Renal cell carcinoma: unusual imaging manifestations.

Unusual radiologic manifestations of a renal cell carcinoma (RCC) can present a diagnostic challenge. These manifestations include bilateral synchronous multifocal tumors, a small RCC with synchronous adrenal metastasis, and RCC associated with bulky abdominal lymphoma. Less common manifestations include multiseptated cystic carcinoma simulating a moderately complex renal cyst at ultrasonography (US), paraaortic metastatic adenopathy as the only sign of an undetectable primary renal neoplasm, RCC causing a large arteriovenous fistula, RCC simulating angiomyolipoma, and a nonfunctioning kidney due to transparenchymal renal propagation of cancer associated with a tumor thrombus occluding the renal vein. Radiologists should be aware of the possibility of tumor multifocality or of adrenal metastases from a high-grade small renal tumor, as well as of the association of RCC with lymphoma. They should also be aware of the importance of following up a multiseptated cystic mass found at US or a Bosniak category IIF renal cyst, since these lesions can serve as early indicators of cystic carcinoma. Because the clinical implications of and therapeutic strategies for RCC vary depending on imaging characterization of the nature and extent of the disease, familiarity with its more unusual radiologic manifestations facilitates accurate diagnosis and management.