Establishing the distribution of cerebrovascular resistance using computational fluid dynamics and 4D flow MRI.

Cerebrovascular resistance (CVR) regulates blood flow in the brain, but little is known about the vascular resistances of the individual cerebral territories. We present a method to calculate these resistances and investigate how CVR varies in the hemodynamically disturbed brain. We included 48 patients with stroke/TIA (29 with symptomatic carotid stenosis). By combining flow rate (4D flow MRI) and structural computed tomography angiography (CTA) data with computational fluid dynamics (CFD) we computed the perfusion pressures out from the circle of Willis, with which CVR of the MCA, ACA, and PCA territories was estimated. 56 controls were included for comparison of total CVR (tCVR). CVR were 33.8 ± 10.5, 59.0 ± 30.6, and 77.8 ± 21.3 mmHg s/ml for the MCA, ACA, and PCA territories. We found no differences in tCVR between patients, 9.3 ± 1.9 mmHg s/ml, and controls, 9.3 ± 2.0 mmHg s/ml (p = 0.88), nor in territorial CVR in the carotid stenosis patients between ipsilateral and contralateral hemispheres. Territorial resistance associated inversely to territorial brain volume (p < 0.001). These resistances may work as reference values when modelling blood flow in the circle of Willis, and the method can be used when there is need for subject-specific analysis.

The effect of circle of willis anatomy and scanning practices on outcomes for blunt cerebrovascular injuries.

BACKGROUND: Limited research has explored the effect of Circle of Willis (CoW) anatomy among blunt cerebrovascular injuries (BCVI) on outcomes. It remains unclear if current BCVI screening and scanning practices are sufficient in identification of concomitant COW anomalies and how they affect outcomes. METHODS: This retrospective cohort study included adult traumatic BCVIs at 17 level I-IV trauma centers (08/01/2017-07/31/2021). The objectives were to compare screening criteria, scanning practices, and outcomes among those with and without COW anomalies. RESULTS: Of 561 BCVIs, 65% were male and the median age was 48 y/o. 17% (n = 93) had a CoW anomaly. Compared to those with normal CoW anatomy, those with CoW anomalies had significantly higher rates of any strokes (10% vs. 4%, p = 0.04), ICHs (38% vs. 21%, p = 0.001), and clinically significant bleed (CSB) before antithrombotic initiation (14% vs. 3%, p < 0.0001), respectively. Compared to patients with a normal CoW, those with a CoW anomaly also had ischemic strokes more often after antithrombotic interruption (13% vs. 2%, p = 0.02).Patients with CoW anomalies were screened significantly more often because of some other head/neck indication not outlined in BCVI screening criteria than patients with normal CoW anatomy (27% vs. 18%, p = 0.04), respectively. Scans identifying CoW anomalies included both the head and neck significantly more often (53% vs. 29%, p = 0.0001) than scans identifying normal CoW anatomy, respectively. CONCLUSIONS: While previous studies suggested universal scanning for BCVI detection, this study found patients with BCVI and CoW anomalies had some other head/neck injury not identified as BCVI scanning criteria significantly more than patients with normal CoW which may suggest that BCVI screening across all patients with a head/neck injury may improve the simultaneous detection of CoW and BCVIs. When screening for BCVI, scans including both the head and neck are superior to a single region in detection of concomitant CoW anomalies. Worsened outcomes (strokes, ICH, and clinically significant bleeding before antithrombotic initiation) were observed for patients with CoW anomalies when compared to those with a normal CoW. Those with a CoW anomaly experienced strokes at a higher rate than patients with normal CoW anatomy specifically when antithrombotic therapy was interrupted. This emphasizes the need for stringent antithrombotic therapy regimens among patients with CoW anomalies and may suggest that patients CoW anomalies would benefit from more varying treatment, highlighting the need to include the CoW anatomy when scanning for BCVI. LEVEL OF EVIDENCE: Level III, Prognostic/Epidemiological.

