1. An increased relative cerebral blood volume (rCBV) on perfusion-weighted magnetic resonance imaging prior to intravenous t-PA thrombolysis in acute ischemic stroke may indicate good collateral flow, a predictor of early vascular recanalization following treatment.
Evidence Rating Level: 2 (Good)
Study Rundown: Perfusion-weighted imaging (PWI) is commonly employed in the evaluation of acute ischemic stroke to delineate the penumbral region, or potentially recoverable but at-risk tissue following the ischemic insult. With early recanalization of the occluded vessel following intravenous t-PA administration, clinical outcomes are generally improved. However, in patients with poor collateral flow to the affected region, the availability of IV t-PA at the affected site may be minimized, reducing the chance of successful recanalization. In many patients, the chance of success is difficult to predict, and direct angiographic evaluation of the vessel following treatment is often unfeasible. However, magnetic resonance (MR)-based perfusion imaging may be a suitable approach to evaluate collateral flow, allowing stratification of patients based on their likelihood of successful early recanalization by IV t-PA. In the current study, the rCBV ratio on PWI before the administration of intravenous therapy was compared between patients with successful early recanalization versus delayed or failed recanalization, as determined by digital subtraction angiography (DSA). Among those patients with early restoration of flow, the rCBV ratio was significantly increased, indicating that the rCBV value may itself be indicative of high collateral perfusion to the ischemic region, subsequently predicting early recanalization. This study was limited by numerous factors, including an early recanalization rate following IV t-PA that is less than half the reported rate among acute ischemic stroke patients, a small sample size, and the biases inherent to retrospective studies. Future, larger-scale prospective trials examining the predictive value of PWI in determining the likelihood of recanalization may be valuable in selecting the appropriate reperfusion therapy for a given individual presenting with ischemic stroke.
In-Depth [retrospective cohort]: Eighty-five patients were retrospectively selected on the basis of acute middle cerebral artery ischemic stroke with initial evaluation by MR angiography with PWI and subsequent treatment with IV t-PA. Among these patients, all underwent digital subtraction angiography to evaluate if early recanalization had occurred. Sixteen patients (18.8%) displayed successful early recanalization without further treatment, while 52 of the remaining 69 patients underwent either intra-arterial chemical thrombolysis or mechanical thrombectomy. The rCBV ratio in patients with successful early recanalization was 1.01 ± 0.21 as compared to 0.82 ± 0.18 in those patients without successful recanalization (P < 0.01) and was determined to be an independent predictor of early recanalization (OR 1.07; Cl95% 1.02-1.12) alongside atrial fibrillation and serum glucose level. Those patients who did experience early recanalization were also significantly more likely to show a superior clinical outcome at 90 days as assessed by a modified Rankin Score of 0-1 (P < 0.01).
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