It has long been apparent that the outcomes of all ischemic stroke patients are not alike, even those with remarkably similar occlusions found on vessel imaging who arrive in a similar time frame and receive similar care. “Good collaterals” are often pinpointed as a major factor that could cause these differences, however methods of effectively gauging collaterals have historically been time consuming or not available or possible in the acute setting. In their current article, authors Cortijo et al find that CT perfusion studies, specifically a calculated relative CBV (rCBV) may be an effective indicator of collateral flow, and thus may be useful in directing therapy in the acute setting.
From 2009 to 2012, 68 patients were enrolled. All participants had to have an MCA–territory stoke, vessel imaging, a CT perfusion (CTP), and IV tPA therapy. TCDs were used to measure recanalization of occluded vessels after treatment. CT perfusion source imaging (CTP-SI) was used to score collateral flow, with values of 0-1 graded “poor” (<50% filling) and 2-3 graded “good” (>50%). rCBV was calculated by comparing the CBV of the affected hemisphere to the unaffected side. Collateral score was significantly associated with mean rCBV (p<0.001), with ROC curve-derived best cutoff values between good and poor collaterals found to be 0.93 (sens 70%, spec 87%). While none of the patients with a low rCBV (<0.93) had a good 90 day outcome in the absence of early MCA recanalization, 52.9% of the patients with high rCBV (>0.93, thus indication of “good” collaterals) became functionally independent despite having a persistent MCA occlusion 2 hours after tPA-bolus.
Studies such as IMS-3 and MR-RESCUE have made a strong case that further delineation of ideal patient populations may be necessary to optimize outcomes post-stroke with intervention beyond IV-tPA. While this study has it’s limitations, such as a small sample size, it is promising that imaging modalities that are relatively fast and accessible like CTP may give us quick insight into the potential “durability” of a stroke bed, and thus give us some guidance as to whether intervention beyond IV tPA may be indicted.