Investigation of 3D vessel reconstruction under Doppler imaging with phantoms: Towards reconstruction of the Circle of Willis.

BACKGROUND: Stroke is the second leading cause of death across the globe. Early screening and risk detection could provide early intervention and possibly prevent its incidence. Imaging modalities, including 1D-Transcranial Doppler Ultrasound (1D-TCD) or Transcranial Color-code sonography (TCCS), could only provide low spatial resolution or 2D image information, respectively. Notably, 3D imaging modalities including CT have high radiation exposure, whereas MRI is expensive and cannot be adopted in patients with implanted devices. This study proposes an alternative imaging solution for reconstructing 3D Doppler ultrasound geared towards providing a screening tool for the 3D vessel structure of the brain. METHODS: The system comprises an ultrasound phased array attached to a servo motor, which can rotate 180˚ at a speed of 2˚/s. We extracted the color Doppler ROI from the image before reconstructing it into a 3D view using a customized pixel-based algorithm. Different vascular diameters, flow velocity, and depth were tested using a vascular phantom with a pumped flow to confirm the system for imaging blood flow. These variables were set to mimic the vessel diameter, flow speed, and depth of the Circle of Willis (CoW) during a transcranial screening. RESULTS AND CONCLUSIONS: The lower values of absolute error and ratio were found in the larger vascular channels, and vessel diameter overrepresentation was observed. Under different flow velocities, such diameter overrepresentation in the reconstructed flow did not change much; however, it did change with different depths. Meanwhile, the setting of the velocity scale and the color gain affected the dimension of reconstructed objectives. Moreover, we presented a 3D image of CoW from a subject to demonstrate its potential. The findings of this work can provide a good reference for further studies on the reconstruction of the CoW or other blood vessels using Doppler imaging.

Midterm follow-up after embolization of intracranial aneurysms proximal to the circle of Willis with the Silk Vista flow diverter: the I-MAMA registry.

PURPOSE: The aim of this registry was to assess technical success, procedural safety and mid- to long-term follow-up results of the Silk Vista "Mama" (SVM) flow diverter (BALT, Montmorency, France) for the treatment of proximal intracranial aneurysms. METHODS: Between August 2020 and March 2022, data from nine Italian neurovascular centres were collected. Data included patients' clinical presentation, aneurysms' size, location and status, technical details, overall complications and mid- to long-term angiographic follow-up. RESULTS: Forty-eight aneurysms in 48 patients were treated using the SVM. Most aneurysms were small (≤ 10 mm: no. 29, 60%) and unruptured (no. 31, 65%); 13 aneurysms were recurrent after coiling or clipping. 37/48 aneurysms involved the internal carotid artery (77%). Optimal opening and complete wall apposition of the device were achieved in 46 out of 48 cases (96%). Four intra- or periprocedural complications occurred (two thrombotic complications successfully resolved, one cerebellar ischemia, one perirenal hematoma), without new neurological deficit. No significant intra-stent stenosis or stent displacement was observed during follow-up. No FD-related morbidity nor mortality was reported. At midterm (6-12 months) to long-term (> 12 months) follow-up, complete aneurysm occlusion (OKM D) was achieved in 76% of cases. Eighty-eight percent of patients had complete aneurysm occlusion or entry remnant (OKM D + C). CONCLUSIONS: Our experience suggests that the new generation of low-profile SVM flow diverter for the treatment of proximal intracranial aneurysms is safe and effective, with low rates of intraprocedural complications and acceptable mid- to long-term occlusion rate.

Exploring the anatomical configurations of the cerebral arteries in a cohort of South African patients.

