Figure 12a. Squamous cell carcinoma in a 50-year-old man with chronic calculus disease and left flank pain. (a) Axial unenhanced CT scan shows a high-attenuation stone (arrow) in the left renal pelvis. A tiny amount of air (arrowhead) due to previously performed percutaneous nephrostomy is seen in the renal sinus. (b) Axial contrast-enhanced CT scan obtained during the excretory phase shows an infiltrative mass (arrows) in the renal pelvis that extends to the renal parenchyma. Note the metastatic lymph nodes (arrowhead) in the paraaortic space.