Early-stage clear cell tubulopapillary renal cell carcinoma: imaging features and distinction from clear cell and papillary subtypes

Abstract

Purpose: Clear cell tubulopapillary renal cell carcinoma (CCTPRCC) is a recently described, low grade subtype of renal cancer. We determined if imaging features could be used to distinguish early-stage CCTPRCC from stage-matched clear cell RCC (ccRCC) and papillary RCC (pRCC). Subjects and Methods: This IRB-approved retrospective study included 54 stage-Ia patients with pathologically-confirmed CCTPRCC (n=18), ccRCC (n=18), and pRCC (n=18). CT (n=48) and MRI (n=27) exams were reviewed and imaging features compared. Continuous variables were evaluated using ANOVA and Tukey's multiple comparison tests. Categorical variables were compared using Chi square test or Fisher's exact test. Results: Compared to pRCC, CCTPRCC had a lower mean attenuation value on unenhanced CT (p<0.017), was more often hyperintense on T2-weighted images (p<0.0001), showed an ill-defined margin (p=0.003), and demonstrated nonenhancing areas (p=0.0003). The presence of all three of these statistically significant features (hypoattenuation [unenhanced attenuation < 25HU], ill-defined margin, nonenhancing areas) yielded an area under the Receiver Operator Curve (ROC) of 0.92 (95% CI: 0.83-0.99) for differentiating CCTPRCC from pRCC. There were no significant differences in the imaging features of CCTPRCC and ccRCC. Conclusions: Early stage clear cell tubulopapillary renal cell carcinoma can be distinguished from papillary RCC based on low attenuation on unenhanced CT, high intensity on T2-weighted images, an ill-defined margin, and presence of nonenhancing areas, but cannot be distinguished from clear cell RCC.