Figure 4b. Replacement lipomatosis of the renal sinus and periureteral space in a 63-year-old man with chronic renal calculus disease. A percutaneous nephrostomy tube was inserted for stone extraction. CT was performed because procedure-related hemorrhage was suspected. (a) Axial contrast-enhanced CT scan shows a tumorlike mass of fat (arrows) that occupies the left renal sinus and surrounds the left ureter (u). The left renal parenchyma is markedly atrophied in association with a large stone (arrowhead), and a large amount of subcapsular hematoma (H) is also seen. Note the percutaneous nephrostomy tube. (b) Photograph of the surgical specimen shows the markedly atrophied kidney (arrows) containing several stones; the kidney is surrounded by fatty tissue (F).