Collateral blood vessels in acute ischemic stroke: a physiological window to predict future outcomes

Evolucollateral dynamics in stroke: Evolutionary pathophysiology, remodelling and emerging therapeutic strategies

Leptomeningeal collaterals (LMCs) are crucial in mitigating the impact of acute ischemic stroke (AIS) by providing alternate blood flow routes when primary arteries are obstructed. This article explores the evolutionary pathophysiology of LMCs, highlighting their critical function in stroke and the genetic and molecular mechanisms governing their development and remodelling. We address the translational challenges of applying animal model findings to human clinical scenarios, emphasizing the need for further research to validate emerging therapies-such as pharmacological agents, gene therapy and mechanical interventions-in clinical settings, aimed at enhancing collateral perfusion. Computational modelling emerges as a promising method for integrating experimental data, which requires precise parameterization and empirical validation. We introduce the 'Evolucollateral Dynamics' hypothesis, proposing a novel framework that incorporates evolutionary biology principles into therapeutic strategies, offering new perspectives on enhancing collateral circulation. This hypothesis emphasizes the role of genetic predispositions and environmental influences on collateral circulation, which may impact therapeutic strategies and optimize treatment outcomes. Future research must incorporate human clinical data to create robust treatment protocols, thereby maximizing the therapeutic potential of LMCs and improving outcomes for stroke patients.

The Pathophysiology of Collateral Circulation in Acute Ischemic Stroke

Cerebral collateral circulation is a network of blood vessels which stabilizes blood flow and maintains cerebral perfusion whenever the main arteries fail to provide an adequate blood supply, as happens in ischemic stroke. These arterial networks are able to divert blood flow to hypoperfused cerebral areas. The extent of the collateral circulation determines the volume of the salvageable tissue, the so-called "penumbra". Clinically, this is associated with greater efficacy of reperfusion therapies (thrombolysis and thrombectomy) in terms of better short- and long-term functional outcomes, lower incidence of hemorrhagic transformation and of malignant oedema, and smaller cerebral infarctions. Recent advancements in brain imaging techniques (CT and MRI) allow us to study these anastomotic networks in detail and increase the likelihood of making effective therapeutic choices. In this narrative review we will investigate the pathophysiology, the clinical aspects, and the possible diagnostic and therapeutic role of collateral circulation in acute ischemic stroke.

MRI for collateral assessment pre-thrombectomy and association with outcome: a systematic review and meta-analysis

PURPOSE

Various neuroimaging methods exist to assess the collateral circulation in stroke patients but much of the evidence is based on computed tomography. Our aim was to review the evidence for using magnetic resonance imaging for collateral status evaluation pre-thrombectomy and assess the impact of these methods on functional independence.

METHODS

We systematically reviewed EMBASE and MEDLINE for studies that evaluated baseline collaterals using MRI pre-thrombectomy and conducted a meta-analysis to express the relationship between good collaterals (defined variably as the presence [good] vs absence [poor] or quality [ordinal scores binarized as good-moderate vs poor] of collaterals) and functional independence (modified Rankin score mRS≤2) at 90 days. Outcome data were presented as relative risk (RR, 95% confidence interval, 95%CI). We assessed for study heterogeneity, publication bias, and conducted subgroup analyses of different MRI methods and affected arterial territories.

RESULTS

From 497 studies identified, we included 24 (1957 patients) for the qualitative synthesis, and 6 (479 patients) for the metanalysis. Good pre-thrombectomy collaterals were significantly associated with favorable outcome at 90 days (RR=1.91, 95%CI=1.36-2.68], p= 0.0002) with no difference between MRI methods and affected arterial territory subgroups. There was no evidence of statistical heterogeneity (I2=25%) among studies but there was evidence of publication bias.

CONCLUSION

In stroke patients treated with thrombectomy, good pre-treatment collaterals assessed using MRI are associated with double the rate of functional independence. However, we found evidence that relevant MR methods are heterogenous and under-reported. Greater standardization and clinical validation of MRI for collateral evaluation pre-thrombectomy are required.

Recurrent stroke syndrome without abnormality on magnetic resonance imaging caused by stenosis of middle cerebral artery: A case report

Middle cerebral artery stenosis is the leading and the most frequent cause of stroke due to intracranial stenosis in Asia. Magnetic resonance imaging (MRI) is more sensitive than computed tomography of the head for detecting acute brain ischemia. We are reporting a case of a 28-year-old female with recurrent left hemiparesis. After the last attack, an improvement in motor function was seen in less than 24 hours. Though the restoration of motor functions is not complete yet, an MRI scan that was done two weeks later appeared normal. Ischemic stroke in middle cerebral artery stenosis is associated with hemodynamic stroke due to hypoperfusion or lack of blood flow to brain tissue. Recurrent strokes can be prevented by better medical management in patients through regulation and management of risk factors.

