Imaging description

A reported 61% (22 of 36) to 77% (24 of 31) of small renal cell carcinomas are hyperechoic relative to the adjacent renal parenchyma at ultrasound, and 32% (10 of 31) are uniformly and markedly echogenic such that they mimic angiomyolipomas (Figures 45.1 and 45.2) [1, 2]. Larger renal cell carcinomas are usually hypoechoic. Given that there is no particularly plausible reason for echogenicity to depend on tumor size, it is possible that this relationship is artifactual due to diagnostic bias. That is, smaller hypoechoic renal cell carcinomas are less likely to cause contour deformities or other mass effects and may be missed, while small echogenic renal cell carcinomas stand out relative to the renal parenchyma and are more likely to be detected [3].

Importance

The primary concern is that a renal cell cancer misdiagnosed as an angiomyolipoma might progress and become incurable. Based on the available evidence and given that the frequency with which small echogenic renal masses represent renal cell carcinoma rather than angiomyolipoma is unknown, it has been suggested that all non-calcified echogenic renal lesions found on ultrasound need further evaluation with CT [4]. This may be a counsel of perfection, since in practice supplementary CT is inconsistently recommended and often ignored [5]. I have been unable to find any reports of a fatal renal cell carcinoma that was initially diagnosed as an angiomyolipoma on ultrasound. This may mean the majority of small echogenic masses are truly angiomyolipomas, or might just as well reflect the fact that small incidental renal cell carcinomas are often indolent and arguably subclinical [6].