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Introduction: The CT Perfusion (CTP) parameter Time-Maximum greater than 6 seconds (Tm > 6s) represents delayed blood flow in critically hypoperfused brain tissue. Though Tm > 6s is expected to accurately represent infarct size in stroke patients who do not undergo revascularization, some brain tissue at risk may not progress to infarction and recover spontaneously (“benign oligemia”). We sought to investigate the relationship between Tm > 6s and the gold standard of final infarct volume on DWI MRI in patients with anterior circulation, large artery occlusion (LAO) acute ischemic stroke (AIS) who do not achieve reperfusion.Hypothesis: Critically hypoperfused brain tissue, as represented by CTP Tm > 6s, overestimates final infarct volume on DWI MRI in at least 50% of patients with ICA or proximal MCA occlusions without angiographic revascularization.Methods: From a large healthcare system’s stroke network database, we conducted a retrospective analysis comparing delayed perfusion volume (Tm > 6s; RAPID iSchemaView) on CTP and DWI MRI volume (ADC < 620cc; RAPID iSchemaView) in patients with ICA, M1, or M2 occlusions between November 2016 and June 2017 not treated with acute reperfusion therapy, or without angiographic revascularization (TICI 0).Results: Over an 8-month period, 19 cases were identified with baseline CTP, follow-up MRI, and no reperfusion of an ICA, M1, or M2 occlusion. Mean age was 65.8 years old and median NIHSS was 8. Mean duration from last known well time to CTP and MRI was 4.4 and 22.8 hours, respectively. Three patients were treated with IV TPA and endovascular therapy, 4 received only endovascular therapy, and 12 did not receive IV TPA nor endovascular intervention. The Tm >6s volume was greater than follow-up DWI MRI volume in 13/19 (68%) cases by an average of 37.4cc.Conclusions: Critically hypoperfused brain tissue on CTP, represented by Tm > 6s, may spontaneously recover in patients with proximal, LAO AIS. Establishing CTP parameters that delineate ischemic penumbra from benign oligemia will aid in identifying the volume of ischemic tissue truly at risk for infarction in LAO patients.