Collateral Circulation in Ischemic Stroke: Assessment Tools and Therapeutic Strategies.

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Revascularization encompasses all treatment-related improvements in blood flow, including recanalization of the proximal arterial occlusion and reperfusion of the downstream territory. Recanalization is required for antegrade tissue reperfusion, but recanalization may not necessarily lead to reperfusion in regions where distal emboli or established infarctions are present.1,2 On the contrary, acute reperfusion without recanalization may occur in patients who received or did not received endovascular therapies, and reperfusion ≤6 hours was consistently superior to recanalization in predicting tissue and clinical outcome.3 The cerebral collateral circulation refers to the subsidiary network of vascular channels that stabilize cerebral blood flow when principal conduits fail. Collateral status differs among patients with acute ischemic stroke. Relatively sparse attention has been devoted to the role of baseline collateral circulation in patients with acute ischemic stroke who are candidates for revascularization. The Interventional Management of Stroke (IMS) III,4 Mechanical Retrieval and Recanalization of Stroke Clots Using Embolectomy (MR RESCUE),5 and Intra-Arterial Versus Systemic Thrombolysis for Acute Ischemic Stroke (SYNTHESIS EXP) trials6 were 3 multicenter, prospective, randomized controlled trials, which failed to show a benefit from endovascular intervention for acute ischemic stroke. In addition, successful recanalization failed to improve the functional outcome in a significant proportion of patients, ranging from 26% to 49% (futile and dangerous recanalization), stimulating the need to improve the selection of patients based on individual pathophysiology.7,8 Among neuroimaging parameters, a large core and poor collaterals are demonstrated to be strong predictors of both response to endovascular therapy and functional outcome,9–13 and excluding patients with large core and poor collateral circulation may improve the therapeutic benefit from endovascular therapy. In the subgroup analysis of the IMS III trial, more robust collateral grade was associated with better clinical outcomes.14 Adequate collateral circulation …