Sonographic differentiating criteria for small angiomyolipomas (<= 3 cm) and renal cell carcinomas.

Purpose: The purpose of this prospective study was to analyze whether ultra sound (US) features are helpful for the differentiation and characterizatio n of small solid (less than or equal to 3 cm) renal masses. Materials and M ethods: 70 small solid (less than or equal to 3 cm) renal masses were evalu ated sonographically with respect to size, location, echogenicity, homogene ity, shadowing, hypoechoic rim, and cystic regions. In addition, all masses were evaluated with spiral-computed tomography (CT). A diagnosis of angiom yolipoma (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 o n CT was correlated with the presence of shadowing seen on sonography. Resu lts: 10 (29 %) of the 35 renal cell carcinomas (RCC) were hyperechoic to re nal parenchyma, but no RCC was as echogenic as the renal sinus fat. Acousti c shadowing was only observed in AML. 11 (34 %) AML with shadowing tended t o 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 car cinomas display a broad range of echogenicities indicating that small RCC ( less than or equal to 3 cm) and AML are not definitely distinguishable by t heir type of echogenicity. The presence of shadowing, a hypoechoic rim, and cystic regions enable differentiation of small (less than or equal to 3 cm ) AML from RCC with a high specificity. Accordingly, sonography has the pot ential to characterize small (less than or equal to 3 cm) hyperechoic renal masses, with high specificity. However, the low sensitivity of these US fe atures may require a CT for accurate diagnosis.