Anatomy and functionality of leptomeningeal anastomoses: a review

The impacts of venous outflow profiles on outcomes among large vessel occlusion patients receiving endovascular treatment in the late window

OBJECTIVES

To investigate the association between venous outflow (VO) profiles and outcomes among acute ischemic stroke caused by anterior circulation large vessel occlusion (AIS-LVO) patients who had undergone endovascular treatment (EVT) in the late window of 6-24 h from stroke onset.

METHODS

This was a post-hoc analysis of our preceding RESCUE-BT trial, with findings validated in an external cohort. Baseline computed tomographic angiography (CTA) was performed to assess VO using the Cortical Vein Opacification Score (COVES). The primary clinical outcome was functional independence at 90 days (modified Rankin Scale score of 0-2). The adjusted odd ratio (aOR) and confidence interval (CI) were obtained from multivariable logistic regressions.

RESULTS

A total of 440 patients were included in the present study. After identifying the cutoff of COVES by marginal effects approach, enrolled patients were divided into the favorable VO group (COVES 4-6) and the poor VO (COVES 0-3) group. Multivariable logistic regression analysis showed that favorable VO (aOR 2.25; 95% CI 1.31-3.86; p = 0.003) was associated with functional independence. Similar results were detected in the external validation cohort. Among those with poor arterial collateralization, favorable VO was still an independent predictor of functional independence (aOR 2.09; 95% CI 1.06-4.10; p = 0.032).

CONCLUSION

The robust VO profile indicated by COVES 4-6 could promote the frequency of functional independence among AIS-LVO patients receiving EVT in the late window, and the prognostic value of VO was independent of the arterial collateral status.

CLINICAL RELEVANCE STATEMENT

The robust venous outflow profile was a valid predictor for functional independence among AIS-LVO patients receiving EVT in the late window (6-24 h) and the predictive role of venous outflow did not rely on the status of arterial collateral circulation.

The Relationship between CT Angiography Collateral Score and Biochemical Parameters during Acute Ischemic Stroke Caused by Middle Cerebral Artery Infarct

Background/Objectives: Collateral development after AIS is important for prognosis and treatment. In this study, we aimed to investigate the relationship and correlation between biochemical parameters and CT angiography collateral score within the first 9 h and its effect on the neurological outcomes of patients with AIS due to MCA infarction. Methods: A total of 98 patients with MCA infarction were hospitalized for diagnosis and treatment after undergoing CT angiography within 9 h of suffering a stroke. Demographic data, admission biochemical parameters, hospitalization data, and discharge NIHSS scores were recorded. Souza's scoring system for collateral distribution was used to evaluate collaterals. Souza CS system and clinical disability comparison outcomes identified. Results: According to the Souza CS system, 13 patients were in the malignant profile category, and 85 patients were in the good profile category. The NIHSS value of patients with a malignant profile was 27, while the mean NIHSS value of patients with a good profile was 9. There was a statistically significant difference in uric acid, total cholesterol, triglyceride, HDL cholesterol, CRP, hsCRP, D-Dimer, troponin I, vitamin B12, fibrinogen, NSE, homocysteine, aPTT, and INR levels according to collateral distribution. Conclusions: This study demonstrates that biochemical parameters can influence the distribution of malignant and benign collaterals in AIS independent of age and gender.

Development of Collateral Vessels after Anterior Circulation Large Vessel Occlusion in Pediatric Arterial Ischemic Stroke Relates to Stroke Etiology: A Longitudinal Study

BACKGROUND AND PURPOSE

The characteristics of large vessel occlusion (LVO) in the acute phase of pediatric arterial ischemic stroke and their natural history according to stroke etiology are poorly explored. This studied aimed at describing the prevalence and the radiological evolution of LVO in pediatric AIS.

MATERIALS AND METHODS

This single-center retrospective study included consecutive non-neonate children with acute arterial ischemic stroke, intracranial proximal LVO in the anterior circulation (MCA, anterior cerebral artery, and/or ICA), and clinical and imaging follow-up for at least 18 months, during a 9-year period.

RESULTS

Intracranial LVO was observed in 24.8% of patients with anterior circulation arterial ischemic stroke and adequate follow-up (n = 26/105), with a median age of 4.2 years (IQR 0.8-9), sex ratio 1.16. The main stroke etiology associated with LVO was unilateral focal cerebral arteriopathy (n = 12, 46%). During follow-up, a specific pattern of unilateral poststroke anastomotic bridge was observed in 8/26 patients, with the poststroke development of nonperforating collaterals forming a bridge in bypass of the LVO site with visible distal flow, within a median delay of 11 months. The development of unilateral poststroke anastomotic bridge was only observed in patients with unilateral focal cerebral arteriopathy. No patient with this pattern experienced stroke recurrence or further progressive vascular modifications.

CONCLUSIONS

After stroke, the development of unilateral poststroke anastomotic bridge is specifically observed in children with focal cerebral arteriopathy, appearing in the first year after stroke. This clinical-radiologic pattern was not associated with stroke recurrence or arterial worsening, differentiating it from progressive intracranial arteriopathy, such as Moyamoya angiopathy.

Angiographic Pattern of M1 Stenosis Predicts Territorial Stroke in Patients Receiving Aggressive Medication without Stenting

OBJECTIVE

To evaluate the relationship between different angiographic patterns of middle cerebral artery M1 segment stenosis and related territorial stroke in patients receiving aggressive medical treatment without stenting.

METHODS

We retrospectively reviewed our patient registry database to identify ICAS patients diagnosed by digital subtraction angiography between January 2017 and December 2020 and identified 3 different angiographic patterns (normal, shift, and dilation) in 124 patients with M1 stenosis. The association between these patterns and recurrent ischemic stroke in the M1 territory was analyzed.

RESULTS

The rates of recurrent M1 territorial stroke and transient ischemic attack in the normal group, shift group, dilation group and shift-dilation group were 34.5%, 35.0%, 78.3%, and 44.4% respectively. In patients with the shift pattern, the rate of recurrent stroke is significantly higher at a deflection angle ≥9.32° than at a deflection angle <9.32°(P < 0.05). In patients with dilation pattern, the rate of recurrent stroke is significantly higher than patients with non-dilation pattern (72.3% vs. 36.8%, P < 0.05).

CONCLUSIONS

Angiographic patterns of M1 stenosis may predict recurrent territorial strokes, thus providing a surrogate marker to identify high-risk patients for potential endovascular treatment.

Core overestimation of CT perfusion in patients with cardiac insufficiency who had a stroke is mediated by impaired collaterals

BACKGROUND

We hypothesized that left ventricular systolic dysfunction (LVSD) would lead to an ischemic core overestimation in patients with acute ischemic stroke (AIS), and impaired collateral status might partly mediate this effect.

OBJECTIVE

A pixel-based analysis of CT perfusion (CTP) and follow-up CT was undertaken to investigate the optimum CTP thresholds for the ischemic core if overestimation was found.

METHODS

A total of 208 consecutive patients with AIS with large vessel occlusion in the anterior circulation, who received initial CTP evaluation and successful reperfusion, were retrospectively analyzed and divided into an LVSD (left ventricular ejection fraction (LVEF) ratio <50%; n=40) and a normal cardiac function (LVEF≥50%; n=168) group. Ischemic core overestimation was considered when the CTP-derived core was larger than the final infarct volume. We investigated the relationship between cardiac function, probability for core overestimation, and collateral scores using mediation analysis. A pixel-based analysis was undertaken to define the optimum CTP thresholds for ischemic core.

RESULTS

LVSD was independently associated with impaired collaterals (aOR=4.28, 95% CI 2.01 to 9.80, P<0.001) and core overestimation (aOR=2.52, 95% CI 1.07 to 5.72, P=0.030). In mediation analysis, the total effect on core overestimation is composed of the direct effect of LVSD (+17%, P=0.034) and the mediated indirect effect of collateral status (+6%, P=0.020). Collaterals explained 26% of the effect of LVSD on core overestimation. Compared with relative cerebral blood flow (rCBF) thresholds of <35%, <30%, and <20%, a rCBF <25% cut-off point had the highest correlation (r=0.91) and best agreement (mean difference 3.2±7.3 mL) with the final infarct volume to determine the CTP-derived ischemic core in patients with LVSD.

