Background: Clot size in acute ischemic stroke has been ascribed to time from onset, used in imaging selection with varying techniques or definitions, and cited as a factor in both revascularization success and clinical outcomes. We analyzed clot size on noncontrast CT, CT angiography (CTA) and digital subtraction angiography (DSA) in the multicenter TREVO and TREVO 2 trials.
Methods: Imaging core labs of the TREVO and TREVO 2 trials conducted pooled analyses of the CT/CTA and DSA datasets. Clot size was independently measured by hyperdense middle cerebral artery sign (HMCAS) length on noncontrast CT thin-slice reconstruction, CTA length, clot burden score (CBS) and DSA prior to thrombectomy. Statistical analyses included descriptive statistics and correlation analyses among clot size measures, and time from onset to CT or onset to DSA. Logistic regression analysis was used to model 90-day good outcome and revascularization success.
Results: 116 TREVO and TREVO 2 subjects from the pooled imaging dataset were analyzed with respect to clot size. Clot size estimated from thin-slice reconstruction of HMCAS was mean 7.6±9.2 mm, however, 41% of cases with proven arterial occlusion did not have HMCAS. CTA length of clots was mean 12.3±7.3 mm, with corresponding HMCAS CTA length in 41%. CBS (range 0-10) was mean 6.7±1.8. DSA clot length was mean 10.6±5.7 mm. Moderate correlations were noted between clot size on CT, CTA and DSA. Time from onset to CT or onset to DSA was unrelated to any clot size, yet worse ASPECTS scores were linked with larger clots (HMCAS length, ρ=-0.290, p=0.004; CTA length, ρ=-0.302, p=0.009). Revascularization success (TICI≥2B) was lower with CTA clot length > 8 mm (OR 0.32 [0.11, 0.99], p=0.047) when distal opacification via collaterals was present, yet unrelated to any HMCAS clot length. Good clinical outcome (mRS 0-2 at 90 days) was unrelated to any measure of clot size.
Conclusions: Clot size varies depending on imaging technique and definitions, with a substantial proportion of occlusions that cannot be measured on either noncontrast CT or CTA and “time is clot” requires further study. Larger clots are associated with worse ASPECTS, possibly negating potential clinical benefit of successful revascularization.