Purpose: The assessment of collateral circulation is an important prognostic factor in patients with stroke due to large vessel occlusion. The results of a recent trial suggested that collateral status could even be used for thrombectomy decision making in patients with late window acute ischemic stroke. However, the reliability of collateral assessment is uncertain. We sought to assess the interrater and intrarater agreement of collateral assessment using multiphase CT angiography.
Methods: Two junior and two senior raters in stroke neurology, diagnostic neuroradiology, and interventional neuroradiology evaluated 60 multiphase CT scans of acute ischemic stroke and scored the presence of collaterals as follows: poor (< 50% collaterals), moderate (≥ 50% but < 100% collaterals), and good (100% collaterals), using the contralateral hemisphere for reference. Agreement was assessed through Fleiss kappa scoring for the global scale and for various dichotomizations.
Results: The overall interrater agreement for the assessment of collaterals on Multiphase CTA was moderate, with higher agreement found among diagnostic neuroradiologists. Dichotomizing the agreement scale into "poor/moderate vs. good" and "poor vs. moderate/good" greatly increased the interrater agreement among all specialties, especially in the latter scenario. Similarly, global intrarater agreement of CTA collateral images was determined to be moderate to substantial, with improvement after dichotomization.
Conclusion: Interrater and intrarater agreement for the global collateral scale was modest, with improvement after dichotomization. Our work suggests that this scale can be reliably used in clinical practice after dichotomization.
Keywords: Acute ischemic stroke; Collateral flow; Large vessel occlusion; Multiphase CTA.
© 2025. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.