The cerebral arteries, specifically the anterior cerebral artery (ACA) and posterior cerebral artery (PCA), work together with the smaller calibre arteries to provide effective communication between the anterior and posterior circuits of the brain via the circle of Willis (CoW). Morphologic variations of the cerebral arteries and the CoW may alter blood flow to the brain, resulting in intracranial vascular disorders associated with stroke, and aneurysms. This study aimed to document the morphology of the cerebral arteries and the CoW in the South African population. Two hundred and thirty-nine computed tomography angiography scans were assessed. Cerebral arteries and CoW normal morphology and variations were classified as complete, absent, or hypoplastic. The ACA A1 was absent in 4.91%, hypoplastic in 30.40%, fenestrated in 1.06%, and typical in 63.6%. The ACA A2 was absent in 0.42%, hypoplastic in 26.28%, and typical in 69.44%. We found triple ACA A2 in 2.98%, azygos in 1.28% and fenestrated in 1.28%. The middle cerebral artery (MCA) was hypoplastic in 7.35% and typical in 92.64%. The PCA was hypoplastic in 28.74% and typical in 71.25%. Knowledge of the configuration of the CoW plays a significant role in guiding therapeutic decision-making in treating various neurovascular pathologies.

Development of the Circle of Willis Score (COWS) to help guide decision making during acute tandem occlusion treatment: Preliminary analysis.

BACKGROUND: Acute tandem occlusions (TOs) are challenging to treat. Although acute carotid stenting of the proximal lesion is well tolerated, there are certain situations when the practitioner may be wary of acute stenting (bleeding concerns). OBJECTIVE: The purpose of this study was to retrospectively study patients with tandem occlusions who had re-occlusion of the extracranial ICA and develop a Circle of Willis Score (COWS) to help predict which patients could forego acute stenting. METHODS: This is a retrospective review of TO patients with a persistent proximal occlusion following intervention (either expected or unexpected). Pre intervention CTA and intraoperative DSA were reviewed, and each patient was assigned a score 2 (complete COW), 1a (patent A1-Acomm-A1), 1p (patent Pcomm), or 0 (incomplete COW). Findings from the DSA took precedence over the CTA. Two cohorts were created, the complete COW cohort (COWS 2) versus the incomplete COW cohort (COWS 1a,1p, or 0). Angiographic outcomes were assessed using the mTICI score (2b-3) and clinical outcomes were assessed using discharge mRS (good outcome mRS 0-3). RESULTS: Of 68 TO cases, 12 had persistent proximal occlusions. There were 5/12 (42 %) patients in the complete COW cohort, and 7/12 (58 %) in the incomplete COW cohort (5/12 with scores of 1a/1p and 2/12 with a score of 0). In the complete COW cohort, there were 2 ICA-ICA and 3 ICA-MCA occlusions. In the incomplete COW cohort, there was one ICA-ICA occlusion and 6 ICA-MCA occlusions. LKW-puncture was shorter in the complete COW cohort (208 min vs. 464 min, p = 0.16). Successful reperfusion was higher in the complete COW cohort (100 % vs. 71 %). There was a trend toward better clinical outcomes in the complete COW cohort (80 % vs 29 %, p = 0.079). CONCLUSION: The COWS is a simple score that may help predict a successful clinical outcome without proximal revascularization when concerned about performing an acute carotid stent during TO treatment. Evaluation in larger TO cohort is warranted.

Anatomical differences of intracranial arteries according to sex: a systematic review and meta-analysis.

BACKGROUND AND PURPOSE: Intracranial aneurysms are more common in women than in men. Some anatomical variants of the circle of Willis (CoW) are associated with a higher risk of developing intracranial aneurysms. We hypothesized that variations of the CoW are sex dependent which may partly explain why intracranial aneurysms are more common in women. We systematically reviewed and meta-analyzed the literature to compare the presence of anatomical variations of the CoW between women and men in the general population. MATERIAL AND METHODS: A systematic search in Pubmed and EMBASE using predefined criteria, following the PRISMA guidelines was performed. The presence of different CoW anatomical variants and a complete CoW was compared between women and men using an inverse variance weighted random effects meta-analysis to calculate relative risks (RR) with 95% confidence intervals (95% CIs). RESULTS: Fourteen studies were included reporting on 5478 healthy participants (2511 women, 2967 men). Bilateral fetal type posterior cerebral arteries (RR 2.79; 95%CI 1.65-4.72, I2=0%), and a complete CoW (RR 1.24, 95%CI 1.13-1.36; I2=0%) were more prevalent in women than in men. The variants absence or hypoplasia of one of the anterior cerebral arteries (RR 0.58, 95%CI 0.38-0.88, I2=57%) and hypoplasia or absence of both posterior communicating arteries (RR 0.79, 95%CI 0.71-0.87, I2=0%) were more prevalent in men. CONCLUSIONS: Several anatomical variations of the CoW are sex dependent, with some variants being more common in women while others in men. Future research should assess how these sex-specific CoW variants relate to the sex-specific occurrence of intracranial aneurysms.

