Review Article
Assessment of Arterial Collateralization and Its Relevance to Intra-arterial Therapy for Acute Ischemic Stroke

https://doi.org/10.1016/j.jstrokecerebrovasdis.2013.03.012Get rights and content

Evidence from recent randomized controlled studies comparing intra-arterial (IA) therapy with intravenous tissue plasminogen activator highlighted the mismatch between recanalization success and clinical outcomes in patients presenting with acute ischemic stroke. There is emerging interest in the impact of arterial collateralization, as determined by leptomeningeal anastomoses (LMAs), on the treatment outcomes of IA therapy. The system of LMA constitutes the secondary network of cerebral collateral circulation apart from the Circle of Willis. Both anatomic and angiographic studies confirmed significant interindividual variability in LMA. This review aims to outline the current understanding of arterial collateralization and its impact on outcomes after IA therapy for acute ischemic stroke, underpinning the possible role of arterial collateralization assessment as a selection tool for patients most likely to benefit from IA therapy.

Section snippets

Intravenous Thrombolysis

The guiding principle of acute stroke treatment is the timely recanalization of occluded arteries, leading to restoration of cerebral blood flow. Intravenous tissue plasminogen activator (IV-tPA) is shown to improve outcomes as shown by the National Institute of Neurological Disorders and Stroke trial and the Safe Implementation of Thrombolysis in Stroke Monitoring Study registry.1, 2, 3 Following the European Cooperative Acute Stroke Study III trial and pooled data from the large IV-tPA

Poor Clinical Outcomes Despite Good Recanalization

Although endovascular techniques have shown better recanalization rates than intravenous thrombolysis, this has not been matched by a corresponding improvement in clinical outcomes (Table 1). In the MultiMERCI trial, recanalization rate of 69.5% was achieved, but good clinical outcome remained 36% with a mortality rate of 34%.10 The Penumbra Pivotal Stroke trial demonstrated an 81.6% recanalization rate with only 25% positive clinical outcome.11

Several possible mechanisms have been put forward

Human

The development of the cerebral collateral circulatory channels during embryonic stages parallels development of the nervous system. At the fifth week of gestational age, 4 pairs of presegmental arteries originate from the primitive internal carotid artery (ICA): the trigeminal arteries, the otic arteries, the hypoglossal arteries, and the proatlantal intersegmental arteries. By the sixth gestational week, dorsal to the presegmental arteries, bilateral longitudinal neural arteries unite to form

Animal Model

The dynamics of collateral blood flow during ischemic stroke remain little known owing to heterogeneity in patient demographics and treatment options despite of the advent of medical technology imaging. Animal model studies offer greater experimental control and facilitate an understanding of collateral vascular dynamics. Early studies in animal models showed that the pyriform branch of the MCA has collateral communication with the ACA and that the parietal and temporal branches collateralize

Conclusions

There is accumulating evidence that clinical outcomes after IA therapy is critically dependant on arterial collateralization. However, the prognostic role of collateralization has not been definitively established given the lack of a uniform grading system consequent of poorly defined parameters and individual variability in the Circle of Willis. Notwithstanding advances in the imaging of collateral circulation, its validity requires standardization in assessment methods. Further trials are

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