Angiomyolipoma and renal cell carcinoma: US differentiation.

PURPOSE: To analyze whether shadowing and other ultrasound (US) features were helpful for distinguishing angiomyolipoma (AML) from renal cell carcinoma (RCC). MATERIALS AND METHODS: US images were reviewed of 49 patients with RCC and 35 patients with AML. Each tumor was evaluated for size, location, echogenicity, homogeneity, shadowing, hypoechoic rim, and intratumoral cysts. When available, computed tomographic (CT) scans of AMLs were analyzed for the amount of fat and soft tissue in each lesion. RESULTS: AMLs tended to be smaller and more frequently echogenic than RCCs, but statistically significant overlap occurred. Shadowing was seen in 12 (33%) AMLs but was not seen in RCCs. Hypoechoic rims and intratumoral cysts were seen only in RCCs (numbers were too small to perform further statistical analysis). CONCLUSION: In hyperechoic renal masses, the presence of shadowing, a hypoechoic rim, and intratumoral cysts are important findings that may help distinguish AML from RCC.