Clinical applicability of a mathematical model in assessing the functional ability of the communicating arteries of the circle of Willis

Pre-operative transcranial Doppler ultrasound assessment of cerebral collateral circulation in children undergoing veno-arterial extracorporeal membrane oxygenation or cardiac surgery

Children requiring veno-arterial extracorporeal membrane oxygenation (VA ECMO) or cardiac surgery often undergo cervical cannulation or carotid artery clamping, which can interrupt cerebral circulation. Inadequate collateral flow through the circle of Willis (CoW) may lead to cerebral ischaemia within the vascular territory and/or watershed regions. Pre-cannulation survey of the CoW using transcranial Doppler (TCD) ultrasound may be performed to predict and plan neuroprotection. It is important to note in this article TCD refers to Duplex or colour coded trans-cranial Doppler (TCCD) using radiology-based machines, which is distinct from the more traditional trans-cranial Doppler technique that does not incorporate a B-mode image. This article describes our technique, in use since 2019, to guide surgical approaches and neuroprotective measures when an incomplete CoW is identified. High-end radiology-based ultrasound platforms and various transducers are used to assess brain morphology and haemorrhage through the anterior fontanelle in neonates. TCD is performed with the highest frequency transducer possible, utilising Doppler imaging to visualise cerebral arteries. Manual carotid compression can be used to functionally assess collateral flow when segments appear aplastic or hypoplastic. Potential pitfalls include mistaking the anterior choroidal artery for a hypoplastic posterior communicating artery (PCommA). Since implementing this protocol 5 years ago, no catastrophic infarcts related to cervical cannulation have occurred. This technique provides a practical solution for pre-operative assessment of cerebral collateral circulation in children undergoing VA ECMO or cardiac surgery, allowing for consideration of neuroprotective measures and improving patient safety.

Human cerebral blood supply via circulus arteriosus cerebri: A scoping review on its variations and clinical implications

Background

Circulus arteriosus cerebri (CAC), responsible for supplying blood to the brain, presents anatomical variations that have been associated with both haemorrhagic and ischemic strokes. Therefore, it is crucial to conduct comprehensive investigations and comparisons of the diverse variant components of the CAC, published in various journals, and analyze them to identify individuals at risk of cerebrovascular pathologies, thereby ensuring enhanced and timely treatment.

Methods

A scoping review according to the five-stage protocol by Arksey and O'Malley was performed between February and June 2023. Seven hundred and seventy-seven records were initially identified, and a total of 51 studies were finally included.

Results

This scoping review focuses on the anatomical variations of the CAC and their clinical implications on cerebrovascular disease and includes more original articles than review s. Consistent with previous findings, most of the records included small populations or samples, while only three records reported larger populations. Surprisingly, the populations enclosed in the included records consisted of autopsied cadaveric specimens more than living subjects. Finally, the qualitative analysis highlighted three main themes concerning the relationship between the normal CAC morphology and the cerebrovascular disease onset as well as the variant CAC morphology and its main features that might be also involved in these diseases. Finally, techniques that can be used to measure CAC have also been assessed.

Conclusion

Variations in the CAC, more common in the posterior part, with genetic and environmental factors influencing these variations impact cerebrovascular disorders. Understanding variants components of CAC can aid in improving brain surgeries and post-stroke care.

Incomplete circle of Willis as a risk factor for intraoperative ischemic events during carotid endarterectomies performed under regional anesthesia - A prospective case-series

Background

The role of the willisian collaterals during carotid endarterectomies (CEAs) is a debated issue. The aim of the present work was to test whether an incomplete or non-functional circle of Willis (CoW) is a risk factor for ischemic events during CEA.

Patients and methods

CEAs were performed under local anesthesia. Patients were considered symptomatic (SY) if neurological signs appeared after the cross-clamping phase. In SY patients shunt insertion was performed. CoW on CT angiograms (CTa) were analyzed offline and categorized as non-functional (missing or hypoplastic collaterals) or functional collaterals by three neuroradiologists. Near-infrared spectroscopy (NIRS) was performed throughout the procedure.

Results

Based on CTa, 67 incomplete circles were found, 54 were asymptomatic (ASY) and 13 were SY. No complete CoW was found among the SY patients. Significant differences could be detected between incomplete and complete circles between ASY and SY groups (Chi-square: 6.08; p = 0.013). The anterior communicating artery was missing or hypoplastic in 5/13 SY cases. There were no cases of the non-functional anterior communicating arteries in the ASY group (Chi-square: 32.9; p = 10^-8). A missing or non-functional bilateral posterior communicating artery was observed in 9/13 SY and in 9/81 ASY patients (Chi-square: 24.4; p = 10^-7). NIRS had a sensitivity of 76.9% and a specificity of 74.5% in detecting neurological symptoms.

