± 8 years), 12 (2.2%) had a stroke in the postoperative period. There were 20 INEs (8 strokes and 12 TIAs). A complete CoW was rare; it was only detected in 19 patients (3.5%) and an iMCA was found in 34 patients (6.3%). When at least one collateral circulation was complete (in 330 patients), we observed only four INEs (1.2%). Of the 34 patients with an iMCA, 8 (24%) had INE (6 TIAs and 2 strokes). Overall, iMCA was an independent predictor of INEs (odds ratio, 11.12; 95% confidence interval, 3.57-35.87; P < .001). With logistic regression, the model included hypertension, smoking, diabetes, hyperlipidemia, carotid clamping time (minutes), contralateral significant internal carotid artery stenosis of greater than 90%, ipsilateral significant internal carotid artery stenosis of greater than 90%, preoperative symptoms in 6 months, and iMCA; above iMCA only symptomatic patients had significant risk (odds ratio, 3.34; 95% confidence interval, 1.19-9.73; P = .02), whereas all other parameters were not significant.

CONCLUSIONS

An iMCA carries more than a 10-fold higher the risk of INEs after CEA with cross-clamping without shunt protection. In these patients, routine shunting is recommended to prevent INEs.

Multidetector CT angiography of the Circle of Willis: association of its variants with carotid artery disease and brain ischemia

PURPOSE

(1) to estimate the prevalence of Circle of Willis (CoW) variants in patients undergoing carotid endarterectomy, (2) to correlate these variants to controls and (3) cerebral ischemia depicted by computed tomography (CT).

MATERIALS AND METHODS

After Institutional Review Board approval, data of 544 carotid endarterectomy patients (331 males, mean age 69±8 years) and 196 controls (117 males, mean age 66±11 years) who underwent brain CT and carotid CT angiography (CTA) were retrospectively analysed. Two observers independently classified each CoW segment as normal, hypoplastic (diameter <0.8 mm) or non-visualized. Four groups of CoW variants based on the number of hypoplastic/non-visualized segments were correlated with clinical data (ANOVA, χ² and multivariate logistic regression analysis). Intra- and inter-observer agreement was estimated using Cohen κ statistics.

RESULTS

High prevalence of CoW variants (97%) and compromised CoW (81%) was observed in the study group and significant difference was found in the distribution of CoW variants compared to controls (p<0.001), internal carotid artery (ICA) stenosis being the only independent predictor of CoW morphology (p<0.001). Significant correlation was found between CoW configuration and brain ischemia in the study group (p=0.002). ICA stenosis of ≥90% was associated to higher rate of ipsilateral A1 hypoplasia/non-visualization (p<0.001). Intra- and inter-observer agreement was from substantial to almost perfect (Cohen κ=0.75-1.0).

CONCLUSION

Highly variable CoW morphology was demonstrated in patients undergoing endarterectomy compared to controls. Likely compromised CoW in relation to cerebral ischemia was observed in a large cohort of carotid endarterectomy subjects.

KEY POINTS

• CoW variant distribution significantly differed in the study and control groups (p<0.001). • ICA stenosis was the only independent predictor of CoW morphology (p<0.001). • Severely compromised CoW configuration showed significant association with brain ischemia (p=0.002).

Smaller caliber of the internal carotid artery in patients with ipsilateral aplasia of the A1 segment of the anterior cerebral artery: a study with CTA