CONCLUSIONS

LVSD increased the possibility of ischemic core overestimation on baseline CTP, partly due to impaired collateral status, and a stricter rCBF threshold should be considered.

FLAIR vascular hyperintensity combined with asymmetrical prominent veins in acute anterior circulation ischemic stroke: prediction of collateral circulation and clinical outcome

BACKGROUND

To investigate the value of fluid-attenuated inversion recovery vascular hyperintensity (FVH) within asymmetrical prominent veins sign (APVS) on susceptibility-weighted imaging predicting collateral circulation and prognosis in patients with acute anterior circulation ischemic stroke.

METHOD

Patients with severe stenosis or occlusion of ICA or MCA M1, who underwent MRI within 72 h from stroke onset were reviewed. The Alberta Stroke Program Early CT Score was used to evaluate the volume of infarction on DWI, the degree of FVH and APVS. Spearman correlation analysis was used to evaluate the correlation between FVH and APVS. All patients were divided into the good prognosis group and the poor prognosis group according to the score of the modified ranking scale (mRS) 90 days after the stroke. Logistic regression analysis was used to explore the relationship between FVH and APVS and functional prognosis, while receiver operating characteristic (ROC) curves were plotted to assess the value of FVH and APVS in predicting prognosis.

RESULTS

Spearman correlation analysis revealed moderate positive correlations between FVH and APVS (r = 0.586, P < 0.001). The poor prognosis group had a higher rate of a history of atrial fibrillation, a larger cerebral infarction volume, a higher NIHSS score at admission, and a higher FVH and APVS score compared with the good prognosis group (all P < 0.05). A further logistic regression indicated that the NIHSS score, cerebral infarction volume, FVH and APVS were independent risk factors for a poor functional prognosis. In terms of FVH, APVS, alone and their combination for the diagnosis of poor prognosis, the sensitivity, specificity, area under the ROC curve (AUC), and 95% confidence interval (CI) were 86.8%, 83.3%, 0.899 (95% CI 0.830-0.968); 60.5%, 93.7%, 0.818 (95% CI 0.723-0.912); 86.8%, 89.6%, 0.921 (95% CI 0.860-0.981), respectively.

CONCLUSION

The presence of FVH and APVS can provide a comprehensive assessment of collateral circulation from the perspective of veins and arteries, and the correlation between the two is positively correlated. Both of them were independent risk factors for poor prognosis, their combination is complementary and can improve the predictive value.

The role of leptomeningeal collaterals in redistributing blood flow during stroke

Leptomeningeal collaterals (LMCs) connect the main cerebral arteries and provide alternative pathways for blood flow during ischaemic stroke. This is beneficial for reducing infarct size and reperfusion success after treatment. However, a better understanding of how LMCs affect blood flow distribution is indispensable to improve therapeutic strategies. Here, we present a novel in silico approach that incorporates case-specific in vivo data into a computational model to simulate blood flow in large semi-realistic microvascular networks from two different mouse strains, characterised by having many and almost no LMCs between middle and anterior cerebral artery (MCA, ACA) territories. This framework is unique because our simulations are directly aligned with in vivo data. Moreover, it allows us to analyse perfusion characteristics quantitatively across all vessel types and for networks with no, few and many LMCs. We show that the occlusion of the MCA directly caused a redistribution of blood that was characterised by increased flow in LMCs. Interestingly, the improved perfusion of MCA-sided microvessels after dilating LMCs came at the cost of a reduced blood supply in other brain areas. This effect was enhanced in regions close to the watershed line and when the number of LMCs was increased. Additional dilations of surface and penetrating arteries after stroke improved perfusion across the entire vasculature and partially recovered flow in the obstructed region, especially in networks with many LMCs, which further underlines the role of LMCs during stroke.

Disruption of Vitamin D Signaling Impairs Adaptation of Cerebrocortical Microcirculation to Carotid Artery Occlusion in Hyperandrogenic Female Mice

Vitamin D deficiency contributes to the pathogenesis of age-related cerebrovascular diseases, including ischemic stroke. Sex hormonal status may also influence the prevalence of these disorders, indicated by a heightened vulnerability among postmenopausal and hyperandrogenic women. To investigate the potential interaction between sex steroids and disrupted vitamin D signaling in the cerebral microcirculation, we examined the cerebrovascular adaptation to unilateral carotid artery occlusion (CAO) in intact, ovariectomized, and hyperandrogenic female mice with normal or functionally inactive vitamin D receptor (VDR). We also analyzed the morphology of leptomeningeal anastomoses, which play a significant role in the compensation. Ablation of VDR by itself did not impact the cerebrocortical adaptation to CAO despite the reduced number of pial collaterals. While ovariectomy did not undermine compensatory mechanisms following CAO, androgen excess combined with VDR inactivity resulted in prolonged hypoperfusion in the cerebral cortex ipsilateral to the occlusion. These findings suggest that the cerebrovascular consequences of disrupted VDR signaling are less pronounced in females, providing a level of protection even after ovariectomy. Conversely, even short-term androgen excess with lacking VDR signaling may lead to unfavorable outcomes of ischemic stroke, highlighting the complex interplay between sex steroids and vitamin D in terms of cerebrovascular diseases.

Computational modeling of multiscale collateral blood supply in a whole-brain-scale arterial network

The cerebral arterial network covering the brain cortex has multiscale anastomosis structures with sparse intermediate anastomoses (O[102] μm in diameter) and dense pial networks (O[101] μm in diameter). Recent studies indicate that collateral blood supply by cerebral arterial anastomoses has an essential role in the prognosis of acute ischemic stroke caused by large vessel occlusion. However, the physiological importance of these multiscale morphological properties-and especially of intermediate anastomoses-is poorly understood because of innate structural complexities. In this study, a computational model of multiscale anastomoses in whole-brain-scale cerebral arterial networks was developed and used to evaluate collateral blood supply by anastomoses during middle cerebral artery occlusion. Morphologically validated cerebral arterial networks were constructed by combining medical imaging data and mathematical modeling. Sparse intermediate anastomoses were assigned between adjacent main arterial branches; the pial arterial network was modeled as a dense network structure. Blood flow distributions in the arterial network during middle cerebral artery occlusion simulations were computed. Collateral blood supply by intermediate anastomoses increased sharply with increasing numbers of anastomoses and provided one-order-higher flow recoveries to the occluded region (15%-30%) compared with simulations using a pial network only, even with a small number of intermediate anastomoses (≤10). These findings demonstrate the importance of sparse intermediate anastomoses, which are generally considered redundant structures in cerebral infarction, and provide insights into the physiological significance of the multiscale properties of arterial anastomoses.

Longitudinal evaluation of the functional connectivity changes in the secondary somatosensory cortex (S2) of the monkey brain during acute stroke

Background

Somatosensory deficits are frequently seen in acute stroke patients and may recover over time and affect functional outcome. However, the underlying mechanism of function recovery remains poorly understood. In the present study, progressive function alteration of the secondary somatosensory cortex (S2) and its relationship with regional perfusion and neurological outcome were examined using a monkey model of stroke.

Methods and materials

Rhesus monkeys (n = 4) were induced with permanent middle cerebral artery occlusion (pMCAo). Resting-state functional MRI, dynamic susceptibility contrast perfusion MRI, diffusion-weighted, T₁ and T₂ weighted images were collected before surgery and at 4-6, 48, and 96 h post stroke on a 3T scanner. Progressive changes of relative functional connectivity (FC), cerebral blood flow (CBF), and CBF/Tmax (Time to Maximum) of affected S2 regions were evaluated. Neurological deficits were assessed using the Spetzler approach.

Results

Ischemic lesion was evidently seen in the MCA territory including S2 in each monkey. Relative FC of injured S2 regions decreased substantially following stroke. Spetzler scores dropped substantially at 24 h post stroke but slightly recovered from Day 2 to Day 4. Relative FC progressively increased from 6 to 48 and 96 h post stroke and correlated significantly with relative CBFand CBF/Tmax changes.

Conclusion

The present study revealed the progressive alteration of function connectivity in S2 during acute stroke. The preliminary results suggested the function recovery might start couple days post occlusion and collateral circulation might play a key role in the recovery of somatosensory function after stroke insult. The relative function connectivity in S2 may provide additional information for prediction of functional outcome in stroke patients.

