CT of unusual renal masses invading the pelvicaliceal system: potential mimics of upper tract transitional cell carcinoma

Two patients with renal cell carcinoma and one patient with metastasis to the kidney from colorectal cancer are reported because all three cases manifested at computed tomography (CT) as a renal mass invading the pelvicaliceal system and radiologically simulating transitional cell carcinoma. Recognition that the CT finding of a renal mass with invasion of the pelvicaliceal system is not always indicative of a transitional cell carcinoma broadens the differential diagnosis in this setting and might potentially alter the diagnostic and therapeutic approach.