The Importance of the Circle of Willis in Carotid Interventions Outcomes: A Real-Life Study.

BACKGROUND: The main objective of this study is to evaluate and compare the outcomes regarding operative mortality rate, ipsilateral stroke, and overall survival rate among patients with internal carotid artery stenosis submitted to carotid endarterectomy (CEA) or stenting regarding the completeness of circle of Willis (CoW). METHODS: Prospective, consecutive cohort study of patients submitted to carotid interventions (CEA and carotid stenting: CAS) for internal carotid artery stenosis diagnosis evaluated according complete or incomplete CoW. The patients were divided into 2 groups: group I, the patients with complete CoW and group II, the patients with incomplete CoW, with the disruption of anterior and/or ipsilateral posterior circulation, regarding the ipsilateral significant carotid stenosis. RESULTS: Overall, 98 patients submitted to carotid intervention were evaluated. Two groups of patients were identified: group CoW complete with 54 patients and group CoW incomplete with 44 patients. Regarding the type of intervention, the prevalence of CAS in CoW complete group and CoW incomplete group were statistically similar (54.1% vs. 55.1%, P = 0.22). Notwithstanding, CEA was also statistically similar in CoW incomplete group and CoW complete group (44.2% vs. 45.9%, P = 0.22). The perioperative mortality rate was 2% in total cohort (2 patients), with no differences among CoW complete and incomplete groups (3.7% vs. 0%, P = 0.50, respectively). Furthermore, the incidence of postoperative stroke was 3.1% (asymptomatic 2%, symptomatic 1.1%), with no differences among CoW complete and incomplete groups (3.7% vs. 2.3%, P = 0.68, respectively). A univariate and multivariate linear regression showed that among the factors evaluated, only chronic kidney failure was related with hazard ratio = 1.89, P = 0.003, confidence interval 1.058-2.850. CONCLUSIONS: The completeness of the CoW, independently of the type of carotid intervention (CEA and CAS), did not interfere in the results regarding postoperative outcomes for stroke and death. Chronic kidney disease was associated to increased risk of perioperative stroke.

Hemorragia Intracerebral Imprevisible en un Hombre Joven: La Importancia de la Tomografía computarizada craneal post-mortem / Unpredictable Intracerebral Hemorrhage in a Young Male: The Importance of Post-Mortem Cranial Computed Tomography

La muerte súbita es aquella que ocurre dentro de las 24 horas posteriores al inicio de los síntomas y se caracteriza por ser clínicamente inexplicable, inesperada y repentina. Debido a la naturaleza de la muerte súbita, no es posible llegar a un diagnóstico preciso sin una autopsia. En esta comunicación breve, evaluaremos el caso de un empleado de crucero de 33 años, sin historial médico/farmacológico previo, el cual falleció súbitamente mientras reposaba en su camarote. Debido a las sospechas iniciales de una posible muerte causada por una sobredosis de cocaína, se le realizó un panel toxicológico abarcador el cual resultó negativo. Empero, una tomografía computarizada (TC) craneal sin contraste revirtió la hipótesis inicial y la autopsia neuropatológica -sorpresivamente- confirmó que la verdadera causa de muerte fue la ruptura de un aneurisma sacular desconocido en el polígono de Willis.

