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Background and purpose Hemorrhagic transformation (HT) is a complication of stroke that can occur spontaneously or after treatment. We aimed to assess the inter- and intrarater reliability of HT diagnosis. Methods Studies assessing the reliability of the European Cooperative Acute Stroke Study (ECASS) classification of HT or of the presence (yes/no) of HT were systematically reviewed. A total of 18 raters independently examined 30 post-thrombectomy computed tomography scans selected from the Aspiration versus STEnt-Retriever (ASTER) trial. They were asked whether there was HT (yes/no), what the ECASS classification of the particular scan (0/HI1/HI2/PH1/PH2) (HI indicates hemorrhagic infarctions and PH indicates parenchymal hematomas) was and whether they would prescribe an antiplatelet agent if it was otherwise indicated. Agreement was measured with Fleiss' and Cohen's κ statistics. Results The systematic review yielded four studies involving few (≤3) raters with heterogeneous results. In our 18-rater study, agreement for the presence of HT was moderate [κ = 0.55; 95% confidence interval (CI), 0.41-0.68]. Agreement for ECASS classification was only fair for all five categories, but agreement improved to substantial (κ = 0.72; 95% CI, 0.69-0.75) after dichotomizing the ECASS classification into 0/HI1/HI2/PH1 versus PH2. The inter-rater agreement for the decision to reintroduce antiplatelet therapy was moderate for all raters, but substantial among vascular neurologists (κ = 0.70; 95% CI, 0.57-0.84). Conclusion The ECASS classification may involve too many categories and the diagnosis of HT may not be easily replicable, except in the presence of a large parenchymal hematoma.

Background Hemorrhagic transformation (HT) is a complication of stroke [1] that can occur spontaneously or after treatment. We aimed to assess the interrater and intrarater reliability of HT diagnosis. Methods Studies assessing the reliability of the European Cooperative Acute Stroke Study (ECASS) classification [2] of HT or of the presence (yes/no) of HT were systematically reviewed. Eighteen raters independently examined 30 post-thrombectomy [3] computed tomography scans selected from the Aspiration versus Stentriever (ASTER) trial [4] . They were asked whether there was HT (yes/no), what the ECASS classification of the particular scan (0/HI1/HI2/PH1/PH2) was, and whether they would prescribe an antiplatelet agent if it was otherwise indicated. Agreement [5] was measured with Fleiss’ and Cohen's kappa statistics. Results The systematic review yielded 4 studies involving few (≤ 3) raters with heterogeneous results. In our 18-rater study, agreement for the presence of HT was moderate (κ=0.55, 95%CI [0.41–0.68]). Agreement for ECASS classification was only fair for all 5 categories, but agreement improved to substantial (k = 0.72, 95%CI [0.69-0.75]) after dichotomizing ECASS into 0/HI1/HI2/PH1 versus PH2. The interrater agreement for the decision to reintroduce antiplatelet therapy was moderate for all raters, but substantial among vascular neurologists (κ=0.70 [0.57–0.84]). Conclusion The ECASS classification may involve too many categories and the diagnosis of HT may not be easily replicable, except in the presence of a large parenchymal hematoma. Clinical Trial Registration URL: http://www.clinicaltrials.gov Unique identifier: NCT02523261 .