The Overexpression of Sonic Hedgehog Associates with Collateral Development and Amelioration of Oxidative Stress in Stroke Patients

PURPOSE

Sonic hedgehog (SHH) signaling pathway in oxidative stress condition has been acknowledged as a key trigger for angiogenesis and collateral vessel growth in the ischemic brain, and it exerts a protective effect on neuronal cells during oxidative stress.

METHODS

A total of sixty patients (n = 30 good collateral profile and n = 30 poor collateral profile) diagnosed with acute cerebral ischemia were enrolled in this study. qRT-PCR was performed to analyze the expression levels of SHH, Gli1, and superoxide dismutase (SOD), genes. Also, the serum levels of oxidative stress markers were determined in experimental groups.

RESULTS

The expression levels of SHH and Gli1 genes were significantly (p < 0.05) higher in stroke patients with good collateral circulation compared with those with poor collateral circulation, while SOD gene expression was similar between two groups (p > 0.05). A significantly positive correlation was found between the gene expression of SHH and Gli1 (r = 0.604, p < 0.001), SOD and Gli1 (r = 0.372, p < 0.003) genes. Our findings showed that the serum level of total antioxidant capacity (TAC) and Glutathione (GSH) and SOD enzyme activity was significantly (p < 0.05) increased, while serum total oxidant status (TOS) and malondialdehyde (MDA) levels were significantly (p < 0.05) decreased in patients with good collateral circulation as compared with those with poor collateral circulation.

CONCLUSION

Our observations shed light on the association of the SHH/Gli1 signaling pathway with cerebral collateral vessel development following ischemia. Oxidative stress in stroke patients with poor collateral circulation may result in the overexpression of SHH/Gli1 signaling pathway which possibly contribute to oxidative stress attenuation, as well as modulate angiogenesis and collateral vessels development.

Intracranial collateral circulation and its role in neurovascular pathology

Background

Collateral circulation is a vascular network which maintains the blood flow after the partial blockage of primary vascular pathways. This acts as potential vascular supplementary system and plays important role in the cerebral ischemia.

Main body

Collateral circulation has implications in the management especially related to cerebral endovascular treatment and thrombolytic therapy. It is considered as subsidiary network of vascular channels, which is highly variable. Insufficient arterial supply is due to the hemodynamic compromise because of thromboembolism. Apart from the collaterals, there is additional existence of a group of vessels known as venous collaterals. Their function is variable and they contribute to the augmentation of venous drainage in venous ischemias. Various pharmacological interventions are used to modulate the collaterals, these can prove to be a complementary alternative to the invasive intracerebral interventions.

Conclusions

The aim of this review article is to highlight the importance of cerebral collateral circulation and to discuss the various available pharmacological alternatives available and their current relevance in the management of various neurovascular pathologies.

Cerebrovascular Reactivity: Purpose, Optimizing Methods, and Limitations to Interpretation - A Personal 20-Year Odyssey of (Re)searching

The brain is a neurovascular organ. A stimulus-response approach is effective in interrogating the physiology of its vasculature. Ideally, the stimulus is standardized across patients, and in a single patient over time. We developed a standard stimulus and attempted to measure, classify, and interpret the many forms of responses. Over the past 20 years, our work has delivered nuanced insights into normal cerebral vascular physiology, as well as adaptive physiological responses in the presence of disease. The trajectory of our understanding did not follow a logical linear progression; rather, it emerged as a coalescence of new, old, and previously dismissed, ideas that had accumulated over time. In this essay, we review what we believe were our most valuable - and sometimes controversial insights during our two decades-long journey.

Presence of an Anterior Communicating Artery as a Prognostic Factor in Revascularization for Anterior Circulation Acute Ischemic Stroke

BACKGROUND

No reports have evaluated collateral circulation using simpler measures involving magnetic resonance imaging. Because an anterior communicating artery (A-com) is important in collateral circulation, we investigated whether the presence of an A-com affected the clinical revascularization outcomes in acute ischemic stroke (AIS) in the anterior circulation.

