RADIOLOGY: KIDNEY: Case# 32910: LEFT TCC. This is a 65 year old male with possible transitional cell carcinoma of the left renal pelvis detected on IVP. An enhancing soft tissue mass is seen filling almost all of the left renal pelvis. Minimal amount of contrast is seen around the mass without definite evidence of hydronephrosis. The mass is enhancing with CT number on pre-contrast study approximately 25 and post contrast CT number approximately 65 hounsfield units. There is no other soft tissue mass involving the right kidney, either ureter or urinary bladder. No significant intra-abdominal or pelvic lymphadenopathy is seen. Uroepithelial tumors account for 5 to 10% of renal tumors. 85% of these are transitional cell carcinomas while the remainder are usually squamous cell carcinomas. Hematuria is common, and these tumors usually present earlier than renal cell carcinomas. Most transitional cell tumors have a papillary growth pattern and are attched to the mucosa by a stalk. Non-papillary tumors are flat or nodular and usually agressive. They more commonly cause strictures in the collecting system and ureters. CT typically shows a low attenuating (15-30H) soft tissue mass within the renal pelvis or renal sinus, distorting and compressing the collecting system. Transitional cell carcinoma is readily differentiated from renal calculi on CT images since its numbers are much less than even radiolucent calculi (150-200H). Metastases to liver, lung, and bone occur, and multiple tumors are common. Patients with upper pole tumors have multicentric tumors in 20-44% of cases, and those with TCC of the ureter develop TCC of the bladder in 20-37% of cases.