To measure the diameter and the transsectional area of the internal carotid arteries (ICA) on CT Angiography (CTA) in patients with aplasia of the A1-segment of the ACA (A1) and in patients with symmetrical A1, the mean diameter and area of the ICA on both sides were measured at a level of 2 cm below the skull base with a commercially available CT software in 41 consecutive patients with aplasia of A1 observed during a 12-month period on CTA and in 41 control patients with symmetrical A1. The mean diameter of the ipsilateral ICA was 3.83 ± 0.60 mm versus 4.86 ± 0.60 mm as mean diameter of the contralateral ICA and versus 4.40 ± 0.60 mm as mean diameter of both ICAs in the control group of patients. The mean area of the ipsilateral ICA was 11.58 ± 3.80 mm² versus 18. 82 ± 7.39 mm² as mean area of the contralateral ICA and versus 15.29 ± 4.42 mm² as mean area of both ICA in the control group of patients. These differences are statistically highly significant. In patients with symmetrical A1, there was no statistical difference between the diameter or area of both internal carotid arteries. In conclusion, in patients with aplasia of A1, the ipsilateral diameter and area of the cervical ICA is smaller than the diameter and area of the contralateral ICA and smaller than the diameter and area of both internal carotid arteries in patients with symmetrical A1.

Investigation of circle of Willis variants and hemodynamic parameters in twins using transcranial color-coded Doppler sonography

Morphological and hemodynamic variations of the circle of Willis (CW) may have an important impact on cerebrovascular events. However, the environmental and genetic influence remains unclear. For this reason we studied the variations and hemodynamic parameters of the CW in twins using transcranial color-coded sonography (TCCS). Sixty-four twins, 19 monozygotic (MZ) and 13 dizygotic (DZ) pairs from the Italian Twin Registry (average age 45.0 ± 13.7 years) underwent TCCS and risk factor assessment. We examined CW morphology and recorded peak systolic velocity (PSV), end-diastolic velocity (EDV) and pulsatility index (PI). Raw heritability was determined for hemodynamic parameters, whereas concordance and discordance rates were calculated for CW morphological variants. A normal CW anatomy was observed in the majority of MZ and DZ twins (76.5% and 92.3%, respectively). The most frequent variant was a missing anterior cerebral artery (ACA). There was no significant difference in the prevalence of most CW variants depending on the zigosity. Concordance rates were low regarding the presence of variant CW anatomy both in MZ and DZ groups (0.14 and 0.00, respectively). Women had a significantly higher PI in vertebral arteries (VA) and in the right ACA (p = 0.01, p = 0.02 and p < 0.01, respectively). An inverse correlation was observed between hemodynamic parameters and age. Morphological variants of the CW do not seem to be heritable; they are most likely determined by environmental factors. In contrast, hemodynamic parameters of the CW are moderately heritable and this might have implications in the management and prevention of cerebrovascular diseases.

Fluid-structure interaction of patient-specific Circle of Willis with aneurysm: Investigation of hemodynamic parameters

BACKGROUND

Circle of Willis (COW) is a network of cerebral artery which continually supplies the brain with blood. Any disturbance in this supply will result in trauma or even death. One of these damages is known as brain Aneurysm. Clinical methods for diagnosing aneurysm can only measure blood velocity; while, in order to understand the causes of these occurrences it is necessary to have information about the amount of pressure and wall shear stress, which is possible through computational models.

OBJECTIVE

In this study purpose is achieving exact information of hemodynamic blood flow in COW with an aneurysm and investigation of effective factors on growth and rupture of aneurysm.

METHODS

Here, realistic three-dimensional models have been produced from angiography images. Considering fluid-structure interaction have been simulated by the ANSYS.CFX software.

RESULTS

Hemodynamic Studying of the COW and intra-aneurysm showed that the WSS and wall tension in the neck of aneurysms for case A are 129.5 Pa, and 12.2 kPa and for case B they are 53.3 Pa and 56.2 kPa, and more than their fundus, thus neck of aneurysm is prone to rupture.

CONCLUSION

This study showed that the distribution of parameters was dependent on the geometry of the COW, and maximum values are seen in areas prone to aneurysm formation.

Evaluation of an ischemic model in ischemia prone and general Mongolian gerbils by neurological symptom, injury, and sex difference

BACKGROUND

In the previous study, we established an ischemia-prone gerbil population (IG), which was selectively bred to increase the incidence of unilateral carotid arterial occlusion (UCO)-induced ischemia in Mongolian gerbils. However, if the characteristics of ischemia model in IG are the same as those in general gerbils (GG), and if the neurological symptoms are associated with the neurological insults in IG is still unclear.

