Urothelial cancer of the renal pelvicaliceal system: unusual imaging manifestations.

Unusual imaging features of urothelial cancer of the renal pelvicaliceal system can be challenging for any radiologist. These manifestations include noncalcified and calcified focal infiltrative parenchymal masses, incidentally detected tumors in a hydronephrotic kidney due to ureteropelvic junction obstruction, transpelvic infiltrating solid masses extending through the retroperitoneum, and tumors primarily invading the perirenal fat. Less common manifestations include massive papillary frond-like projections within a large hydronephrotic sac, large multiloculated cystic masses with thick and irregular septa, tumors invading the renal vein, and paraaortic lymph node metastases as the only sign of an undetectable primary tumor of the renal collecting system. Radiologists should be aware that an eccentric, focal, infiltrative pelvicaliceal carcinoma that causes distortion of the renal contour may simulate renal cell carcinoma; when calcified, such a pelvicaliceal carcinoma may simulate chronic inflammatory renal disease. The radiologist should also be aware of the importance of a meticulous sonographic evaluation of a hydronephrotic kidney, particularly in older patients, to avoid missing a urothelial cancer. When a nonfunctioning and enlarged kidney is present, radiologists should always consider infiltrative hydronephrotic urothelial carcinoma as a diagnostic possibility. Familiarity with unusual imaging features of urothelial cancer of the renal pelvicaliceal system may facilitate making the correct diagnosis, thus enabling adequate therapeutic management.