Angiomyolipoma with minimal fat: differentiation of morphological and enhancement features from renal cell carcinoma at CT imaging

Background Angiomyolipoma (AML) with minimal fat may mimic renal cell carcinoma (RCC) and is difficult to distinguish from RCC with imaging studies alone. Precise diagnostic strategies have been explored to discern AML with minimal fat from RCC. Purpose To compare the morphological and enhancement features of AML with minimal fat with those of size-matched RCC on computed tomography (CT). Material and Methods Our study included 143 pathologically proved renal tumors (29 AML with minimal fat: mean diameter, 2.5cm; range, 1.2-4cm; 114 RCC: mean diameter, 2.8cm; range, 1.3-4cm). All patients underwent biphasic helical CTs. Two radiologists retrospectively evaluated the morphological (i.e. non-round and round appearances, with or without capsule) and enhancement features (i.e., wash-out, gradual, or prolonged). For the parameters that had statistically significance between the two groups, we calculated the positive and negative predictive values by using the univariate (2) test. P<0.05 indicated a significant difference. Results AML with minimal fat showed a non-round appearance without a capsule (n=24, 83%) and prolonged enhancement (n=20, 69%). The positive and negative predictive values of the non-round appearance without capsule for differentiating AML with minimal fat from RCC were 82.8% and 95.6%, respectively. The positive and negative predictive values of prolonged enhancement were 62.5% and 90.8%, respectively. These features were valuable predictors for AML with minimal fat from RCC. Conclusion CT images with non-round shape without capsule and prolonged enhancements may be used to differentiate AML with minimal fat from RCC.