[Criteria for ultrasound differentiation of small angiomyolipomas (< or = 3 cm) and renal cell carcinomas]

Abstract

Purpose: The purpose of this prospective study was to analyze whether ultrasound (US) features are helpful for the differentiation and characterization of small solid (< or = 3 cm) renal masses.

Materials and methods: 70 small solid (< or = 3 cm) renal masses were evaluated sonographically with respect to size, location, echogenicity, homogeneity, shadowing, hypoechoic rim, and cystic regions. In addition, all masses were evaluated with spiral-computed tomography (CT). A diagnosis of angiomyolipoma (AML) was made when a lesion contained components with attenuation of fat (> -10 HU). The amount of fat and soft tissue of an AML detected on CT was correlated with the presence of shadowing seen on sonography.

Results: 10 (29%) of the 35 renal cell carcinomas (RCC) were hyperechoic to renal parenchyma, but no RCC was as echogenic as the renal sinus fat. Acoustic shadowing was only observed in AML. 11 (34%) AML with shadowing tended to have a larger amount of soft tissue. A hypoechoic rim and cystic regions were only found in RCC. 14 of 35 (40%) RCC showed a hypoechoic rim. Cystic regions were found in 12 of the 35 RCC (34%).

Conclusions: Renal cell carcinomas display a broad range of echogenicities indicating that small RCC (< or = 3 cm) and AML are not definitely distinguishable by their type of echogenicity. The presence of shadowing, a hypoechoic rim, and cystic regions enable differentiation of small (< or = 3 cm) AML from RCC with a high specificity. Accordingly, sonography has the potential to characterize small (< or = 3 cm) hyperechoic renal masses, with high specificity. However, the low sensitivity of these US features may require a CT for accurate diagnosis.