Clear Cell Likelihood Score (ccLS) v2.0 — Renal Mass mpMRI

The ccLS is a standardized Likert scale derived from multiparametric MRI that estimates the probability of clear cell renal cell carcinoma in an indeterminate solid renal mass; version 2.0 is the current algorithm. Eligibility requires absence of unequivocal macroscopic fat (which instead indicates classic angiomyolipoma) and enhancement in at least 25% of the mass (predominantly non-enhancing lesions are cystic and belong to the Bosniak pathway). Three major criteria are assessed in every eligible mass: T2 signal intensity relative to renal cortex (hypo-, iso- or hyperintense), corticomedullary-phase enhancement relative to cortex (intense >75%, moderate 40-75%, mild <40%), and presence of microscopic fat on chemical-shift imaging. Intensely enhancing masses with microscopic fat score 5; intensely enhancing hyper- or isointense masses without microscopic fat score 3-4 (segmental enhancement inversion tips to 3); moderately enhancing masses score 2-3 (segmental enhancement inversion tips to 2); mildly enhancing hyperintense masses score 3, isointense masses score 1-2 (marked diffusion restriction tips to 1) and hypointense masses score 1. T2-hypointense intensely enhancing masses branch on the arterial-to-delayed enhancement ratio (ADER): ADER of 1.5 or more suggests fat-poor AML (ccLS 2-3), while ADER below 1.5 suggests ccRCC (ccLS 3-4), with homogeneity and marked diffusion restriction resolving each range. In branches where microscopic fat is not otherwise used, unequivocal microscopic fat upgrades the score to at least 3. Tier meanings: 1 very unlikely, 2 unlikely, 3 intermediate, 4 likely, 5 very likely. In a multi-center evaluation the pooled proportion of ccRCC was 6% for ccLS 1, 38% for ccLS 2 (small sample), 32% for ccLS 3, 72% for ccLS 4 and 81% for ccLS 5; a ccLS of 4 or higher carried 84% malignancy.