Standardized assessment of leptomeningeal collaterals: a comparative review.

Leptomeningeal collaterals (LMCs) strongly influence outcomes in acute ischemic stroke (AIS), but their small caliber makes visualization challenging with computed tomography angiography (CTA) and magnetic resonance angiography (MRA). Digital subtraction angiography (DSA) remains the gold standard for anatomical and functional LMC assessment but is invasive and typically reserved for patients undergoing mechanical thrombectomy. Several grading systems have been proposed to noninvasively assess LMCs on acute-phase CTA and MRA. However, no consensus exists on which system best captures the complex anatomy of LMCs, and considerable variability in interrater reliability, standardization, and clinical feasibility. Here, we review collateral grading systems based on single-phase CTA, the most widely used acute stroke imaging modality, and compare them with DSA-based collateral scoring. We summarize the relevant literature on the clinical importance of LMCs and their impact on treatment outcomes in AIS. Because automated, reproducible collateral scoring could provide clinicians with more objective ratings of LMCs but has not yet entered clinical routine, we also discuss the potential benefits and implications of incorporating automated collateral scoring into routine brain imaging and clinical practice.