Sudden death occurs within 24 hours after the onset of symptoms and is characterized by being clinically inexplicable, sudden, and unexpected. Due to the nature of sudden death, it is not possible an accurate diagnosis without performing an autopsy. In this brief communication, we will evaluate the case of a 33-year-old cruise employee, with no prior medical/pharmacological history, who suddenly died while resting in his cabin. Due to initial suspicions of a possible cocaine overdose death, a comprehensive toxicology panel was performed, although yielding a negative result. A cranial computed tomography without contrast reversed the initial hypothesis and the neuropathological autopsy -surprisingly- confirmed that the true cause of death was the rupture of an unknown saccular aneurysm in the Circle of Willis.

Comparison of bone subtraction CT angiography with standard CT angiography for evaluating circle of Willis in normal dogs.

BACKGROUND: Bone subtraction computed tomography angiography (BSCTA) is a useful alternative technique for improving visualization of vessels surrounded by skull bone. However, no studies have compared computed tomography angiography (CTA) and BSCTA for improving the visibility of canine cerebral blood vessels. OBJECTIVES: To evaluate the potential benefit of BSCTA for better delineation of brain arteries of the circle of Willis (CoW) in dogs by comparing BSCTA with non-subtraction computed tomography angiography (NSCTA). METHODS: Brain CTA was performed for nine healthy beagle dogs using a bolus tracking method with saline flushing. A total dose of 600 mgI/kg of contrast agent with an iodine content of 370 mgI/mL was injected at a rate of 4 ml/s. Bone removal was achieved automatically by subtracting non-enhanced computed tomography (CT) data from contrast CT data. Five main intracranial arteries of the CoW were analyzed and graded on a scale of five for qualitative evaluation. RESULTS: Scores of basilar artery, middle cerebral artery, and rostral cerebral artery in the BSCTA group were significantly higher than those in the NSCTA group (p = 0.001, p = 0.020, and p < 0.0001, respectively). Scores of rostral cerebellar artery (RcA) and caudal cerebral artery (CCA) did not differ significantly between the two groups. However, scores of RcA and CCA in the BSCTA group were higher than those in the NSCTA group. CONCLUSIONS: BSCTA improved visualization of intracranial arteries of the CoW with close contact to bone. Thus, it should be recommended as a routine scan method in dogs suspected of having brain vessel disease.

Using deep learning for an automatic detection and classification of the vascular bifurcations along the Circle of Willis.

Most of the intracranial aneurysms (ICA) occur on a specific portion of the cerebral vascular tree named the Circle of Willis (CoW). More particularly, they mainly arise onto fifteen of the major arterial bifurcations constituting this circular structure. Hence, for an efficient and timely diagnosis it is critical to develop some methods being able to accurately recognize each Bifurcation of Interest (BoI). Indeed, an automatic extraction of the bifurcations presenting the higher risk of developing an ICA would offer the neuroradiologists a quick glance at the most alarming areas. Due to the recent efforts on Artificial Intelligence, Deep Learning turned out to be the best performing technology for many pattern recognition tasks. Moreover, various methods have been particularly designed for medical image analysis purposes. This study intends to assist the neuroradiologists to promptly locate any bifurcation presenting a high risk of ICA occurrence. It can be seen as a Computer Aided Diagnosis scheme, where the Artificial Intelligence facilitates the access to the regions of interest within the MRI. In this work, we propose a method for a fully automatic detection and recognition of the bifurcations of interest forming the Circle of Willis. Several neural networks architectures have been tested, and we thoroughly evaluate the bifurcation recognition rate.

Incompleteness of the Circle of Willis and progression of white matter hyperintensities of presumed vascular origin. A longitudinal prospective study in community-dwelling older adults.