Preferential delivery of lipid-ligand conjugated DNA/RNA heteroduplex oligonucleotide to ischemic brain in hyperacute stage

Antisense oligonucleotide (ASO) is a major tool used for silencing pathogenic genes. For stroke in the hyperacute stage, however, the ability of ASO to regulate genes is limited by its poor delivery to the ischemic brain owing to sudden occlusion of the supplying artery. Here we show that, in a mouse model of permanent ischemic stroke, lipid-ligand conjugated DNA/RNA heteroduplex oligonucleotide (lipid-HDO) was unexpectedly delivered 9.6 times more efficiently to the ischemic area of the brain than to the contralateral non-ischemic brain and achieved robust gene knockdown and change of stroke phenotype, despite a 90% decrease in cerebral blood flow in the 3 h after occlusion. This delivery to neurons was mediated via receptor-mediated transcytosis by lipoprotein receptors in brain endothelial cells, the expression of which was significantly upregulated after ischemia. This study provides proof-of-concept that lipid-HDO is a promising gene-silencing technology for stroke treatment in the hyperacute stage.

A multiscale computational framework to evaluate flow alterations during mechanical thrombectomy for treatment of ischaemic stroke

The treatment of ischaemic stroke increasingly relies upon endovascular procedures known as mechanical thrombectomy (MT), which consists in capturing and removing the clot with a catheter-guided stent while at the same time applying external aspiration with the aim of reducing haemodynamic loads during retrieval. However, uniform consensus on procedural parameters such as the use of balloon guide catheters (BGC) to provide proximal flow control, or the position of the aspiration catheter is still lacking. Ultimately the decision is left to the clinician performing the operation, and it is difficult to predict how these treatment options might influence clinical outcome. In this study we present a multiscale computational framework to simulate MT procedures. The developed framework can provide quantitative assessment of clinically relevant quantities such as flow in the retrieval path and can be used to find the optimal procedural parameters that are most likely to result in a favorable clinical outcome. The results show the advantage of using BGC during MT and indicate small differences between positioning the aspiration catheter in proximal or distal locations. The framework has significant potential for future expansions and applications to other surgical treatments.

Therapeutic Induction of Collateral Flow

Therapeutic induction of collateral flow as a means to salvage tissue and improve outcome from acute ischemic stroke is a promising approach in the era in which endovascular therapy is no longer time-dependent but collateral-dependent. The importance of collateral flow enhancement as a therapeutic for acute ischemic stroke extends beyond those patients with large amounts of salvageable tissue. It also has the potential to extend the time window for reperfusion therapies in patients who are ineligible for endovascular thrombectomy. In addition, collateral enhancement may be an important adjuvant to neuroprotective agents by providing a more robust vascular route for which treatments can gain access to at risk tissue. However, our understanding of collateral hemodynamics, including under comorbid conditions that are highly prevalent in the stroke population, has hindered the efficacy of collateral flow augmentation for improving stroke outcome in the clinical setting. This review will discuss our current understanding of pial collateral function and hemodynamics, including vasoactivity that is critical for enhancing penumbral perfusion. In addition, mechanisms by which collateral flow can be increased during acute ischemic stroke to limit ischemic injury, that may be different depending on the state of the brain and vasculature prior to stroke, will also be reviewed.

Role of Vitamin D Deficiency in the Pathogenesis of Cardiovascular and Cerebrovascular Diseases

Deficiency in vitamin D (VitD), a lipid-soluble vitamin and steroid hormone, affects approximately 24% to 40% of the population of the Western world. In addition to its well-documented effects on the musculoskeletal system, VitD also contributes importantly to the promotion and preservation of cardiovascular health via modulating the immune and inflammatory functions and regulating cell proliferation and migration, endothelial function, renin expression, and extracellular matrix homeostasis. This brief overview focuses on the cardiovascular and cerebrovascular effects of VitD and the cellular, molecular, and functional changes that occur in the circulatory system in VitD deficiency (VDD). It explores the links among VDD and adverse vascular remodeling, endothelial dysfunction, vascular inflammation, and increased risk for cardiovascular and cerebrovascular diseases. Improved understanding of the complex role of VDD in the pathogenesis of atherosclerotic cardiovascular diseases, stroke, and vascular cognitive impairment is crucial for all cardiologists, dietitians, and geriatricians, as VDD presents an easy target for intervention.

Neutrophil dynamics and inflammaging in acute ischemic stroke: A transcriptomic review

Stroke is among the leading causes of death and disability worldwide. Restoring blood flow through recanalization is currently the only acute treatment for cerebral ischemia. Unfortunately, many patients that achieve a complete recanalization fail to regain functional independence. Recent studies indicate that activation of peripheral immune cells, particularly neutrophils, may contribute to microcirculatory failure and futile recanalization. Stroke primarily affects the elderly population, and mortality after endovascular therapies is associated with advanced age. Previous analyses of differential gene expression across injury status and age identify ischemic stroke as a complex age-related disease. It also suggests robust interactions between stroke injury, aging, and inflammation on a cellular and molecular level. Understanding such interactions is crucial in developing effective protective treatments. The global stroke burden will continue to increase with a rapidly aging human population. Unfortunately, the mechanisms of age-dependent vulnerability are poorly defined. In this review, we will discuss how neutrophil-specific gene expression patterns may contribute to poor treatment responses in stroke patients. We will also discuss age-related transcriptional changes that may contribute to poor clinical outcomes and greater susceptibility to cerebrovascular diseases.

VEGF to CITED2 ratio predicts the collateral circulation of acute ischemic stroke

Objective

The research objective was to evaluate the predicting role of the vascular endothelial growth factor to CBP/P300-interacting transactivator with Glu/Asp-rich C-terminal domain 2 Ratio (VEGF/CITED2) from peripheral blood mononuclear cells (PBMCs) in the collateral circulation of acute ischemic stroke (AIS).

Methods

In an observational study of patients with AIS, the western blot was applied to test the protein expression of VEGF and CITED2. Then, we calculated the VEGF/CITED2 and collected other clinical data. Binary logistic regression analysis between collateral circulation and clinical data was performed. Finally, receiver operating characteristic (ROC) curve analysis was used to explore the predictive value of VEGF/CITED2.

Results

A total of 67 patients with AIS were included in the study. Binary logistic regression analysis indicated the VEGF/CITED2 (OR 165.79, 95%CI 7.25–3,791.54, P = 0.001) was an independent protective factor. The ROC analyses showed an area under the ROC curve of the VEGF/CITED2 was 0.861 (95%CI 0.761–0.961). The optimal cutoff value of 1.013 for VEGF/CITED2 had a sensitivity of 89.1% and a specificity of 85.7%.

Conclusion

In patients with AIS, the VEGF/CITED2 was related to the establishment of collateral circulation. The VEGF/CITED2 is a potentially valuable biomarker for predicting collateral circulation.

Clinical trial registration

ClinicalTrials.gov, identifier: NCT05345366.

Flow reversal in distal collaterals as a possible mechanism of delayed intraparenchymal hemorrhage after flow diversion treatment of cerebral aneurysms

Background and Purpose: Delayed intraparenchymal hemorrhages (DIPHs) are one of the most serious complications of cerebral aneurysm treatment with flow diverters (FD), yet their causes are largely unknown. This study analyzes distal hemodynamic alterations induced by the treatment of intracranial aneurysms with FDs.

Methods: A realistic model of the brain arterial network was constructed from MRA images and extended with a constrained constructive optimization technique down to vessel diameters of approximately 50μm. Different variants of the circle of Willis were created by alternatively occluding communicating arteries. Collateral vessels connecting different arterial trees were then added to the model, and a distributed lumped parameter approach was used to model the pulsatile blood flow in the arterial network. The treatment of an ICA aneurysm was modeled by changing the local resistance, flow inertia, and compliance of the aneurysmal segment.

Results: The maximum relative change in distal pressure induced by the aneurysm treatment was below 1%. However, for certain combinations of the circle of Willis and distal collateralization, important flow reversals (with a wall shear stress larger than approximately 1.0 dyne/cm2) were observed in collateral vessels, both ipsilaterally and contralaterally to the treated aneurysm.

