Paediatric xanthogranulomatous pyelonephritis with reno-psoas fistula, psoas abscess and migration of renal calculi.

Xanthogranulomatous pyelonephritis (XGP) is a rare form of chronic pyelonephritis characterized by granulomatous tissue replacing renal parenchyma, primarily in adults. It's often linked to chronic obstruction, urolithiasis, and pyelonephritis, with rare associations with psoas abscess or fistula. A 15-year-old girl, initially treated conservatively for suspected pyelonephritis, underwent CT imaging due to non-response. This revealed XGP with a sizable psoas abscess caused by a kidney-psoas muscle fistula and renal calculus migration. Treatment involved percutaneous abscess drainage, open right nephrectomy, and a prolonged antibiotic regimen.