Renal replacement lipomatosis with coexisting xanthogranulomatous pyelonephritis in a pregnant woman.

Renal replacement lipomatosis of the kidney is a rare entity characterized by renal sinus and perirenal fat proliferation often caused by renal calculi. Most of the renal parenchyma is replaced by fat and the kidney is usually small, atrophic and nonfunctioning. We report magnetic resonance imaging and ultrasonography findings of a pregnant woman with xanthogranulomatous pyelonephritis and renal replacement lipomatosis coexisting in the same kidney.