Xanthogranulomatous pyelonephritis presenting as giant gluteal abscess.

Xanthogranulomatous pyelonephritis (XGP) is a rare chronic suppurative granulomatous infection of the kidney associated with renal obstruction and progressive renal parenchymal destruction. We present an unusual clinically occult case of extensive right XGP which presented clinically with discharging right gluteal sinus and swollen right posterolateral chest and abdominal walls extending caudally to right gluteus. Contrast enhanced computed tomography of the abdomen and pelvis revealed obstructing right renal calculi, severe hydronephrosis, renal destruction and large (20.7 × 10.2 × 14.7 cm) abscess extending caudally to right gluteus. Histopathology of the specimen was concluded as right xanthogranulomatous pyelonephritis. This case demonstrates how distant an insidious XGP can infiltrate. It also emphasizes the need to have a broad range of differential diagnoses including XGP when presented with a case of gluteal abscess and sinus. Contrast enhanced computed tomography plays a key role in evaluating the cause, extent and complications of XGP and is also useful in pretreatment planning.