Stage III xanthogranulomatous pyelonephritis with sarcomatoid degeneration.

Xanthogranulomatous pyelonephritis (XGP) is an uncommon chronic condition characterized by destructive granulomatous disease of the kidney with uncertain etiology. Significant risk factors for XGP are represented by the coexistence of history of nephrolithiasis, diabetes mellitus, recurrent urinary tract infections and other immunocompromised conditions. It is also associated with higher risk of malignancy, reported in up to 11% of patients. We report a case of a 76-year-old female who presented to the emergency department with an insidious onset of abdominal and right lower back pain. She had a history of renal stones and diabetes mellitus. On physical examination, a painful fistulous orifice in skin on the right lumbar region was found. CT images showed a nonfunctioning right kidney replaced by multiple necrotic cavities with inflammatory involvement of the right hepatic lobe and a nephron-cutaneous fistula. These CT findings were strongly suggestive of XGP (III state). CT images obtained before and after the administration of intravenous contrast material showed also a hyper-vascularized renal mass with irregularly thickened walls confirmed by a targeted CEUS examination and suspicious for malignancy. Pathologic examination confirmed the chronic pyelonephritis and revealed evidence of a concomitant sarcomatoid lesion. This case underlines the central role of a multimodality imaging approach in the emergency department and how this affects the correct management and treatment of patients. In fact, MDCT is considered the current gold standard for the diagnosis and the staging of XPG but the contrast-enhanced ultrasound (CEUS) in selected patients can increase the diagnostic accuracy in the uncertain small renal masses detected on CT scans.