[Characterization of renal masses]

The characterization of renal masses relies mainly on CT which remains the gold standard in the diagnosis of renal tumors and cysts. Ultrasound enables to diagnose benign cysts which account for the majority of incidentally detected renal masses. MR imaging is useful in the diagnosis of renal masses that remain indeterminate at CT. Moreover, it is efficient as a substitute when CT is contraindicated. Renal masses include three categories with respect to the size and the gross architecture of the lesion: indeterminate very small masses (less than 10mm in diameter); cystic renal masses and solid renal masses that exhibit postcontrast tumor tissue enhancement. Characterization of cystic renal masses relies mainly on the Bosniak classification which consists of four categories: benign simple cysts (cat I); minimally complicated cysts (cat II); indeterminate cystic renal masses that include cystic renal tumors (multiloculated or not) and complex cysts; cystic renal cell carcinomas (cat IV). Solid renal masses include pseudotumors (normal variants, renal dysmorphisms and inflammatory renal masses) and renal neoplasms among which CT enable to distinct: typical large renal cell carcinomas, typical fat-containing angiomyolipomas and indeterminate renal tumors.