METHODS

In the present study, we evaluated the UCO model in IG by analyzing neurological symptoms, neurological injury in the hippocampal CA1 region and compared with GG.

RESULTS

The data showed that the ratios of neurological symptom scores ≥ 2 in the IG and GG groups were 65.0% vs 30.0%, respectively, and were significantly different (P < .01).The neuronal damage following a UCO ischemic insult in the IG group was more severe compared to the GG group. There was a high correlation between the neurological insults' scale and the neurological symptom score in the IG and GG groups (r = .979 and .943 in the IG and GG groups, respectively). In animals with mild neurological symptom scores (2 and 3), the neuronal insults were significantly different between female and male gerbils in both IG and GG.

CONCLUSION

Our findings suggest that IG population would likely be more advantageous to establish an ischemic model.

A Patient-Specific Three-Dimensional Hemodynamic Model of the Circle of Willis

Circle of Willis (CoW) is one of the most important cerebral arteries in the human body and various attempts have been made to study the hemodynamic of blood flow in this vital part of the brain. In the present study, blood flow in a patient specific CoW is numerically modeled to predict disease-prone regions of the CoW. Medical images and computer aided design software are used to construct a realistic three-dimensional model of the CoW for this particular case. The arteries are considered as elastic conduits and the interactions between arterial walls and the blood flow are taken into account. Mooney-Rivlin hyperelastic model is used to describe the behavior of arterial walls and blood is considered as a non-Newtonian fluid obeying the Carreau model. An available experimental-based pulsatile velocity profile is used at the entrance of the CoW. The finite element-based commercial software, ADINA, is used to solve the governing equations. Blood pressure and velocity and arterial wall shear stress are calculated in different regions of the CoW. A simplified form of the model is also compared with the available published data. Results affirmed that the proposed computational model has the potential to capture the hemodynamic characteristics of the CoW. The computational results can be used to determine disease-prone locations for a given CoW.

Basilar Artery Diameter Is Inversely Associated with Fetal Type Circle of Willis

BACKGROUND

The relationship between basilar artery (BA) diameter and Circle of Willis (CoW) configuration has been scarcely investigated. We aimed to assess this association in community-dwelling older adults.

METHODS

MRAs of 346 individuals were reviewed. Using generalized linear models adjusted for demographics and cardiovascular risk factors, we assessed the relationship between BA diameter and fetal and non-fetal types CoW, as well as the impact of this relationship on BA ectasia prevalence.

RESULTS

In the total population, the mean BA diameter was 3.13 ± 0.68 mm and 7 subjects (2%) had ectasia (BA diameter >4.5 mm). In 248 subjects with non-fetal types CoW, the mean BA diameter was 3.32 ± 0.62 mm, and 2.8% had ectasia. In 98 subjects with fetal type CoW, the mean BA diameter was 2.66 ± 0.58 mm, and no individual had ectasia. The BA diameter was smaller in subjects with fetal type CoW than in those with non-fetal types (β 0.65; 95% CI 0.51-0.79; p < 0.001). Individuals with fetal type CoW have an 18% reduction in BA diameter compared to those with non-fetal types, independently of demographics and cardiovascular risk factors.

CONCLUSION

This study shows an inverse relationship between the BA diameter and the presence of fetal type CoW.

Completion of the Circle of Willis Varies by Gender, Age, and Indication for Computed Tomography Angiography

OBJECTIVE

The circle of Willis (CoW) is the foremost anastomosis and blood distribution center of the brain. Its effectiveness depends on its completion and the size and patency of its vessels. Gender-related and age-related anatomic variations in the CoW may play an important role in the pathogenesis of cerebrovascular diseases. In this study, we analyzed computed tomography angiograms (CTAs) to assess for differences in CoW completion related to gender, age, and indication for CTA.

METHODS

A total of 834 CTAs were retrospectively analyzed for all CoW vessels to compare the incidence of complete CoW and variation frequency based on gender, age, and indication.