METHODS

The present retrospective study included 73 patients who had undergone continuous administration of recombinant tissue plasminogen activator and revascularization for AIS in the anterior circulation from April 2014 to September 2018. The presence of an A-com was evaluated using preoperative time-of-flight magnetic resonance angiography. The patient characteristics and clinical outcomes were compared, and we investigated the influence of the presence or absence of an A-com on these clinical outcomes. The clinical outcomes were analyzed using multiple logistic regression.

RESULTS

The clinical outcomes did not significantly correlate with age, sex, or occlusion location but did significantly correlate with the preoperative National Institute of Health stroke scale score, diffusion-weighted Alberta Stroke Program early computed tomography score, reperfusion >50% (thrombolysis in cerebral infarction grade >2b), and onset to recanalization time. The presence of an A-com correlated significantly with good clinical outcomes (modified Rankin scale score 0-3; P = 0.0081) and reduced mortality (P = 0.03). Multiple logistic regression predicted for significantly good clinical outcomes with the presence of an A-com (odds ratio, 17.03; 95% confidence interval, 1.85-157.10; P = 0.012).

CONCLUSIONS

The presence of an A-com on preoperative time-of-flight magnetic resonance angiography is a good prognostic factor for revascularization in patients with anterior circulation AIS, confirms collateral circulation, and allows for faster and safer endovascular treatment.

Timely Visualization of the Collaterals Formed during Acute Ischemic Stroke with Fe3 O4 Nanoparticle-based MR Imaging Probe

Ischemic stroke is one of the major leading causes for long-term disability and mortality. Collateral vessels provide an alternative pathway to protect the brain against ischemic injury after arterial occlusion. Aiming at visualizing the collaterals occurring during acute ischemic stroke, an integrin α_v β₃ -specific Fe₃ O₄ -Arg-Gly-Asp (RGD) nanoprobe is prepared for magnetic resonance imaging (MRI) of the collaterals. Rat models are constructed by occluding the middle cerebral artery for imaging studies of cerebral ischemia and ischemia-reperfusion on 7.0 Tesla MRI using susceptibility-weighted imaging sequence. To show the binding specificity to the collaterals, the imaging results acquired with the Fe₃ O₄ -RGD nanoprobe and the Fe₃ O₄ mother nanoparticles, respectively, are carefully compared. In addition, an RGD blocking experiment is also carried out to support the excellent binding specificity of the Fe₃ O₄ -RGD nanoprobe. Following the above experiments, cerebral ischemia-reperfusion studies show the collateral dynamics upon reperfusion, which is very important for the prognosis of various revascularization therapies in the clinic. The current study has, for the first time, enabled the direct observation of collaterals in a quasi-real time fashion and further disclosed that the antegrade flow upon reperfusion dominates the blood supply of primary ischemic tissue during the early stage of infarction, which is significantly meaningful for clinical treatment of stroke.

Importance of Collateralization in Patients With Large Artery Intracranial Occlusive Disease: Long-Term Longitudinal Assessment of Cerebral Hemodynamic Function

Patients with large artery intracranial occlusive disease (LAICOD) are at risk for both acute ischemia and chronic hypoperfusion. Collateral circulation plays an important role in prognosis, and imaging plays an essential role in diagnosis, treatment planning, and prognosis of patients with LAICOD. In addition to standard structural imaging, assessment of cerebral hemodynamic function is important to determine the adequacy of collateral supply. Among the currently available methods of assessment of cerebral hemodynamic function, measurement of cerebrovascular reactivity (CVR) using blood oxygen level-dependent (BOLD) MRI and precisely controlled CO₂ has shown to be a safe, reliable, reproducible, and clinically useful method for long-term assessment of patients. Here, we report a case of long-term follow-up in a 28-year-old Caucasian female presented to the neurology clinic with a history of TIAs and LAICOD of the right middle cerebral artery (MCA). Initial structural MRI showed a right MCA stenosis and a small right coronal radiate lacunar infarct. Her CVR study showed a large area of impaired CVR with a paradoxical decrease in BOLD signal with hypercapnia involving the right MCA territory indicating intracerebral steal. The patient was managed medically with anticoagulant and antiplatelet therapy and was followed-up for over 9 years with both structural and functional imaging. Cortical thickness (CT) measures were longitudinally assessed from a region of interest that was applied to subsequent time points in the cortical region exhibiting steal physiology and in the same region of the contralateral healthy hemisphere. In the long-term follow-up, the patient exhibited improvement in her CVR as demonstrated by the development of collaterals with negligible changes to CT. Management of patients with LAICOD remains challenging since no revascularization strategies have shown efficacy except in patients with moyamoya disease. Management is well defined for acute ischemia where the presence and the adequacy of the collateralization dictate the need for intervention. Long-term assessment in neurovascular uncoupling (i.e., chronic ischemia) may reveal improvements in CVR as the durability of compensatory collaterals improve, even in cases with no intervention. Thus, assessment of cerebrovascular hemodynamics using CVR measurements coupled with time-of-flight MR angiography can be useful in the clinical management of patients with LAICOD.

