Renal replacement lipomatosis. Review and case report

Renal Replacement Lipomatosis Presenting in the Setting of Ureteral Stricture with Absence of Renal Calculus Disease

Renal replacement lipomatosis of the kidney is a rare, benign entity in which extensive fibrofatty proliferation of the renal sinus is associated with marked atrophy of the renal parenchyma. It is often associated with calculi or long-standing inflammation. This entity may be confused with a fatty neoplasm of the kidney. A 51-year-old woman with a past medical history of pancreas transplant for type 1 diabetes subsequently developed ureteral stricture. This was initially managed by a nephrostomy tube and nephroureterostomy stenting with periodic exchanges to help restore urine flow; however, the renal function of the kidney progressively declined with recurrent and complicated urinary tract infections. She presented for kidney transplant with right native nephrectomy. Gross examination of the right kidney revealed a 12.8 cm renal sinus lipomatous mass replacing much of the kidney. Microscopically, the mass consisted of mature adipose tissue with fibrous septae and occasional thick-walled vessels with prominent smooth muscle bundles. A rare atypical stromal cell was present, otherwise no significant cytologic atypia or lipoblasts were identified. After excluding fat-predominant angiomyolipoma and well-differentiated liposarcoma, a diagnosis of renal replacement lipomatosis was made. Renal replacement lipomatosis is a benign condition typically associated with a nonfunctioning or poorly functioning kidney often linked to renal calculus disease or chronic renal infection. The presentation in our case was atypical given an absence of associated renal calculus disease. This case is intended to increase awareness of this less commonly encountered entity as it may be confused with a fatty neoplasm of the kidney, some with malignant potential.

Excessive proliferation of peripelvic fat of the kidney

Excessive proliferation of the peripelvic fat of the kidney (EPPF) is a benign process with an innocuous effect on the patient. However, this condition may assume major clinical significance by producing pyelocalyceal deformities that may be mistaken for true renal masses. Rarely, EPPF may masquerade as a renal pelvic tumor. We present the second reported case of EPPF simulating a renal pelvic tumor and review the history as well as the characteristic radiographic and sonographic features of this condition.