From the archives of the AFIP - Transitional cell carcinoma of the urinary tract: Radiologic-pathologic correlation

The urothelium is a target tissue for carcinogens that lead to the development of transitional cell carcinomas (TCCs), both synchronous and metachronous. Although there are pathologic and imaging features common to transitional cell tumors occurring anywhere in the genitourinary tract, certain findings are more typical of tumors of the renal pelvis, ureter, or urinary bladder. A slightly irregular, fixed mass arising from any urothelial surface is characteristic of TCC. Although such masses are usually confined to the collecting system lumina, larger lesions that arise in the renal pelvis may extend into the renal parenchyma, typically in an infiltrative pattern that preserves the reniform shape. In contrast to the rapidly developing mural edema associated with obstructing calculi, the relatively slow growth of ureteral TCC allows for gradual expansion of the ureteral lumen around the tumor and is less likely to produce acute renal colic. Focal wall thickening, either eccentric or circumferential, may also be a manifestation of TCC of the ureter or, less commonly, other portions of the urinary tract. The urinary bladder is the most common site of TCC; lesions are generally confined to the lumen and typically do nor extend beyond the bladder wall until quite large.