RESULTS

The incidence of complete CoW was 37.1% overall. CoW completion showed a statistically significant decrease with increasing age for all age groups in both men (47.0%, 29.4%, 18.8%) and women (59.1%, 44.2%, 30.9%). Completion was greater in women (43.8%) than in men (31.2%) overall and for all age groups. These gender differences were all statistically significant except for the 18-39 years age group. The most frequent of the 28 CoW variations were absent posterior communicating artery (PCOM) bilaterally (17.1%), right PCOM (15.3%), and left PCOM (10.9%). Ischemic stroke and the 18-39 years age group of hemorrhagic stroke showed a statistically significant reduction in completion relative to trauma.

CONCLUSIONS

The incidence of complete CoW is likely greater in women for all age groups and likely decreases with age in both genders. The most frequently absent vessel is likely the PCOM, either unilaterally or bilaterally. Completion may play a role in ischemic stroke and a subset of patients with hemorrhagic stroke.

Tetralogy of Fallot Surgical Repair: Shunt Configurations, Ductus Arteriosus and the Circle of Willis

In this study, hemodynamic performance of three novel shunt configurations that are considered for the surgical repair of tetralogy of Fallot (TOF) disease are investigated in detail. Clinical experience suggests that the shunt location, connecting angle, and its diameter can influence the post-operative physiology and the neurodevelopment of the neonatal patient. An experimentally validated second order computational fluid dynamics (CFD) solver and a parametric neonatal diseased great artery model that incorporates the ductus arteriosus (DA) and the full patient-specific circle of Willis (CoW) are employed. Standard truncated resistance CFD boundary conditions are compared with the full cerebral arterial system, which resulted 21, -13, and 37% difference in flow rate at the brachiocephalic, left carotid, and subclavian arteries, respectively. Flow splits at the aortic arch and cerebral arteries are calculated and found to change with shunt configuration significantly for TOF disease. The central direct shunt (direct shunt) has pulmonary flow 5% higher than central oblique shunt (oblique shunt) and 23% higher than modified Blalock Taussig shunt (RPA shunt) while the DA is closed. Maximum wall shear stress (WSS) in the direct shunt configuration is 9 and 60% higher than that of the oblique and RPA shunts, respectively. Patent DA, significantly eliminated the pulmonary flow control function of the shunt repair. These results suggests that, due to the higher flow rates at the pulmonary arteries, the direct shunt, rather than the central oblique, or right pulmonary artery shunts could be preferred by the surgeon. This extended model introduced new hemodynamic performance indices for the cerebral circulation that can correlate with the post-operative neurodevelopment quality of the patient.

Analyzing Circle of Willis blood flow in ischemic stroke patients through 3D Stroke Arterial Flow Estimation

Background The objective of ischemic stroke (IS) treatment is to achieve revascularization in cerebral arteries to restore blood flow. However, there is no available method to extract arterial flow data from clinical CTA images. We developed 3D Stroke Arterial Flow Estimation (SAFE), which provides blood flow data throughout the Circle of Willis based on 3D CTA and allows comparison of arterial flow distribution in the brain. Methods We implemented a newly developed 3D vascular reconstruction algorithm for clinical stroke CTA images. Based on the patient-specific vascular structure, SAFE calculates time-resolved blood flow information for the entire Circle of Willis and allows quantitative flow study of IS cases. Clinical IS cases are presented to demonstrate the feasibility. Four patients with CTA images and CT perfusion data were studied. To validate the SAFE analysis, correlation analysis comparing blood flow at the MCA, ICA, and BA was performed. Results Different blood flow patterns were found in individual IS patients. Altered flow patterns and high collateral flow rates were found near occlusions in all cases. Quantitative comparison of blood flow data showed that SAFE obtained flow data and CTP were significantly correlated and provide complementary information about cerebral blood flow for individual patients. Conclusions We present SAFE analysis for collecting detailed time-resolved cerebral arterial flow data in the entire Circle of Willis for IS. Further study with more cases may be important to test the clinical utilization of SAFE and helpful to the study of the underlying hemodynamics of stroke.