BACKGROUND: Evidence on the association between anatomical variants of the circle of Willis (CoW) and severity of white matter hyperintensities (WMH) of presumed vascular origin is inconclusive, and no study has evaluated the role of incompleteness of CoW on WMH progression in the follow-up. This study aims to assess the impact of incomplete configurations of the CoW on WMH progression in community-dwelling older adults. METHODS: Following a prospective longitudinal study design, individuals aged ≥60 years enrolled in the Atahualpa Project Cohort from 2012 to 2019 were invited to receive baseline brain MRI and MRA of intracranial vessels, and those who also had brain MRIs at the end of the study (May 2021) were included in the analysis. Poisson regression models, adjusted for demographics and cardiovascular risk factors, were fitted to assess the incidence rate ratio (IRR) of WMH progression according to incompleteness of CoW. RESULTS: This study included 254 individuals (mean age: 65.4±5.9 years; 55% women). An incomplete CoW was detected in 99 (39%) subjects. Follow-up MRIs showed WMH progression in 103 (41%) individuals after a median follow-up of 6.5±1.4 years. WMH progression was observed in 58/155 subjects with complete and in 45/99 with incomplete CoW (37% versus 45%; p=0.203). There was no association between incomplete CoW and WMH progression in a multivariate Poisson regression model (IRR: 1.21; 95% C.I.: 0.81 - 1.82). CONCLUSIONS: Study results show that incompleteness of CoW is not involved in WMH progression.

Anatomical variations in the circle of Willis are associated with increased odds of intracranial aneurysms: The Tromsø study.

PURPOSE: Studies on patients suggest an association between anatomical variations in the Circle of Willis (CoW) and intracranial aneurysms (IA), but it is unclear whether this association is present in the general population. In this cross-sectional population study, we investigated the associations between CoW anatomical variations and IA. METHODS: We included 1667 participants from a population sample with 3 T MRI time-of-flight angiography (40-84 years, 46.5% men). Saccular IAs were defined as protrusions in the intracranial arteries ≥2 mm, while variants of the CoW were classified according to whether segments were missing or hypoplastic (< 1 mm). We used logistic regression, adjusting for age and IA risk factors, to assess whether participants with incomplete CoW variants had a greater prevalence of IA and whether participants with specific incomplete variants had a greater prevalence of IA. RESULTS: Participants with an incomplete CoW had an increased prevalence of IA (OR, 2.3 [95% CI 1.05-5.04]). This was mainly driven by the variant missing all three communicating arteries (OR, 4.2 [95% CI 1.7-1 0.3]) and the variant missing the P1 segment of the posterior cerebral artery (OR, 3.6 [95% CI 1.2-10.1]). The combined prevalence of the two variants was 15.4% but accounted for 28% of the IAs. CONCLUSION: The findings suggest that an incomplete CoW is associated with an increased risk of IA for adults in the general population.

Influence of the integrity of circle of Willis on asymptomatic or mild patients with first diagnosed chronic internal carotid artery occlusion.

BACKGROUND: In order to identify individuals with chronic internal carotid artery occlusion (CICAO), it is essential to understand the integrity of the circle of Willis (CoW). This understanding is important as it may determine the potential benefits of active medical and endovascular treatments. PURPOSE: The objective of this study is to assess whether diminished integrity of the CoW can serve as a useful marker for identifying individuals with more severe impairment in cerebral blood perfusion and a higher incidence of cerebral infarction among asymptomatic or mildly affected patients with CICAO. MATERIALS AND METHODS: We conducted a retrospective review of asymptomatic or mildly affected patients with newly diagnosed CICAO who did not receive reperfusion therapies. The categorization of patients into good or poor integrity groups was based on the assessment of CoW integrity using CTA. We evaluated the volume and value of prolonged time to peak (TTP) in both groups, as well as the occurrence of new cerebral infarctions. Our analysis involved multivariate regression and receiver operating characteristic (ROC) analysis. RESULTS: Hemodynamic abnormalities characterized by prolonged TTP were observed in the affected side's blood supply region in all 38 patients. There was a notable difference in the volume and value of prolonged TTP between the two groups (P < 0.001). Correlation analyses based on CTP and CTA parameters revealed a negative relationship between CoW scores and both the abnormal volume (r = -0.624, P = 0.000) and value (r = -0.589, P = 0.000) of prolonged TTP. Upon multivariable adjustment, the independent predictors for new cerebral infarction and higher volume of prolonged TTP were solely the CoW status, with respective estimates of (b = 6.05; 95% confidence interval [CI]: 1.619, 22.619; P = 0.007) and (b = 35.486; 95% CI: 4.697, 268.088; P = 0.001). CONCLUSION: Assessing the integrity of the CoW is crucial in evaluating abnormal perfusion in asymptomatic or mildly affected individuals who are newly diagnosed with CICAO and have not undergone reperfusion therapy.