Conclusions

Collateral ability of the CoW may be a risk factor for ischemic events during CEAs. Further studies should delineate whether the preoperative assessment of collateral capacity may be useful in decision-making about shunt use during CEA.

Combination of High-Density Lipoprotein Cholesterol and Lipoprotein(a) as a Predictor of Collateral Circulation in Patients With Severe Unilateral Internal Carotid Artery Stenosis or Occlusion

BACKGROUND AND PURPOSE

Collateral circulation is considered an important factor affecting the risk of stroke, but the factors that affect collateral circulation remain unclear. This study was performed to identify the factors associated with collateral circulation, especially blood lipids.

METHODS

The study involved patients who had undergone digital subtraction angiography and were confirmed as having severe unilateral stenosis or occlusion of the internal carotid artery (ICA). We classified the collateral circulation status of each patient as good (Grade 3 or 4) or poor (Grade 0, 1, or 2) according to the grading system of the American Society of Interventional and Therapeutic Neuroradiology/American Society of Interventional Radiology. We collected data on patients' characteristics and identified the factors that affect collateral circulation.

RESULTS

This study included 212 patients. The multivariate logistic regression analysis showed that the high-density lipoprotein cholesterol (HDL-C) concentration and a complete anterior half of the circle of Willis were independent protective factors for good collateral circulation, whereas elevated lipoprotein(a) [Lp(a)] and serum creatinine concentrations were independent risk factors for good collateral circulation. The area under the receiver operating characteristics curve (AUC) was 0.68 (95% confidence interval [CI], 0.61-0.76) for HDL-C and 0.69 (95% CI, 0.62-0.76) for Lp(a). A binary logistic regression model analysis of the joint factor of HDL-C and Lp(a) yielded an AUC of 0.77 (95% CI, 0.71-0.84).

CONCLUSIONS

In patients with severe unilateral ICA stenosis or occlusion, the combination of HDL-C and Lp(a) is a useful predictor of collateral circulation.

Assessment of malformations, variations and diameters of vessels forming the circle of Willis - An autopsy study in a non-cerebrovascular cohort

BACKGROUND A PURPOSE

The collateral capacity of the circle of Willis (CoW) may play an important role in the development of ischemic strokes. The occurrence of classical polygon shows wide geographical variations and morphological data on diameters of the Willisian collaterals are scarce. We aimed to assess CoW variations and vessel diameters in a Central European cohort.

SUBJECTS AND METHODS

CoWs were removed during routine autopsy. The morphological pattern of the circles was recorded. The prepared circles were then put between two glass plates and tightly compressed. The length of the vessels and half of the circumference were measured under a light microscope enabling measurement with an approximation of 0.1 mm. Vessel diameters were calculated from vessel circumference.

RESULTS

A total of 110 circles were analysed. Incomplete circles (missing one or two segments of CoW) were found in 25 cases (22.7%). Any forms of anatomical variations were detected in 14 cases (12.7%). When applying the <1 mm diameter threshold for analysis, 36 anterior communicating arteries (32.7%), 53 right posterior communicating arteries (48.2%), 73 left posterior communicating arteries (66.4%) and 18 posterior communicating arteries (16.3%) on both the sides were considered hypoplastic.

CONCLUSIONS

In patients without stroke in their history, complete CoW may be present in >60% of the cases. Our diameter data may serve as reference values for the Central-European population.

Leptomeningeal collateral flow in patients with middle cerebral artery occlusion assessed by transcranial Doppler

BACKGROUND AND PURPOSE

To explore the application value and clinical significance of transcranial Doppler(TCD)in assessing leptomeningeal collateral flow (LMF) status in patients with unilateral middle cerebral artery (MCA) occlusion.

METHODS

Medical records of patients with unilateral MCA occlusion confirmed by digital subtraction angiography (DSA) were analyzed retrospectively. The patients were divided into three groups according to LMF status, and the laboratory and imaging results were collected. Cerebral blood flow velocity (CBFV) of MCA, anterior cerebral artery (ACA), and posterior cerebral artery (PCA) on the affected side (ipsilateral, i) and the healthy side (contralateral, c) were measured and recorded by TCD. The results of CBFV changes detected by TCD were compared with those of DSA, and the correlation between CBFV changes and LMF status was analyzed.

