Xanthogranulomatous pyelonephritis characterized on PET/CT

A 35-year-old black woman was referred for a PET/CT scan to evaluate the malignant potential of retroperitoneal lymphadenopathy seen on a CT scan done at an outside institution. The patient had a history of a left-sided renal staghorn calculus and had a stent placed in the left collecting system after extracorporeal shockwave lithotripsy. She remained febrile despite an extensive course of antibiotics. The PET/CT demonstrated a left kidney with CT findings characteristic for xanthogranulomatous pyelonephritis with abnormal F-18 FDG uptake on PET. The retroperitoneal adenopathy had only mild FDG uptake characteristic for benign inflammation.