This is a case of pathologically proven xanthogranulomatous pyelonephritis (and a staghorn calculus). This case demonstrates the classic "bear paw appearance" of xanthogranulomatous pyelonephritis.

The pathologic examination from the right radical nephrectomy grossly demonstrated cysts with tan-green purulent material. Further dissection revealed diffusely scatted, multiloculated cysts that contained yellow to tan-gray pus-like material. Multiple stones were seen within the calyces and pelvis. Histopathologically, the renal parenchyma contained foamy histocytes, occasional giant cells, "thyroidization" of the kidney, and marked acute and chronic inflammatory changes. The enlarged pericaval lymph node was dissected, which only revealed a reactive lymph node without evidence for malignancy.

Co-authors:
Michael Schuster, MD
Christine Cooley, MD