Original article Intracranial thrombus extent predicts clinical outcome, final infarct size and hemorrhagic transformation in ischemic stroke: the clot burden score Volker Puetz Ã1,2 , Imanuel Dzialowski 1,2 , Michael D. Hill 1,3 , Suresh Subramaniam 1 , P.N. Sylaja 1,4 , Andrea Krol 5 , Christine O’Reilly 5 , Mark E. Hudon 1 , William Y. Hu 1 , Shelagh B. Coutts 1 , Philip A. Barber 1 , Timothy Watson 1 , Jayanta Roy 1,6 , Andrew M. Demchuk 1 , for the Calgary CTA Study Group Background In ischemic stroke, functional outcomes vary depending on site of intracranial occlusion. We tested the prognostic value of a semiquantitative computed tomo- graphy angiography-based clot burden score. Methods Clot burden score allots major anterior circulation arteries 10 points for presence of contrast opacification on computed tomography angiography. Two points each are subtracted for thrombus preventing contrast opacification in the proximal M1, distal M1 or supraclinoid internal carotid artery and one point each for M2 branches, A1 and infra- clinoid internal carotid artery. We retrospectively studied patients with disabling neurological deficits (National Insti- tute of Health Stroke Scale score Z5) and computed tomo- graphy angiography within 24-hours from symptom onset. We analyzed percentages independent functional outcome (modified Rankin Scale score r2), final infarct Alberta Stroke Program Early Computed Tomography Score and paren- chymal hematoma rates across categorized clot burden score groups and performed multivariable analysis. Results We identified 263 patients (median age 73-years, National Institute of Health Stroke Scale score 10, onset- to-computed tomography angiography time 165 min). Clot burden scoreo10 was associated with reduced odds of independent functional outcome (odds ratio 0Á09 for clot burden scorer5; odds ratio 0Á22 for clot burden score 6–7; odds ratio 0Á48 for clot burden score 8–9; all versus clot burden score 10; Po0Á02 for all). Lower clot burden scores were associated with lower follow-up Alberta Stroke Program Early CT Scores (Po0Á001) and higher parenchymal hematoma rates (P 5 0Á008). Inter-rater reliability for clot burden score was 0Á87 (lower 95% confidence interval 0Á71) and intra-rater reliability 0Á96 (lower 95% confidence interval 0Á92). Conclusion The quantification of intracranial thrombus extent with the clot burden score predicts functional out- come, final infarct size and parenchymal hematoma risk acutely. The score needs external validation and could be useful for patient stratification in stroke trials. Key words: acute ischemic stroke, computed tomography, CT angiography, outcome, thrombus Introduction From current intravenous (i.v.) thrombolysis trials in acute ischemic stroke, only i.v. thrombolysis with tissue plasmino- gen activator (tPA) within 3 h from symptom onset compared with placebo demonstrated an effect on improved functional outcome (1). Vascular imaging was not a prerequisite in any of these trials. However, spontaneous or treatment induced recanalization until 24 h from symptom onset was associated with improved functional outcomes in recent studies (2–4). Patients with intracranial occlusion may therefore represent a Correspondence: Volker Puetz à , Postdoctoral Fellow. Calgary Stroke Program, Department of Clinical Neuroscience, Foothills Hospital, 1403 29th street NW, Calgary, Alberta, Canada. Tel: 11 403 944 2618; Fax: 11 403 944 1602; e-mail: volker.puetz@calgaryhealthregion.ca 1 University of Calgary, Department of Clinical Neurosciences, Calgary Stroke Program, Canada 2 University of Technology Dresden, Dresden Stroke Center, Germany 3 University of Calgary, Departments of Community Health Sciences and Medicine, Canada 4 Ananthapuri Hospitals and Research Institute, Thiruvananthapuram, India 5 Seaman Family MR Research Centre, Foothills Medical Centre, Calgary Health Region, Canada 6 National Neurosciences Center, Kolkata, India & 2008 The Authors. 230 Journal compilation & 2008 World Stroke Organization International Journal of Stroke Vol 3, November 2008, 230–236