RESULTS

Eighty-four patients with unilateral MCA occlusion were included. CBFViACA and CBFViPCA were significantly faster than CBFVcACA and CBFVcPCA in patients with good LMF status (p<.05). There was a significant positive correlation between CBFViACA and LMF status (r = 0.697, p<.001). There was statistical significance in receiver operating characteristic curve analysis of CBFViACA and CBFViPCA (p<.05). The area under the curve of CBFViACA and CBFViPCA, respectively, was 0.879 and 0.678, and the best cutoff value was 82 and 60.5 cm/s.

CONCLUSIONS

TCD can assess LMF status by detecting the changes of flow velocity of intracranial vessels. CBFV of ACA and PCA in patients with MCA occlusion is significantly correlated with LMF status by DSA. Assessing LMF status, CBFViACA, CBFViACA/CBFVcACA, and CBFViACA/CBFViMCA has the great diagnostic value, which is of great significance in guiding MCA occlusion patients to choose individualized treatment.

Collateral flow at circle of Willis in healthy condition

Experimental simulation of cerebrovascular system would be very beneficial tool to evaluate millions of human body cascade sequence. The Circle of Willis (CoW) recently named Cerebral Arterial Circle (CAC) is a main loop structure of cerebral circulatory system which positioned at the cranium base. In this research, we investigate cerebral artery flow pattern in cerebral arteries including afferent, Willisian, and efferent arteries of CAC emphasizing on communicating and connecting arteries which are main routes in CAC and as a risky sites when autoregulation is occurred in terminal parts of middle cerebral arteries (MCAs) by PMMA (Polymethyl methacrylate) chip and high quality camera which depict Sequential images. This novelty study analyze flow pattern in CAC that have been challenging subject area for many years which have investigated by scientists yet, because flow pattern in CAC indicate complication progression. This research tries to construct new platform in cerebral circulation analyzing method by reliable experimental in-vitro approach. The outcomes of this study demonstrate that communicating arteries especially anterior communicating artery (ACoA) is main artery in CAC flow distribution.

Is Anatomical Variations a Risk Factor for Cerebral Vasospasm in Anterior Communicating Complex Aneurysms Rupture?

Background and Purpose- One-third of ruptured aneurysms are located on the anterior communicating complex with high prevalence of anatomic variations of this arterial segment. In this study, we hypothesized that anatomic variations of the anterior communicating complex increase the risk of angiographic vasospasm. Methods- Retrospective study of prospectively collected data from a monocentric subarachnoid hemorrhage cohort of patients admitted to neurointensive care between 2002 and 2018. Univariate followed by multivariate logistic regression analysis was used to identify factors associated with angiographic vasospasm. Results- One thousand three hundred seventy-four patients with aneurismal subarachnoid hemorrhage were admitted to our institution; 29.8% (n=410) were related to an anterior communicating complex aneurysm rupture; 9.2% (n=38) of them showed an anterior communicating artery variation. Angiographic vasospasm was diagnosed in 55.6% of this subgroup (vs 28.1%, P=0.003). In the multivariate analysis, external ventricular drain (2.2 [1.32-3.65], P=0.003) and anterior communicating artery variation (2.40 [1.2-4.9], P=0.04) were independently and significantly associated with angiographic vasospasm, while age above 60 years (0.3 [0.2-0.7]; P=0.002) was a protective factor. However, anterior communicating artery variation was not statistically associated with ischemic vasospasm or poor neurological outcome after anterior communicating artery aneurysm rupture. Conclusions- Anatomic variation of anterior communicating artery could be a new biomarker to identify patients at risk to develop angiographic vasospasm post-subarachnoid hemorrhage. External validation cohorts are necessary to confirm these results.

Functional posterior communicating artery of patients with posterior circulation ischemia using phase contrast magnetic resonance angiography

Posterior communicating artery (PCoA) in patients with posterior circulation ischemia (PCI) was quantitatively studied using phase contrast magnetic resonance angiography (PC-MRA). Fifty-one cases who received PC-MRA were included in the study, and divided into the research and control groups. The mean flow volume, mean flow velocity, minimum flow volume, maximum flow volume, minimum flow velocity and maximum flow velocity of the basal artery (BA), bilateral vertebral arteries, internal carotid arteries and functional posterior communicating artery (F-PCoA) were recorded, the peak heights of flow volume and flow velocity were calculated, and the typing of F-PCoA was analyzed, followed by statistical analysis. Fifty-two F-PCoAs were detected, and the median values of mean flow volume, mean flow velocity, cross-sectional area and lumen diameter were 20.31 ml/min, 4.01 cm/sec, 0.08 cm² and 0.16 cm, respectively. The blood flow curve of F-PCoA showed the sawtooth-like changes, and there could be either unidirectional blood flow or bidirectional blood flow in one cardiac cycle. F-PCoA was divided into the following 3 types: F-PCoA was consistent with anatomical PCoA (A-PCoA), F-PCoA was inconsistent with A-PCoA, and mixed type. In the presence of F-PCoA, both the diameter and cross-sectional area of BA were small, and the maximum flow velocity and peak height of flow volume were reduced, but there was no necessary correlation with the occurrence of PCI. Both flow volume and flow velocity of BA in the research group were reduced, and the forward posterior shunt flow of F-PCoA was increased. Hemodynamic characteristics of F-PCoA can be analyzed via PC-MRA. The forward posterior shunt flow of F-PCoA can provide references for the clinical auxiliary diagnosis.