Intracranial Blood Flow Changes in Patients with High-Grade Severe Carotid Artery Stenosis After Stenting

OBJECTIVE

We investigated whether the cerebral hemodynamic changes of pre- and poststenting in patients with severe carotid stenosis differ by stenosis grades.

METHODS

We prospectively recruited patients who underwent carotid artery stenting (CAS) after acute ischemic stroke from June 2014 to December 2015. We compared the mean relative cerebral blood flow (rCBF) changes (measured by whole-brain computed tomography perfusion) pre- and poststenting in patients with high-grade severe stenosis (HGSS) (90%-99%) versus patients with low-grade severe stenosis (LGSS) (70%-89%).

RESULTS

Among 24 patients included in the study (mean age, 66.2 ± 7.2 years; 91.7% men), 62.5% (15/24) were in the HGSS group and 37.5% (9/24) were in the LGSS group. In the HGSS group, rCBF increased in territories of the anterior cerebral artery (P = 0.021), middle cerebral artery (P < 0.001), posterior cerebral artery (P = 0.001), and basil ganglia (P = 0.003) after stenting. Of the patients with HGSS, 53.3% (8/15) had collateral flow through anterior communicating artery (AcomA) prestenting. After stenting, all the AcomA collaterals in HGSS reverted to normal (P = 0.002).

CONCLUSIONS

The improvement of brain perfusion combined with the normalization of collateral flow through the circle of Willis after CAS was observed only in patients with HGSS.

Importance of variants in cerebrovascular anatomy for potential retrograde embolization in cryptogenic stroke

OBJECTIVES

To test the hypothesis that variants in cerebrovascular anatomy will affect the number of patients demonstrating a plausible retrograde embolization mechanism from plaques in the descending aorta (DAo).

METHODS

Thirty-five patients (aged 63 ± 17 years) with cryptogenic stroke underwent 4D flow MRI for the assessment of aortic 3D blood flow and MR angiography for the evaluation of circle of Willis, posterior circulation, and aortic arch architecture. In patients with proven DAo plaque, retrograde embolization was considered a potential mechanism if retrograde flow extended from the DAo to a supra-aortic vessel supplying the cerebral infarct territory.

RESULTS

Retrograde embolization with matching cerebral infarct territory was detected in six (17%) patients. Circle of Willis and aortic arch variant anatomy was found in 60% of patients, leading to reclassification of retrograde embolization risk as present in three (9%) additional patients, for a total 26% of cryptogenic stroke patients.

CONCLUSION

4D flow MRI demonstrated 26% concordance with infarct location on imaging with retrograde diastolic flow into the feeding vessels of the affected cerebral area, identifying a potential etiology for cryptogenic stroke. Our findings further demonstrate the importance of cerebrovascular anatomy when determining concordance of retrograde flow pathways with vascular stroke territory from DAo plaques.

KEY POINTS

• Retrograde embolization from descending aortic plaques constitutes a plausible etiology in cryptogenic stroke. • Common variants of cerebrovascular anatomy are important in determining retrograde embolization mechanism. • Variant cerebrovascular anatomy can link retrograde flow pathways with vascular stroke territory.

Considerations on the Relevance of Cerebral Fusiform Aneurysms Observed During HIV Infection

Human immunodeficiency virus (HIV)-associated ectatic cerebral vasculitis (HIV-AECV) is a rare form of vasculitis with diffuse fusiform aneurysms. Its pathophysiology remains poorly understood. Although extensively described in children, it is still incompletely studied in adults. Our objective was to present five adult cases with emphasis on imaging findings and long-term evolution. From 2006 to 2014, we included 5 HIV-infected patients presenting with fusiform cerebral aneurysms. Vessels abnormalities were assessed with brain computed tomography (CT) angiography, magnetic resonance angiography (MRA) and/or digital subtraction angiography (DSA). All patients had MR assessment of the brain. Clinical and biological data were analyzed. Fusiform aneurysms of carotid terminations extending to middle and anterior cerebral arteries were bilateral in three patients and unilateral in one. More distal fusiform aneurysms were observed in four patients and saccular aneurysms in two patients, two patients suffered from ischemic lesions while none experienced hemorrhage. Unlike recent reviews, our study underlines the low hemorrhagic potential of HIV-AECV and long-term follow-up suggests a monophasic evolution under antiretroviral medication.