Conclusion: This study suggests the hypothesis that flow diverters treatment of intracranial aneurysms could cause important flow reversal in distal collaterals. Flow reversal has previously been shown to be pro-inflammatory and pro-atherogenic and could therefore have a detrimental effect on these collateral vessels, and thus could be a suitable explanation of DIPHs, while the small distal pressure increase is not.

Determining Clinically-Viable Biomarkers for Ischaemic Stroke Through a Mechanistic and Machine Learning Approach

Assessment of distal cerebral perfusion after ischaemic stroke is currently only possible through expensive and time-consuming imaging procedures which require the injection of a contrast medium. Alternative approaches that could indicate earlier the impact of blood flow occlusion on distal cerebral perfusion are currently lacking. The aim of this study was to identify novel biomarkers suitable for clinical implementation using less invasive diagnostic techniques such as Transcranial Doppler (TCD). We used 1D modelling to simulate pre- and post-stroke velocity and flow wave propagation in a typical arterial network, and Sobol’s sensitivity analysis, supported by the use of Gaussian process emulators, to identify biomarkers linked to cerebral perfusion. We showed that values of pulsatility index of the right anterior cerebral artery > 1.6 are associated with poor perfusion and may require immediate intervention. Three additional biomarkers with similar behaviour, all related to pulsatility indices, were identified. These results suggest that flow pulsatility measured at specific locations could be used to effectively estimate distal cerebral perfusion rates, and ultimately improve clinical diagnosis and management of ischaemic stroke.

Pre-stroke Physical Activity and Cerebral Collateral Circulation in Ischemic Stroke: A Potential Therapeutic Relationship?

Favorable cerebral collateral circulation contributes to hindering penumbral tissue from progressing to infarction and is associated with positive clinical outcomes after stroke. Given its clinical importance, improving cerebral collateral circulation is considered a therapeutic target to reduce burden after stroke. We provide a hypothesis-generating discussion on the potential association between pre-stroke physical activity and cerebral collateral circulation in ischemic stroke. The recruitment of cerebral collaterals in acute ischemic stroke may depend on anatomical variations, capacity of collateral vessels to vasodilate, and individual risk factors. Physical activity is associated with improved cerebral endothelial and vascular function related to vasodilation and angiogenic adaptations, and risk reduction in individual risk factors. More research is needed to understand association between cerebral collateral circulation and physical activity. A presentation of different methodological considerations for measuring cerebral collateral circulation and pre-stroke physical activity in the context of acute ischemic stroke is included. Opportunities for future research into cerebral collateral circulation, physical activity, and stroke recovery is presented.

Stage-Dependent Cerebral Blood Flow and Leukoaraiosis Couplings in Subcortical Ischemic Vascular Disease and Alzheimer's Disease

Background:

Alzheimer’s disease (AD) and subcortical ischemic vascular disease (SIVD) have both been associated with white matter hyperintensities (WMHs) and altered cerebral blood flow (CBF) although the etiology of AD is still unclear.

Objective:

To test the hypothesis that CBF and WMHs have differential effects on cognition and that the relationship between CBF and WMHs changes with the subtypes and stages of dementia.

Methods:

Forty-two patients with SIVD, 50 patients with clinically-diagnosed AD, and 30 cognitively-normal subjects were included. Based on the Clinical Dementia Rating (CDR), the patients were dichotomized into early-stage (CDR = 0.5) and late-stage (CDR = 1 or 2) groups. CBF and WMH metrics were derived from magnetic resonance imaging and correlated with cognition.

Results:

Hierarchical linear regression revealed that CBF metrics had distinct contribution to global cognition, memory, and attention, whereas WMH metrics had distinct contribution to executive function (all p < 0.05). In SIVD, the WMHs in frontotemporal areas correlated with the CBF in bilateral thalami at the early stage; the correlation then became between the WMHs in basal ganglia and the CBF in frontotemporal areas at the late stage. A similar corticosubcortical coupling was observed in AD but involved fewer areas.

Conclusion:

A stage-dependent coupling between CBF and WMHs was identified in AD and SIVD, where the extent of cortical WMHs correlated with subcortical CBF for CDR = 0.5, whereas the extent of subcortical WMHs correlated with cortical CBF for CDR = 1–2.

Occult blood flow patterns distal to an occluded artery in acute ischemic stroke

Residual blood flow distal to an arterial occlusion in patients with acute ischemic stroke (AIS) is associated with favorable patient outcome. Both collateral flow and thrombus permeability may contribute to such residual flow. We propose a method for discriminating between these two mechanisms, based on determining the direction of flow in multiple branches distal to the occluding thrombus using dynamic Computed Tomography Angiography (dynamic CTA). We analyzed dynamic CTA data of 30 AIS patients and present patient-specific cases that identify typical blood flow patterns and velocities. We distinguished patterns with anterograde (N = 10), retrograde (N = 9), and both flow directions (N = 11), with a large variability in velocities for each flow pattern. The observed flow patterns reflect the interplay between permeability and collaterals. The presented method characterizes distal flow and provides a tool to study patient-specific distal tissue perfusion.

A Review of Risk Factors and Predictors for Hemorrhagic Transformation in Patients with Acute Ischemic Stroke

Acute ischemic strokes (AIS) and hemorrhagic strokes lead to disabling neuropsychiatric and cognitive deficits. A serious and fatal complication of AIS is the occurrence of hemorrhagic transformation (HT). HT is cerebral bleeding that occurs after an ischemic event in the infarcted areas. This review summarises how specific risk factors such as demographic factors like age, gender, and race/ethnicity, comorbidities including essential hypertension, atrial fibrillation, diabetes mellitus, congestive heart failure, and ischemic heart disease along with predictors like higher NIHSS score, larger infarction size, cardioembolic strokes, systolic blood pressure/pulse pressure variability, higher plasma glucose levels, and higher body temperature during ischemic event, lower low-density lipoprotein and total cholesterol, early ischemic changes on imaging modalities, and some rare causes make an individual more susceptible to developing HT. We also discuss few other risk factors such as the role of blood-brain barrier, increased arterial stiffness, and globulin levels in patients postreperfusion using thrombolysis and mechanical thrombectomy. In addition, we discuss the implications of dual antiplatelet therapy and the length of treatment in reference to the incidence of developing HT. Current research into inflammatory mediators and biomarkers such as Cyclooxygenase-2, matrix metalloproteinases, and soluble ST2 and their potential role as treatment options for HT is also briefly discussed. Finally, this review calls for more research into use of dual antiplatelet and the timing of antiplatelet and anticoagulant use in reference to hemorrhagic transformation.

Three-Dimensional Iron Oxide Nanoparticle-Based Contrast-Enhanced Magnetic Resonance Imaging for Characterization of Cerebral Arteriogenesis in the Mouse Neocortex

Purpose: Subsurface blood vessels in the cerebral cortex have been identified as a bottleneck in cerebral perfusion with the potential for collateral remodeling. However, valid techniques for non-invasive, longitudinal characterization of neocortical microvessels are still lacking. In this study, we validated contrast-enhanced magnetic resonance imaging (CE-MRI) for in vivo characterization of vascular changes in a model of spontaneous collateral outgrowth following chronic cerebral hypoperfusion. Methods: C57BL/6J mice were randomly assigned to unilateral internal carotid artery occlusion or sham surgery and after 21 days, CE-MRI based on T2*-weighted imaging was performed using ultra-small superparamagnetic iron oxide nanoparticles to obtain subtraction angiographies and steady-state cerebral blood volume (ss-CBV) maps. First pass dynamic susceptibility contrast MRI (DSC-MRI) was performed for internal validation of ss-CBV. Further validation at the histological level was provided by ex vivo serial two-photon tomography (STP). Results: Qualitatively, an increase in vessel density was observed on CE-MRI subtraction angiographies following occlusion; however, a quantitative vessel tracing analysis was prone to errors in our model. Measurements of ss-CBV reliably identified an increase in cortical vasculature, validated by DSC-MRI and STP. Conclusion: Iron oxide nanoparticle-based ss-CBV serves as a robust, non-invasive imaging surrogate marker for neocortical vessels, with the potential to reduce and refine preclinical models targeting the development and outgrowth of cerebral collateralization.