The ratio between cerebral blood flow and Tmax predicts the quality of collaterals in acute ischemic stroke

Background

In acute ischemic stroke the status of collateral circulation is a critical factor in determining outcome. We propose a less invasive alternative to digital subtraction angiography for evaluating collaterals based on dynamic-susceptibility contrast magnetic resonance imaging.

Methods

Perfusion maps of Tmax and cerebral blood flow (CBF) were created for 35 patients with baseline occlusion of a major cerebral artery. Volumes of hypoperfusion were defined as having a Tmax delay of > 4 seconds (Tmax4s) and > 6 seconds (Tmax6s) and a CBF drop below 80% of healthy, contralateral tissue. For each patient a ratio between the volume of the CBF and the Tmax based perfusion deficit was calculated. Associations with collateral status and radiological outcome were assessed with the Mann-Whitney-U test, uni- and multivariable logistic regression analyses as well as area under the receiver-operator-characteristic (ROC) curve.

Results

The CBF/Tmax volume ratios were significantly associated with bad collateral status in crude logistic regression analysis as well as with adjustment for NIHSS at admission and baseline infarct volume (OR = 2.5 95% CI[1.2–5.4] p = 0.020 for CBF/Tmax 4s volume ratio and OR = 1.6 95% CI[1.0–2.6] p = 0.031 for CBF/Tmax6s volume ratio). Moreover, the ratios were significantly correlated to final infarct size (Spearman’s rho = 0.711 and 0.619, respectively for the CBF/Tmax4s volume ratio and CBF/Tmax6s volume ration, all p<0.001). The ratios also had a high area under the ROC curve of 0.93 95%CI[0.86–1.00]) and 0.90 95%CI[0.80–1.00]respectively for predicting poor radiological outcome.

Conclusions

In the setting of acute ischemic stroke the CBF/Tmax volume ratio can be used to differentiate between good and insufficient collateral circulation without the need for invasive procedures like conventional angiography.

Recanalisation therapy in patients with acute ischaemic stroke caused by large artery occlusion: choice of therapeutic strategy according to underlying aetiological mechanism?

Various mechanisms underlie causative large artery occlusion (LAO) in patients with acute ischaemic stroke. Cardioembolic and atherosclerotic occlusions are the two most common types. The pathophysiological changes and responses to mechanical thrombectomy (MT) and antithrombotic treatments including thrombolysis, antiplatelet and anticoagulation therapy may vary among patients with different aetiological mechanisms of occlusion. Atherosclerotic occlusion is inclined to have relatively abundant collaterals and larger area of penumbra, hence a relatively wider time window for reperfusion therapy, while poor response to medical thrombolysis and MT. Severe residual stenosis and reocclusion occurred frequently after MT in atherosclerotic LAO. Angioplasty and stenting as rescue or the first-line therapy and more intensified antiplatelet therapy beyond related recommendations in the current guidelines are sometimes used in managing acute causative LAO because of poor recanalisation after recommended standard thrombolysis or MT therapy, which are usually based on individual experience. Standard protocol to establish emergent aetiological diagnosis of causative LAO and individualised aetiology-specific treatment strategy is needed.

Collateral blood flow in different cerebrovascular hierarchy provides endogenous protection in cerebral ischemia

