Renal cell carcinoma containing fat: demonstration with CT.

It is widely believed that demonstration of fat within a well-marginated renal tumor at computed tomography (CT) is highly suggestive of angiomyolipoma and can rule out renal cell carcinoma. The authors describe a patient in whom CT demonstrated a solid mass containing calcifications and small amounts of fat. Renal cell carcinoma was diagnosed at pathologic examination. The carcinoma had tubular and papillary architectural configurations associated with areas of osseous metaplasia located in the fibrous stroma of the tumor. Renal cell carcinoma should be considered in the differential diagnosis of well-marginated lipomatous renal tumors when intratumoral calcifications are identified at CT. Such calcified, fat-containing renal tumors must be evaluated with surgical exploration and treated as any other indeterminate renal tumors.