Cerebral hyperperfusion syndrome after intracranial stenting: Case report and systematic review

BACKGROUND

Cerebral Hyperperfusion Syndrome (CHS) is an uncommon complication observed after intracranial angioplasty or stenting procedures. Given to the increasing use of new devices for intracranial angioplasty and stenting (INCS), in selected patients with high ischemic stroke risk, an equally increasing knowledge of complications related to these procedures is mandatory.Case description: a 63-year-old man was diagnosed with an hyperperfusion syndrome after percutaneous angioplasty and stenting for severe symptomatic right internal carotid artery (ICA) siphon stenosis. After treatment he complained generalized seizures and respiratory failure. While conventional imaging did not demonstrate any acute brain lesions, Pseudo-Continuous Arterial Spin Labeling (PCASL) Perfusion MRI early documented right hemisphere blood flow increase suggestive for CHS.

CONCLUSIONS

Monitoring of perfusion changes after INCS could play an important a role in determining patients with high risk of CHS. ASL Perfusion MRI might be used for promptly, early diagnosis of CHS after treatment of severe intracranial artery stenosis.

Cerebral white matter vasculature: still uncharted?

White matter vasculature plays a major role in the pathophysiology of permanent neurological deficits following a stroke or progressive cognitive alteration related to small vessel disease. Thus, knowledge of the complex vascularization and functional aspects of the deep white matter territories is paramount to comprehend clinical manifestations of brain ischemia. This review provides a structured presentation of the existing knowledge of the vascularization of the human cerebral white matter from seminal historical studies to the current literature. First, we revisit the highlights of prenatal development of the endoparenchymal telencephalic vascular system that are crucial for the understanding of vessel organization in the adult. Second, we reveal the tangled history of debates on the existence, clinical significance, and physiological role of leptomeningeal anastomoses. Then, we present how conceptions on white matter vascularization transitioned from the mixed ventriculopetal/ventriculofugal theory, in which a low-flow area was interposed in between concurrent arterial flows, to the purely ventriculopetal theory. The latter model explains variable white matter sensitivity to ischemia by various organizations of ventriculopetal vessel terminals having different origin/length properties and interconnection patterns. Next, arteries supplying primarily the white matter are described according to their length and overall structure. Furthermore, the known distribution territories, to date, are studied in relation to primary anatomical structures of the human cerebral white matter, emphasizing the sparsity of the "ground-truth" data available in the literature. Finally, the implications for both large vessel occlusion and chronic small vessel disease are discussed, as well as the insights from neuroimaging. All things considered, we identify the need for further research on deep white matter vascularization, especially regarding the arterial supply of white matter fiber tracts.

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.

Hemodynamics of Leptomeningeal Collaterals after Large Vessel Occlusion and Blood Pressure Management with Endovascular Treatment

Endovascular therapy (EVT) is an effective treatment for ischemic stroke due to large vessel occlusion (LVO). Unlike intravenous thrombolysis, EVT enables visualization of the restoration of blood flow, also known as successful reperfusion in real time. However, until successful reperfusion is achieved, the survival of the ischemic brain is mainly dependent on blood flow from the leptomeningeal collaterals (LMC). It plays a critical role in maintaining tissue perfusion after LVO via pre-existing channels between the arborizing pial small arteries or arterioles overlying the cerebral hemispheres. In the ischemic territory where the physiologic cerebral autoregulation is impaired and the pial arteries are maximally dilated within their capacity, the direction and amount of LMC perfusion rely on the systemic perfusion, which can be estimated by measuring blood pressure (BP). After the EVT procedure, treatment focuses on mitigating the risk of hemorrhagic transformation, potentially via BP reduction. Thus, BP management may be a key component of acute care for patients with LVO stroke. However, the guidelines on BP management during and after EVT are limited, mostly due to the scarcity of high-level evidence on this issue. In this review, we aim to summarize the anatomical and physiological characteristics of LMC to maintain cerebral perfusion after acute LVO, along with a landscape summary of the literature on BP management in endovascular treatment. The objective of this review is to describe the mechanistic association between systemic BP and collateral perfusion after LVO and thus provide clinical and research perspectives on this topic.

Thomas Willis Lecture: Targeting Brain Arterioles for Acute Stroke Treatment

[Figure: see text].

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

[Figure: see text].

Progression of cerebral infarction before and after thrombectomy is modified by prehospital pathways

Background

Evidence of the consequences of different prehospital pathways before mechanical thrombectomy (MT) in large vessel occlusion stroke is inconclusive. The aim of this study was to investigate the infarct extent and progression before and after MT in directly admitted (mothership) versus transferred (drip and ship) patients using the Alberta Stroke Program Early CT Score (ASPECTS).

Methods

ASPECTS of 535 consecutive large vessel occlusion stroke patients eligible for MT between 2015 to 2019 were retrospectively analyzed for differences in the extent of baseline, post-referral, and post-recanalization infarction between the mothership and drip and ship pathways. Time intervals and transport distances of both pathways were analyzed. Multiple linear regression was used to examine the association between infarct progression (baseline to post-recanalization ASPECTS decline), patient characteristics, and logistic key figures.

Results

ASPECTS declined during transfer (9 (8–10) vs 7 (6-9), p<0.0001), resulting in lower ASPECTS at stroke center presentation (mothership 9 (7–10) vs drip and ship 7 (6–9), p<0.0001) and on follow-up imaging (mothership 7 (4–8) vs drip and ship 6 (3–7), p=0.001) compared with mothership patients. Infarct progression was significantly higher in transferred patients (points lost, mothership 2 (0–3) vs drip and ship 3 (2–6), p<0.0001). After multivariable adjustment, only interfacility transfer, preinterventional clinical stroke severity, the degree of angiographic recanalization, and the duration of the thrombectomy procedure remained predictors of infarct progression (R²=0.209, p<0.0001).

Conclusions

Infarct progression and postinterventional infarct extent, as assessed by ASPECTS, varied between the drip and ship and mothership pathway, leading to more pronounced infarction in transferred patients. ASPECTS may serve as a radiological measure to monitor the benefit or harm of different prehospital pathways for MT.

The Mechanism of Macular Sparing

Patients with homonymous hemianopia sometimes show preservation of the central visual fields, ranging up to 10°. This phenomenon, known as macular sparing, has sparked perpetual controversy. Two main theories have been offered to explain it. The first theory proposes a dual representation of the macula in each hemisphere. After loss of one occipital lobe, the back-up representation in the remaining occipital lobe is postulated to sustain ipsilateral central vision in the blind hemifield. This theory is supported by studies showing that some midline retinal ganglion cells project to the wrong hemisphere, presumably driving neurons in striate cortex that have ipsilateral receptive fields. However, more recent electrophysiological recordings and neuroimaging studies have cast doubt on this theory by showing only a minuscule ipsilateral field representation in early visual cortical areas. The second theory holds that macular sparing arises because the occipital pole, where the macula is represented, remains perfused after occlusion of the posterior cerebral artery because it receives collateral flow from the middle cerebral artery. An objection to this theory is that it cannot account for reports of macular sparing in patients after loss of an entire occipital lobe. On close scrutiny, such reports turn out to be erroneous, arising from inadequate control of fixation during visual field testing. Patients seem able to detect test stimuli on their blind side within the macula or along the vertical meridian because they make surveillance saccades. A purported treatment for hemianopia, called vision restoration therapy, is based on this error. The dual perfusion theory is supported by anatomical studies showing that the middle cerebral artery perfuses the occipital pole in many individuals. In patients with hemianopia from stroke, neuroimaging shows preservation of the occipital pole when macular sparing is present. The frontier dividing the infarcted territory of the posterior cerebral artery and the preserved territory of the middle cerebral artery is variable, but always falls within the representation of the macula, because the macula is so highly magnified. For physicians, macular sparing was an important neurological sign in acute hemianopia because it signified a posterior cerebral artery occlusion. Modern neuroimaging has supplanted the importance of that clinical sign but at the same time confirmed its validity. For patients, macular sparing remains important because it mitigates the impact of hemianopia and preserves the ability to read fluently. Expected final online publication date for the Annual Review of Vision Science, Volume 7 is September 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

The diagnostic reliability and validity of noninvasive imaging modalities to assess leptomeningeal collateral flow for ischemic stroke patients: A systematic review and meta-analysis