Collateral blood flow as vascular adaptions to focal cerebral ischemia is well recognized. However, few studies directly investigate the dynamics of collateral vessel recruitment in vivo and little is known about the effect of collateral blood flow in different cerebrovascular hierarchy on the neuropathology after focal ischemic stroke. Here, we report that collateral blood flow is critically involved in blood vessel compensations following regional ischemia. We occluded a pial arteriole using femtosecond laser ablating under the intact thinned skull and documented the changes of collateral flow around the surface communication network and between the surface communication network and subsurface microcirculation network using in vivo two photon microscopy imaging. Occlusion of the pial arteriole apparently increased the diameter and collateral blood flow of its leptomeningeal anastomoses, which significantly reduced the cortical infarction size. This result suggests that the collateral flow via surface communicating network connected with leptomeningeal anastomoses could greatly impact on the extent of infarction. We then further occluded the target pial arteriole and all of its leptomeningeal anastomoses. Notably, this type of occlusion led to reversals of blood flow in the penetrating arterioles mainly proximal to the occluded pial arteriole in a direction from the subsurface microcirculation network to surface arterioles. Interesting, the cell death in the area of ischemic penumbra was accelerated when we performed occlusion to cease the reversed blood flow in those penetrating arterioles, suggesting that the collateral blood flow from subsurface microcirculation network exerts protective roles in delaying cell death in the ischemic penumbra. In conclusion, we provide the first experimental evidence that collateral blood vessels at different cerebrovascular hierarchy are endogenously compensatory mechanisms in brain ischemia.

Clinical Outcome Predicted by Collaterals Depends on Technical Success of Mechanical Thrombectomy in Middle Cerebral Artery Occlusion

BACKGROUND

This study aimed to analyze the effects of technical outcome of mechanical thrombectomy (MTE) on the associations between collateral status, assessed with pretreatment computed tomography angiography (CTA), and neurological and functional outcome, as well as associations between collaterals and metabolic risk factors (arterial hypertension, diabetes, hyperlipidemia, overweight).

METHODS

Prospectively collected data of 115 patients with CTA-proven isolated middle cerebral artery occlusion treated successfully with MTE (Thrombosis in Cerebral Infarction [TICI] scale 2b or 3) were assessed retrospectively. Initial CTAs were assessed for the regional leptomeningeal collateralization score (rLMC), neurological status was determined with the National Institutes of Health Stroke Scale (NIHSS) at admission and discharge, and mid-term functional outcome was assessed using the modified Rankin scale (mRS) 90 days after MTE.

RESULTS

NIHSS score at admission was significantly associated with rLMC (P = .004), whereas rLMC and NIHSS at discharge showed no significant associations (P = .12). Better rLMC was significantly associated with improved mid-term mRS (P = .018). This association was even more significant after complete MTE (TICI 3; P = .011). Arterial hypertension was significantly more often found in patients with poor rLMC (0-10) than in patients with good rLMC (11-20; P = .046), yet other risk factors showed no significant associations (P > .05).

CONCLUSIONS

In patients with successful MTE, good collaterals were associated with better neurological status at admission and favorable mid-term functional outcome. In patients with complete MTE, associations were even more significant compared with those with "almost complete" MTE, suggesting a synergistic effect between good collaterals and complete MTE and a predictive value of collaterals for estimation of the potential clinical benefit of MTE.

Increased susceptibility of asymmetrically prominent cortical veins correlates with misery perfusion in patients with occlusion of the middle cerebral artery

OBJECTIVES

To evaluate tissue perfusion and venous susceptibility in ischaemic stroke patients as a means to predict clinical status and early prognosis.

METHODS

A retrospective study of 51 ischaemic stroke patients were enrolled in this study. Susceptibility, perfusion and National Institute of Health stroke scale (NIHSS) were compared between patients with and without asymmetrically prominent cortical veins (APCVs). The correlation between susceptibility, perfusion and NIHSS was performed.

RESULTS

Compared to patients without APCVs, the age of patients with APCVs was statistically older (p = 0.017). Patients with APCVs at discharge showed clinical deterioration in their NIHSS. Mean transit time (MTT), time to peak (TTP) and cerebral blood flow (CBF) in the stroke hemisphere were statistically delayed/decreased in patients with and without APCVs (all p < 0.05). In patients with APCVs, the changes in susceptibility positively correlated with increases in MTT and TTP (p < 0.05). Susceptibility and TTP positively correlated and CBF negatively correlated with NIHSS both at admission and discharge (p < 0.05).

CONCLUSIONS

Patients with APCVs have a tendency of deterioration. The presence of APCVs indicates the tissue has increased oxygen extraction fraction. Increased susceptibility from APCVs positively correlated with the delayed MTT and TTP, which reflects the clinical status at admission and predicts an early prognosis.

KEY POINTS

• Patients with and without APCVs have similar misery perfusion. • Patients with APCVs have a tendency of deterioration compared to those without. • The presence of APCVs indicated the tissue has increased oxygen extraction fraction. • Increased susceptibility from APCVs positively correlated with the MTT and TTP. • Increased susceptibility from APCVs reflected the clinical status at admission.