Non-Atherosclerotic Obliteration Of Bilateral Supraclinoid Internal Carotid Arteries; A Classic Case Of Moyamoya Disease

Moyamoya disease is an idiopathic progressive vasculopathy of distal internal carotid artery and circle of Willis which leads to the development of characteristic smoky appearance of the vascular collateral network on angiography. With the highest reported incidence among Japanese population, it has been under recognized as a cause of cerebrovascular accidents in Western countries. Here we report a case of a young 20-year-old Caucasian woman who presented to the emergency department with expressive aphasia, right arm weakness and numbness for three days. Imaging modalities confirmed Moyamoya disease.

Incomplete Circle of Willis: A risk factor for mesial temporal sclerosis?

OBJECTIVE

The aim of this study was to investigate whether there may be a correlation between the anatomical variants of Circle of Willis (CoW) and presence/laterality of mesial temporal sclerosis (MTS).

METHODS

We retrospectively identified the CoW variants on Wada angiograms in 71 patients with pathologically proven MTS. Angiograms were interpreted by two radiologists independently and blinded to clinical data. We divided the anterior and posterior components of the CoW into functionally complete and functionally incomplete groups. We then sought its correlation with the presence and laterality of MTS.

RESULTS

No statistically significant relationship was found between the functional status of the anterior circulation and the laterality of the MTS (p=0.657). Relationship of the posterior incomplete circle to MTS was statistically significant on both sides (p=0.023 for the left, p=0.04 for the right), with an effect size moderate to large for the left side and moderate for the right side. Although the fetal variant appeared to be related to the ipsilateral MTS, it did not reach to a level of statistical significance (p=0.15).

SIGNIFICANCE

The study demonstrates a statistically significant association of the incomplete posterior circulation of the CoW to the presence of ipsilateral MTS. Further studies in larger patient populations may be needed to seek whether an incomplete circulation may facilitate development of MTS, especially affecting the watershed zones.

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.

Electronic supplementary material

The online version of this article (doi:10.1186/s12880-016-0170-8) contains supplementary material, which is available to authorized users.

Atherosclerosis in the circle of Willis: Spatial differences in composition and in distribution of plaques

BACKGROUND AND AIMS

Intracranial atherosclerosis is one of the main causes of ischemic stroke. However, the characteristics of intracranial arteries and atherosclerosis have rarely been studied. Therefore, we systematically investigated atherosclerotic changes in all arteries of the Circle of Willis (CoW).

METHODS

Sixty-seven CoWs obtained at autopsy from randomly chosen hospital patients (mean age, 67.3 ± 12.5 years), of which a total of 1220 segments were collected from 22 sites. Atherosclerotic plaques were classified according to the revised American Heart Association classification and were related to local vessel characteristics, such as the presence of an external and internal elastic lamina and the elastic fibre density of the media.

RESULTS

181 out of the 1220 segments had advanced plaques (15%), which were mainly observed in large arteries such as the internal carotid, middle cerebral, basilar and vertebral artery. Only 11 out of 1220 segments (1%) showed complicated plaques (p < 0.001). Six of these were intraplaque hemorrhages (IPH) and observed only in patients who had cardiovascular-related events (p = 0.015). The frequency of characteristics such as the external elastic lamina and a high elastin fibre density in the media was most often associated with the vertebral artery. Only 3% (n = 33) of the CoW arteries contained calcification (p < 0.001), which were mostly observed in the vertebral artery (n = 13, 12%).

CONCLUSIONS

Advanced atherosclerotic plaques in the CoW are relatively scarce and mainly located in the 4 large arteries, and mostly characterized by an early and stable phenotype, a low calcific burden, and a low frequency of IPH.