Leptomeningeal collateral flow (LMF) is associated with infarct area and clinical outcome for ischemic stroke patients. Although LMF can be detected by multiple imaging methods, but their diagnostic performance is uncertain.The aim of this study was to evaluate the diagnostic validity or reliability of noninvasive image methods in assessing LMF.Databases included PubMed, Web of Science, Embase, and Cochrane Library.Original observational cohort studies.Ischemic stroke patients.Different noninvasive image methods to assess LMF.Newcastle-Ottawa Scale to evaluate the quality of the studies; forest plot to show pooled results; I2 and Egger test to evaluate the heterogeneity and publication bias.Thirty of the 126 selected studies were eligible. For CT angiography, the interobserver agreement ranged from 0.494 to 0.93 and weighted kappa was 0.888; for patients receiving thrombolysis or endovascular treatment, 0.68 to 0.91; 0.494 to 0.89 for the 2-point system, 0.60 to 0.93 for the 3-point system, 0.68 to 0.87 for the system of >4 points; area under the curve (AUC) was 0.78. For perfusion computed tomography (CTP), the interobserver agreement ranged from 0.724 to 0.872; for patients receiving thrombolysis or endovascular treatment, 0.74 to 0.872; 0.724 for the 2-point system, 0.783 to 0.953 for the 3-point system; the intraobserver agreement was 0.884; AUC was 0.826. For MRI-fluid attenuated inversion recovery (FLAIR), the interobserver agreement ranged from 0.58 to 0.86; for patients receiving thrombolysis or endovascular treatment, 0.75 to 0.86; 0.86 for the two-point system, 0.77 to 0.87 for the system of more than 5 points; AUC was 0.82.No pooled data of CTP and FLAIR. The difference cohort study had difference bias. The unpublished data were not included.CT angiography is a good tool for assessing LMF. CTP shows a good validity and reliability, but its diagnostic value needs more evidence. FLAIR is a good modality to assess LMF. These image methods had better validity and reliability to evaluate LMF of patients receiving thrombolysis or endovascular treatment than all ischemic stroke patients.

Watershed subarachnoid hemorrhage after middle cerebral artery rescue stenting in patients with acute ischemic stroke

Cortical subarachnoid hemorrhage is an infrequent subtype of non-aneurysmal subarachnoid hemorrhage, rarely reported in watershed territories (wSAH) after carotid stenting. It has never been reported after treatment of middle cerebral artery stenosis (MCAS) that is increasingly used in selected patients, as rescue treatment of failed mechanical thrombectomy, due to recent advancements in endovascular interventions. We present a series of patients with MCAS that developed a wSAH after stenting.

Modelling the leptomeningeal collateral circulation during acute ischaemic stroke

A novel model of the leptomeningeal collateral circulation is created by combining data from multiple sources with statistical scaling laws. The extent of the collateral circulation is varied by defining a collateral vessel probability. Blood flow and pressure are simulated using a one-dimensional steady state blood flow model. The leptomeningeal collateral vessels provide significant flow during a stroke. The pressure drop over an occlusion predicted by the model ranges between 60 and 85 mmHg depending on the extent of the collateral circulation. The linear transport of contrast material was simulated in the circulatory network. The time delay of peak contrast over an occlusion is 3.3 s in the model, and 2.1 s (IQR 0.8-4.0 s) when measured in dynamic CTA data of acute ischaemic stroke patients. Modelling the leptomeningeal collateral circulation could lead to better estimates of infarct volume and patient outcome.

Clarifying the effects of diabetes on the cerebral circulation: Implications for stroke recovery and beyond

Given the sheer increased number of victims per year and the availability of only one effective treatment, acute ischemic stroke (AIS) remains to be one of the most under-treated serious diseases. Diabetes not only increases the incidence of ischemic stroke, but amplifies the ischemic damage, upon which if patients with diabetes suffer from stroke, he/she will confront increased risks of long-term functional deficits. The grim reality makes it a pressing need to intensify efforts at the basic science level to understand how diabetes impairs stroke recovery. This review retrospects the clinical and experimental studies in order to elucidate the detrimental effect of diabetes on cerebrovascular circulation including the major arteries/arterioles, collateral circulation, and neovascularization to shed light on further exploration of novel strategies for cerebral circulation protection before and after AIS in patients with diabetes.

Role of neuroimaging before reperfusion therapy. Part 1 - IV thrombolysis - Review

This review paper summarises the yield of the different imaging modalities in the evaluation of patients for IV thrombolysis. Non-contrast CT and CTA or brain MRI combined with MRA are the recommended sequences for the evaluation of patients within the 4.5 hours time window. Multimodal MRI (DWI/PWI), and more recently, CT perfusion, offer reliable surrogate of salvageable penumbra, the target mismatch, which is now currently used as selection criteria for revascularisation treatment in an extended time window. Those sequences may also help the physician for the management of other limited cases when the diagnosis of acute ischemic stroke is difficult. Another approach the DWI/FLAIR mismatch has been proposed to identify among wake-up stroke patients those who have been experiencing an acute ischemic stroke evolving from less than 4.5hrs. Other biomarkers, such as the clot imaging on MRI and CT, help to predict the recanalisation rate after IVT, while the impact of the presence microbleeds on MRI remains to be determined.

Semiautomatic cerebrovascular territory mapping based on dynamic ASL MR angiography without vessel-encoded labeling

PURPOSE

Characterizing vessel territories can provide crucial information for evaluation of cerebrovascular disorders. In this study, we present a novel postprocessing pipeline for vascular territorial imaging of cerebral arteries based on a noncontrast enhanced time-resolved 4D magnetic resonance angiography (MRA).

METHODS

Eight healthy participants, 1 Moyamoya patient, and 1 arteriovenous malformations patient were recruited. Territorial segmentation and relative blood flow rate calculations of cerebral arteries including left and right middle cerebral arteries and left and right posterior cerebral arteries were carried out based on the 4D MRA-derived arterial arrival time maps of intracranial vessels.

RESULTS

Among healthy young subjects, the average relative blood flow rate values corresponding to left and right middle cerebral arteries and left and right posterior cerebral arteries were 35.9 ± 5.9%, 32.9 ± 7.5%, 15.4 ± 3.8%, and 15.9 ± 2.5%, respectively. Excellent agreement was observed between relative blood flow rate values obtained from the proposed 4D MRA-based method and reference 2D phase contrast MRI. Abnormal cerebral circulations were visualized and quantified on both patients using the developed technique.

CONCLUSION

The vascular territorial imaging technique developed in this study allowed for the generation of territorial maps with user-defined level of details within a clinically feasible scan time, and as such may provide useful information to assess cerebral circulation balance in different pathologies.

Blood Pressure Management in Acute Ischemic Stroke

PURPOSE OF REVIEW

Abrupt blood pressure (BP) rise is the most common clinical symptom of acute ischemic stroke (AIS). However, BP alterations during AIS reflect many diverse mechanisms, both stroke-related and nonspecific epiphenomena, which change over time and across patients. While extremes of BP as well as high BP variability have been related with worse outcomes in observational studies, optimal BP management after AIS remains challenging.

RECENT FINDINGS

This review discusses the complexity of the factors linking BP changes to the clinical outcomes of patients with AIS, depending on the treatment strategy and local vessel status and, in particular, the degree of reperfusion achieved. The evidence for possible additional clinical markers, including the presence of arterial hypertension, and comorbid organ dysfunction in individuals with AIS, as informative and helpful factors in therapeutic decision-making concerning BP will be reviewed, as well as recent data on neurovascular monitoring targeting person-specific local cerebral perfusion and metabolic demand, instead of the global traditional parameters (BP among others) alone. The individualization of BP management protocols based on a complex evaluation of the homeostatic response to focal cerebral ischemia, including but not limited to BP changes, may be a valuable novel goal proposed in AIS, but further trials are warranted.

