Intracranial thrombus extent predicts clinical outcome, final infarct size and hemorrhagic transformation in ischemic stroke: the clot burden score


Volker Puetz*, Postdoctoral Fellow. Calgary Stroke Program, Department of Clinical Neuroscience, Foothills Hospital, 1403 29th street NW, Calgary, Alberta, Canada. Tel: +1 403 944 2618; Fax: +1 403 944 1602; e-mail:


Background In ischemic stroke, functional outcomes vary depending on site of intracranial occlusion. We tested the prognostic value of a semiquantitative computed tomography 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 infraclinoid internal carotid artery. We retrospectively studied patients with disabling neurological deficits (National Institute of Health Stroke Scale score ≥5) and computed tomography angiography within 24-hours from symptom onset. We analyzed percentages independent functional outcome (modified Rankin Scale score ≤2), final infarct Alberta Stroke Program Early Computed Tomography Score and parenchymal 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 score<10 was associated with reduced odds of independent functional outcome (odds ratio 0·09 for clot burden score≤5; odds ratio 0·22 for clot burden score 6–7; odds ratio 0·48 for clot burden score 8–9; all versus clot burden score 10; P<0·02 for all). Lower clot burden scores were associated with lower follow-up Alberta Stroke Program Early CT Scores (P<0·001) and higher parenchymal hematoma rates (P=0·008). Inter-rater reliability for clot burden score was 0·87 (lower 95% confidence interval 0·71) and intra-rater reliability 0·96 (lower 95% confidence interval 0·92).

Conclusion The quantification of intracranial thrombus extent with the clot burden score predicts functional outcome, final infarct size and parenchymal hematoma risk acutely. The score needs external validation and could be useful for patient stratification in stroke trials.