Xanthogranulomatous Pyelonephritis

Key points

• Xanthogranulomatous pyelonephritis (XGP) is a chronic destructive inflammatory renal disease associated with long-standing infection and obstruction, often producing a poorly functioning kidney.
• Proteus mirabilis is a classic association, although other organisms can be involved; renal calculi, especially staghorn calculi, are common.
• Foamy lipid-laden macrophages are characteristic histological findings.
• Typical presentation includes flank pain, fever, recurrent UTI and sometimes a palpable renal mass or constitutional symptoms.
• Imaging can mimic renal malignancy. CT is particularly useful and may strongly suggest XGP; nephrectomy is often required for extensive unilateral non-functioning disease but diagnosis is not necessarily made only after nephrectomy.
• MRCP discriminator: staghorn calculus + chronic UTI + enlarged poorly functioning kidney + inflammatory mass → XGP.
• Imaging trap: XGP can resemble renal cell carcinoma; CT is central to assessment.