The impact of native leptomeningeal collateralization on rapid blood flow recruitment following ischemic stroke

The leptomeningeal collateral status is an independent predictor of stroke outcome. By means of optical coherent tomography angiography to compare two mouse strains with different extent of native leptomeningeal collateralization, we determined the spatiotemporal dynamics of collateral flow and downstream hemodynamics following ischemic stroke. A robust recruitment of leptomeningeal collateral flow was detected immediately after middle cerebral artery (MCA) occlusion in C57BL/6 mice, with continued expansion over the course of seven days. In contrast, little collateral recruitment was seen in Balb/C mice during- and one day after MCAO, which coincided with a greater infarct size and worse functional outcome compared to C57BL/6, despite a slight improvement of cortical perfusion seven days after MCAO. Both strains of mice experienced a reduction of blood flow in the penetrating arterioles (PA) by more than 90% 30-min after dMCAO, although the decrease of PA flow was greater and the recovery was less in the Balb/C mice. Further, Balb/C mice also displayed a prolonged greater heterogeneity of capillary transit time after dMCAO in the MCA territory compared to C57BL/6 mice. Our data suggest that the extent of native leptomeningeal collaterals affects downstream hemodynamics with a long lasting impact in the microvascular bed after cortical stroke.

Regional leptomeningeal collateral score by computed tomographic angiography correlates with 3-month clinical outcome in acute ischemic stroke

PURPOSE:

The aim of the study is to assess the correlation between regional leptomeningeal collateral (rLMC) Scores calculated on computed tomography (CT) angiography following acute anterior circulation ischemic stroke, with 3-month clinical outcome measured as modified Rankin Scale (mRS) and Barthel Index (BI).

MATERIALS AND METHODS:

A total of thirty patients were studied as per the exclusion and inclusion criteria and after informed consent. Multi-phase CT angiography was carried out within 24 h of stroke onset, and collateral scoring was done using rLMC score along with Alberta stroke programme early CT (ASPECT) scoring. At 3 months, patients were followed up to evaluate the clinical outcome using mRS and BI. Statistical analysis was performed to find out the correlation between rLMC score, ASPECT score, and clinical outcome and for association with demographic parameters and stroke risk factors.

RESULTS:

A strong correlation was noted between ASPECT and rLMC scores (P < 0.001) and between rLMC scores and clinical outcome at 3 months (mRS and BI). Correlation with mRS (P < 0.001) was nearly as strong as that of BI on follow-up (P < 0.001). The ASPECT score also was a predictor of clinical outcome and showed correlation with mRS (P < 0.001) and BI (P < 0.001). No significant association was found between various stroke risk factors and demographic parameters with rLMC scores. The rLMC scoring system showed substantial inter-rater reliability with Kappa = 0.7.

CONCLUSIONS:

rLMC score in CT angiography correlates with ASPECT Score and clinical outcome at 3 months. Hence, this scoring system can be used for collateral quantification as may be of use in predicting short-term clinical outcomes.

Utility of Leptomeningeal Collaterals in Predicting Intracranial Atherosclerosis-Related Large Vessel Occlusion in Endovascular Treatment

Earlier or preprocedural identification of occlusion pathomechanism is crucial for effective endovascular treatment. As leptomeningeal collaterals tend to develop well in chronic ischemic conditions such as intracranial atherosclerosis (ICAS), we investigated whether leptomeningeal collaterals can be a preprocedural marker of ICAS-related large vessel occlusion (ICAS-LVO) in endovascular treatment. A total of 226 patients who underwent endovascular treatment were retrospectively reviewed. We compared the pattern of leptomeningeal collaterals between patients with ICAS-LVO and without. Leptomeningeal collaterals were assessed by preprocedural computed tomography angiography (CTA) and basically categorized by three different collateral assessment methods. Better leptomeningeal collaterals were significantly associated with ICAS-LVO, although they were not independent for ICAS-LVO. When leptomeningeal collaterals were dichotomized to incomplete (<100%) and complete (100%), the latter was significantly more frequent in patients with ICAS-LVO (52.5% versus 20.4%) and remained an independent factor for ICAS-LVO (odds ratio, 3.32; 95% confidence interval, 1.52-7.26; p = 0.003). The area under the curve (AUC) value of complete leptomeningeal collateral supply was 0.660 for discrimination of ICAS-LVO. Incomplete leptomeningeal collateral supply was not likely ICAS-LVO, based on the high negative predictive value (88.6%). Considering its negative predictive value and the independent association between complete leptomeningeal collateral supply and ICAS-LVO, leptomeningeal collaterals could be helpful in the preprocedural determination of occlusion pathomechanism.

Computer Modeling of Clot Retrieval-Circle of Willis

Endovascular clot retrieval, often referred to as mechanical thrombectomy, has transformed the treatment of patients with ischemic stroke based on an underlying large cerebral vessel occlusion, ranging from the extracranial internal carotid artery (ICA) to the M1 (proximal) segment of the middle cerebral artery (MCA). The aim of this study was to evaluate the effect of a progressive occlusion of the extracranial portion of the ICA on the cerebral blood flow either with a conventional guiding catheter or a balloon-guiding catheter, which enables the operator to completely occlude the parent artery by inflating the balloon around the tip of this type of guiding catheter. We evaluated the impact of flow reduction in the ICA in the setting of ipsilateral MCA occlusion given the different configurations of the circle of Willis (CoW). The computer model of cerebral arteries was based on anatomical works by Rhoton (1) and van der Eecken (2). The interactive experimental results are available on the web at https://gntem3.shinyapps.io/ecrsim. In the setting of left MCA occlusion, compensation from the anterior and posterior communicating artery preserved the flow in the left anterior cerebral artery (ACA) but not the left MCA branches. Under selected CoW configurations, such as classic, missing Acom, or missing A1 segment of the ACA and concurrent right ICA occlusion, there was a progressive decrease of flow in the left ACA to a minimum of 78% when the simulated catheter fully occluded the left ICA. Flow collapsed (<10%) in the left ACA and MCA branches under CoW configurations, such as bilateral fetal PCA. In summary, compensatory flow collapsed under certain clot retrieval scenarios and unusual configurations of CoW.

Improved collateral flow and reduced damage after remote ischemic perconditioning during distal middle cerebral artery occlusion in aged rats

Circulation through cerebral collaterals can maintain tissue viability until reperfusion is achieved. However, collateral circulation is time limited, and failure of collaterals is accelerated in the aged. Remote ischemic perconditioning (RIPerC), which involves inducing a series of repetitive, transient peripheral cycles of ischemia and reperfusion at a site remote to the brain during cerebral ischemia, may be neuroprotective and can prevent collateral failure in young adult rats. Here, we demonstrate the efficacy of RIPerC to improve blood flow through collaterals in aged (16-18 months of age) Sprague Dawley rats during a distal middle cerebral artery occlusion. Laser speckle contrast imaging and two-photon laser scanning microscopy were used to directly measure flow through collateral connections to ischemic tissue. Consistent with studies in young adult rats, RIPerC enhanced collateral flow by preventing the stroke-induced narrowing of pial arterioles during ischemia. This improved flow was associated with reduced early ischemic damage in RIPerC treated aged rats relative to controls. Thus, RIPerC is an easily administered, non-invasive neuroprotective strategy that can improve penumbral blood flow via collaterals. Enhanced collateral flow supports further investigation as an adjuvant therapy to recanalization therapy and a protective treatment to maintain tissue viability prior to reperfusion.

Ablation of Vitamin D Signaling Compromises Cerebrovascular Adaptation to Carotid Artery Occlusion in Mice

Vitamin D insufficiency has been associated with increased incidence and severity of cerebrovascular disorders. We analyzed the impact of impaired vitamin D signaling on the anatomical and functional aspects of cerebrovascular adaptation to unilateral carotid artery occlusion (CAO), a common consequence of atherosclerosis and cause of ischemic stroke. Cerebrocortical blood flow (CoBF) showed a significantly increased drop and delayed recovery after CAO in mice carrying a functionally inactive vitamin D receptor (VDR) with the most sustained perfusion deficit in the temporal cortex. To identify the cause(s) for this altered adaptation, the extent of compensatory blood flow increase in the contralateral carotid artery and the morphology of pial collaterals between the anterior and middle cerebral arteries were determined. Whereas VDR deficiency had no significant influence on the contralateral carotid arterial blood flow increase, it was associated with decreased number and increased tortuosity of pial anastomoses resulting in unfavorable changes of the intracranial collateral circulation. These results indicate that VDR deficiency compromises the cerebrovascular adaptation to CAO with the most sustained consequences in the temporal cortex. The dysregulation can be attributed to the altered development and function of pial collateral circulation whereas extracranial vessels may not be impaired.