False Absence of the Anterior Communicating Artery and a Median Artery of Corpus Callosum.

The anterior communicating artery (AComA) normally joins the anterior cerebral arteries (ACAs) when they change their directions from horizontal to vertical. Each postcommunicating segment of the ACAs commonly sends off the callosomarginal artery (CMA) and continues as the pericallosal artery. While documenting the archived computed tomography angiogram of a 61-year-old male patient, a rare anatomic variant was found to be associated with a previously unreported one. Both ACAs had symmetrical horizontal and vertical segments, but the AComA was absent from the usual location. The right ACA continued as CMA without sending off a pericallosal artery. A median artery of corpus callosum (MACC) left from the horizontal segment of the left ACA. Then the left ACA continued as CMA. At 1.9 cm from its origin, the MACC was united to the right CMA by a high, interhemispheric AComA. Therefore, an AComA should be regarded as absent only after documenting the bilateral anastomoses within the interhemispheric fissure. A third interhemispheric main artery, such as a rarely occurring MACC, could be accurately documented by computed tomography angiogram to avoid unpleasant intraoperative hemorrhage or to establish a personalized endovascular route to the anterior cerebral system.

The Venous Circle of Trolard: An Anatomical Study with Application to Approaches to the Basal Brain.

BACKGROUND: The arterial circle of Willis is a well-known and interconnecting set of blood vessels at the base of the brain. However, its lesser-known venous counterpart, the circle of Trolard, has had almost no attention in the extant medical literature. METHODS: Twenty-four adult human brains underwent dissection of the circle of Trolard. When identified, its component vessels and relationships with adjacent structures were confirmed and documented with photography and measured using microcalipers. RESULTS: A complete circle of Trolard was identified on 42% of specimens. Most (64%) incomplete circles were incomplete anteriorly with no anterior communicating vein. The anterior communicating veins joined the anterior cerebral veins superior to the optic chiasm and continued posteriorly. The anterior communicating veins had a mean diameter of 0.45 mm. The length of these veins ranged from 0.8 mm to 1.45 mm. Thirty-six percent of circles were incomplete posteriorly with lack of a posterior communicating vein. The posterior communicating veins were always larger and longer than the anterior cerebral veins. The posterior communicating veins had a mean diameter of 0.8 mm. The length of these veins ranged from 2.8 to 3.9 cm. In general, the circles of Trolard were more or less symmetrical. However, in 2 specimens, asymmetry existed. CONCLUSIONS: A better understanding of the venous circle of Trolard might decrease iatrogenic injury during approaches to the base of the brain and improve diagnoses based on imaging of the skull base. To our knowledge, this is the first anatomical study dedicated to the circle of Trolard.

