Idiopathic renal replacement lipomatosis: a rare renal pseudo tumor.

Renal replacement lipomatosis (RRL) is a rare condition that occurs as an end result of renal atrophy or destruction of renal parenchyma by excessive lipomatous tissue in renal sinus and perinephric space. We report a case of RRL presenting as a right renal mass clinically. Intra-venous pyelography and renal scan revealed a left non-functioning kidney. A left nephrectomy was performed. After histopathological examination and extensive literature search, a diagnosis of RRL was given. In majority of cases, it is associated with renal calculi. Idiopathic variety is not common. It is a rare entity and the diagnosis may be missed due to lack of experience. It has to be differentiated from other fat-containing tumors such as renal lipoma, xanthogranulomatous pyelonephritis, angiomyolipoma and liposarcoma.