Xanthogranulomatous pyelonephritis presenting with a left flank mass.

We present a case of a patient with xanthogranulomatous pyelonephritis (XGP) presenting with a large (18 × 12 cm) left-sided flank mass with worsening left flank pain. CT abdomen/pelvis demonstrated a left kidney with parenchyma replaced by multiple large hypodense collections containing fluid and gas, a left staghorn calculus, and a communication between the kidney and large flank collection. About 4.5 weeks after initial presentation, the patient underwent operative intervention. Pathology revealed an end-stage kidney with scar consistent with xanthogranulomatous pyelonephritis.