Hemodynamics in the Circle of Willis with Internal Carotid Artery Stenosis under Cervical Rotatory Manipulation: A Finite Element Analysis

Background

The circle of Willis (CoW) plays an important role in cerebral collateral circulation. The hemodynamics changes in the CoW have usually been associated with the internal carotid artery (ICA) stenosis, but whether rotatory manipulation will affect it remains unknown.

Material/Methods

In this study we attempted to analyze the influence of rotatory manipulation on the hemodynamics in the CoW in models with or without ICA stenosis by means of finite element analysis. For this purpose, the CoW was reasonably simplified and a fluid-solid coupling 3D finite element model was created by using MIMICS10.0 and ANSYS14.5. The healthy (without stenosis) and the diseased (ratios of stenosis include 15%, 30%, 45%, 60%, 70%, 80%, and 90%) situations were simulated. A remote displacement of 60° was applied at a distal ICA (the right ICA was chosen here) to imitate the rotatory manipulation. Blood flow was then monitored at the anterior communicating artery (ACoA) and posterior communicating arteries (PCoA).

Results

Before the conduction of rotatory manipulation, blood flow changed significantly only when the stenosis ratio was increased to more than 70%, and the situation did not have significant difference after the application of remote displacement except the model with stenosis ration of 90%.

Conclusions

The result suggests that the rotatory manipulation does not have an obvious influence on the blood flow in the CoW when the stenosis of ICA is less than 90%, and this kind of manipulation is suggested to be a safe technique in most of the clinical applications.

Function of circle of Willis

Nearly 400 years ago, Thomas Willis described the arterial ring at the base of the brain (the circle of Willis, CW) and recognized it as a compensatory system in the case of arterial occlusion. This theory is still accepted. We present several arguments that via negativa should discard the compensatory theory. (1) Current theory is anthropocentric; it ignores other species and their analog structures. (2) Arterial pathologies are diseases of old age, appearing after gene propagation. (3) According to the current theory, evolution has foresight. (4) Its commonness among animals indicates that it is probably a convergent evolutionary structure. (5) It was observed that communicating arteries are too small for effective blood flow, and (6) missing or hypoplastic in the majority of the population. We infer that CW, under physiologic conditions, serves as a passive pressure dissipating system; without considerable blood flow, pressure is transferred from the high to low pressure end, the latter being another arterial component of CW. Pressure gradient exists because pulse wave and blood flow arrive into the skull through different cerebral arteries asynchronously, due to arterial tree asymmetry. Therefore, CW and its communicating arteries protect cerebral artery and blood-brain barrier from hemodynamic stress.

Chinese consensus statement on the evaluation and intervention of collateral circulation for ischemic stroke

Background

Collateral circulation is becoming more significant in the individual management strategy of ischemic stroke, there are more data updated recently.

Aim

To make the further acknowledgment of the evaluation and how to improving collateral flow, for better treatment selection.

Method

A panel of experts on stroke providing related statement based on review the results from most up‐to‐date clinical research.

Results

DSA is the gold standard in evaluating all levels of collaterals. CTA can be used for evaluating leptomeningeal collaterals, MRA for CoW, TCD or TCCS can be used as screening tool for primary evaluation. The treatment modalities include direct interventions, such as Extracranial–Intracranial bypass, and indirect interventions, as External counterpulsation and pressor therapy. The consideration of methodology to augment and improve can be considered on an individual basis.

Discussion

In this consensus, we interpret the definition, neuroimaging evaluation, intervention and potential strategy on collaterals in the future.

Conclusion

Assessment of collateral circulation is crucial for selecting therapeutic options, predicting infarction volume and making prognosis after ischemic stroke. Data is still needed to provide therapeutic evidence for many new developed technologies. Until more evidence is available, the clinical significance of applying the new technologies is unclear and perhaps limited.