ACE (Angiotensin-Converting Enzyme) Inhibition Reverses Vasoconstriction and Impaired Dilation of Pial Collaterals in Chronic Hypertension

Leptomeningeal anastomoses (LMAs) are pial collaterals that perfuse the penumbra and important for stroke outcome. We previously showed LMAs from SHRs (spontaneously hypertensive rats) were vasoconstricted compared with normotensive Wistar rats. Here, we investigated mechanisms by which hypertension causes LMA vasoconstriction. SHRs were treated with the ACE (angiotensin-converting enzyme) inhibitor captopril, an Ang II (angiotensin II)-independent antihypertensive agent hydralazine, or vehicle for 5 weeks in drinking water (n=8/group). A group of Wistar rats (n=8) had regular drinking water served as controls. Blood pressure was measured twice weekly by tail-cuff. LMAs were isolated and studied under pressurized conditions. Vasoreactivity of LMAs, including myogenic responses, reactivity to Rho-kinase inhibitor Y-27632, and nitric oxide were measured. Both captopril and hydralazine lowered blood pressure in SHRs similar to Wistar. However, only captopril normalized LMA increased tone compared with untreated SHRs (15±2% versus 50±3%; P<0.01) that was similar to Wistar (16±2%) but not hydralazine (38±6%; P>0.05). Vasodilatory response of LMAs to Y-27632 was impaired in SHRs compared with Wistar (28±3% versus 81±4%; P<0.01) that was restored by captopril (84±5%; P<0.01) and partially hydralazine (59±4%). LMAs from all groups constricted similarly to NOS (NO synthase) inhibition; however, the vasodilatory response of LMAs to the nitric oxide donor sodium nitroprusside was impaired in SHRs compared with Wistar rats (29±4% versus 80±2%; P<0.01) that was restored by captopril (84±4%; P<0.01), not hydralazine (38±8%; P>0.05). These results suggest that ACE inhibition during chronic hypertension reversed vascular dysfunction and hyperconstriction of LMAs that could improve stroke outcome by increasing collateral perfusion.

Impact of stroke co-morbidities on cortical collateral flow following ischaemic stroke

Acute hyperglycaemia and chronic hypertension worsen stroke outcome but their impact on collateral perfusion, a determinant of penumbral life span, is poorly understood. Laser-speckle contrast imaging (LSCI) was used to determine the influence of these stroke comorbidities on cortical perfusion after permanent middle cerebral artery occlusion (pMCAO) in spontaneously hypertensive stroke prone rats (SHRSP) and normotensive Wistar rats. Four independent studies were conducted. In animals without pMCAO, cortical perfusion remained stable over 180 min. Following pMCAO, cortical perfusion was markedly reduced at 30 min then gradually increased, via cortical collaterals, over the subsequent 3.5 h. In the contralateral non-ischaemic hemisphere, perfusion did not change over time. Acute hyperglycaemia (in normotensive Wistar) and chronic hypertension (SHRSP) attenuated the restoration of cortical perfusion after pMCAO. Inhaled nitric oxide did not influence cortical perfusion in SHRSP following pMCAO. Thus, hyperglycaemia at the time of arterial occlusion or pre-existing hypertension impaired the dynamic recruitment of cortical collaterals after pMCAO. The impairment of collateral recruitment may contribute to the detrimental effects these comorbidities have on stroke outcome.

Impaired Collateral Flow in Pial Arterioles of Aged Rats During Ischemic Stroke

Cerebral collateral circulation and age are critical factors in determining outcome from acute ischemic stroke. Aging may lead to rarefaction of cerebral collaterals, and thereby accelerate ischemic injury by reducing penumbral blood flow. Dynamic changes in pial collaterals after onset of cerebral ischemia may vary with age but have not been extensively studied. Here, laser speckle contrast imaging (LSCI) and two-photon laser scanning microscopy (TPLSM) were combined to monitor cerebral pial collaterals between the anterior cerebral artery (ACA) and the middle cerebral artery (MCA) in young adult and aged male Sprague Dawley rats during distal middle cerebral artery occlusion (dMCAo). Histological analysis showed that aged rats had significantly greater volumes of ischemic damage than young rats. LSCI showed that cerebral collateral perfusion declined over time after stroke in aged and young rats, and that this decline was significantly greater in aged rats. TPLSM demonstrated that pial arterioles narrowed faster after dMCAo in aged rats compared to young adult rats. Notably, while arteriole vessel narrowing was comparable 4.5 h after ischemic onset in aged and young adult rats, red blood cell velocity was stable in young adults but declined over time in aged rats. Overall, red blood cell flux through pial arterioles was significantly reduced at all time-points after 90 min post-dMCAo in aged rats relative to young adult rats. Thus, collateral failure is more severe in aged rats with significantly impaired pial collateral dynamics (reduced diameter, red blood cell velocity, and red blood cell flux) relative to young adult rats.

Association of atherosclerotic plaque features with collateral circulation status in elderly patients with chronic carotid stenosis

OBJECTIVE

To determine the association of carotid plaque features with collateral circulation status in elderly patients with moderate to severe carotid stenosis.

METHODS

Elderly patients (> 60 years) with moderate to severe carotid stenosis were recruited and categorized into good and poor collateral circulation groups, and underwent magnetic resonance imaging and computed tomography imaging. The carotid plaque features including lipid-rich necrotic core, intraplaque hemorrhage, calcification, and fibrous cap rupture (FCR) were evaluated, and maximum wall thickness, normalized wall index (NWI), and luminal stenosis were measured. The association between these variables and collateral circulation status was analyzed.

RESULTS

Of the 97 patients (78 males, mean age: 69.0 ± 6.1 years), 19 (19.6%) had poor collaterals. The poor collateral group had a significantly higher NWI (93.7% ± 5.0% vs. 89.0% ± 7.9%, P = 0.011), a greater extent of stenosis (80.0% ± 11.4% vs. 75.3% ± 9.4%, P = 0.036) and FCR (84.2% vs. 55.1%, P = 0.020) compared with good collateral group. Carotid NWI (OR = 3.83, 95% CI: 1.36-10.82, P = 0.011) and more FCR (OR = 6.77, 95% CI: 1.35-33.85, P = 0.020) were associated with poor collateral circulation after adjustment for the confounding factors. The combination of NWI, FCR, systolic blood pressure, and triglycerides had the highest area-under-the-curve (AUC = 0.85) for detection of poor collaterals.

CONCLUSIONS

Carotid plaque features, specifically NWI and FCR, are independently associated with poor collateral circulation, and the combination of carotid plaque features and traditional risk factors has a stronger predictive value for poor collateral circulation than plaque features alone.

Resting-state Functional Magnetic Resonance Imaging Identifies Cerebrovascular Reactivity Impairment in Patients With Arterial Occlusive Diseases: A Pilot Study

BACKGROUND

The development of noninvasive approaches for identifying hypoperfused brain tissue at risk is of major interest. Recently, the temporal-shift (TS) maps estimated from resting-state blood oxygenation level-dependent (BOLD) signals have been proposed for determining hemodynamic state.

OBJECTIVE

To examine the equivalency of the TS map and the cerebrovascular reactivity (CVR) map derived from acetazolamide-challenged single-photon emission computed tomography (SPECT) in identifying hemodynamic impairment in patients with arterial occlusive diseases.

METHODS

Twenty-three patients with arterial occlusive diseases who underwent SPECT were studied. With a recursive TS analysis of low-frequency fluctuation of the BOLD signal, a TS map relative to the global signal was created for each patient. The voxel-by-voxel correlation coefficient was calculated to examine the image similarity between TS and SPECT-based cerebral blood flow (CBF) or CVR maps in each patient. Furthermore, simple linear regression analyses were performed to examine the quantitative relationship between the TS of BOLD signals and CVR in each cerebrovascular territory.

RESULTS

The within-patient, voxel-by-voxel comparison revealed that the TS map was more closely correlated with SPECT-CVR map ([Z(r)] = 0.42 ± 0.18) than SPECT-CBF map ([Z(r)] = 0.058 ± 0.11; P < .001, paired t-test). The regression analysis showed a significant linear association between the TS of BOLD signals and CVR in the anterior circulation where the reduction of CVR was evident in the patient group.

CONCLUSION

BOLD TS analysis has potential as a noninvasive alternative to current methods based on CVR for identification of tissue at risk of ischemic stroke.