Massive Renal Replacement Lipomatosis With Foci of Xanthogranulomatous Pyelonephritis in a Horseshoe Kidney

Renal replacement lipomatosis (RRL) is a rare condition that occurs at the end of the spectrum of renal tissue replacement by fat. Xanthogranulomatous pyelonephritis (XGP) is a granulomatous inflammation characterized by destruction of renal parenchyma and replacement by lipid-laden macrophages. We present the case of a 75-year-old man who complained of severe anemia 34 years after right nephrolithotomy. Computed tomography revealed a huge low-density mass with renal parenchyma atrophy on the right side of horseshoe kidney. Right nephrectomy was performed. Pathological diagnosis was RRL with XGP. This is the first report of RRL with XGP in a horseshoe kidney.