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

BACKGROUND: The main scope of this paper is to investigate the prevalence of the anatomical variants of the circle of Willis (CoW) in the Romanian population through magnetic resonance angiography. MATERIALS AND METHODS: Magnetic resonance angiography images were obtained for 126 individuals and the configurations of the anterior and posterior CoW were identified, and classified. The prevalence of each variant and the number of complete anterior or posterior parts of the circle were determined. RESULTS: A classical configuration of the CoW was found in 39 (30.9%) cases. The most common posterior variation was the unilateral absence of a posterior communicating artery (n = 28) while in the anterior circle it was the unilateral absence of the precommunicating segment of an anterior cerebral artery (n = 17). A complete entire CoW was found in 63 cases, while the anterior and posterior parts yielded complete configurations in 108 and 73 cases, respectively. Eight cases did not present complete configurations. A foetal posterior communicating artery was identified unilaterally in 14 cases and bilaterally in 6 cases. CONCLUSIONS: Unilateral variations were the most common changes found in CoW configuration. The correct assessment of the CoW configuration may prove useful in the planning and follow-up of brain surgery and interventional procedures, as well as in estimating the prognosis of patients suffering from stroke or other related cerebral vascular events.

Flow control in the middle cerebral artery during thrombectomy: the effect of anatomy, catheter size and tip location.

BACKGROUND: Catheter size, location and circle of Willis anatomy impact the flow conditions during interventional stroke therapy. The aim of the study was to systematically investigate the influence of these factors on flow control in the middle cerebral artery by means of a computational model based on 100 patients with stroke who received endovascular treatment. METHODS: The dimensions of the cervical and intracranial cerebral arteries of 100 patients who received endovascular mechanical thrombectomy for acute ischemic stroke were measured and a three-dimensional model of the circle of Willis was created based on these data. Flow control in the middle cerebral artery with variations in catheter size, catheter location and configurations of collateral vessels was determined using a computational model. A total of 48 scenarios were analyzed. RESULTS: Flow reversal with a distal aspiration catheter alone was not possible in the internal carotid artery and only sometimes possible in the middle cerebral artery (14 of 48 cases). The Catalyst 7 catheter was more often successful in achieving flow reversal than Catalyst 5 or 6 catheters (p<0.001). In a full circle of Willis anatomy, flow reversal was almost never possible. The absence of one or more communicating arteries significantly influenced flow direction compared with the full anatomy with all communicating arteries present (p=0.028). CONCLUSION: Choosing the biggest possible aspiration catheter and locating it in the middle cerebral artery significantly increases the chances of successful flow control. Flow through the collaterals may impair the flow, and circle of Willis anatomy should be considered during aspiration thrombectomy.

Effects of abnormal vertebral arteries and the circle of Willis on vertebrobasilar dolichoectasia: A multi-scale simulation study.

BACKGROUND: Vertebrobasilar dolichoectasia is a rare cerebrovascular disease characterized by obvious extension, dilation and tortuosity of vertebrobasilar artery, and its pathophysiological mechanism is not clear. This study focused on local hemodynamic changes in basilar arteries with typical vertebrobasilar dolichoectasia, together with unbalanced vertebral arteries and abnormal structures of the circle of Willis, through multi-scale modeling. METHODS: Three-dimensional models of 3 types of vertebrobasilar arteries were constructed from magnetic resonance images. The first type has no vertebrobasilar dolichoectasia, the second type has vertebrobasilar dolichoectasia and balanced vertebral arteries, and the third type has vertebrobasilar dolichoectasia and unbalanced vertebral arteries. A lumped parameter model of the circle of Willis was established and coupled to these three-dimensional models. FINDINGS: The results showed that unbalanced bilateral vertebral arteries, especially single vertebral artery deletion mutation, might associate with higher wall shear stress on anterior wall of basilar artery in patients with vertebrobasilar dolichoectasia. And unbalanced bilateral vertebral arteries would increase the blood pressure in basilar artery. Meanwhile, missing communicating arteries in the circle of Willis, especially bilateral posterior communicating arteries absences, would significantly increase blood pressure in basilar artery. The unilateral absence of posterior communicating arteries would increase differences in blood flow between the left and right posterior cerebral arteries. INTERPRETATION: This study provided a multi-scale modeling method and some preliminary results for helping understand the role of hemodynamics in occurrence and development of vertebrobasilar dolichoectasia.