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Xanthogranulomatous Pyelonephritis

Definition: Chronic infection of kidney and surrounding tissues characterized by destruction and replacement of renal parenchyma by lipid-laden macrophages.

Findings:

• Best diagnostic clue: Obstructing calculus with atrophic or nonfunctioning kidney and perirenal fibrofatty proliferation.
• Contracted pelvis; dilated calices
• Centrally obstructing calculus; staghorn (75%)

DDx: RCC, TCC, mets/lymphoma, abscess

XGP features:

• Location
  • Unilateral (most cases) > bilateral
  • 2 forms of XGP
    • Diffuse (83-90%): Involves entire kidney
    • Segmental or focal (10-17%): Tumefactive due to obstructed single infundibulum; one moiety of duplex system
• Size: 2.5-5.8 cm; mean is 3.8 cm
• Morphology: Well-circumscribed mass with global or focal renal enlargement
• Other general features
  • 3 stages of XGP
    • Stage 1: Lesion confined to kidney
    • Stage 2: Lesion extends to perirenal space
    • Stage 3: Lesion spreads to pararenal spaces ± abdominal wall
      
• Complications: Hepatic dysfunction (reversible), extrarenal extension, fistulas (e.g., pyelocutaneous, ureterocutaneous), hemorrhage
• Treatment
  • Antibiotics: Treatment prior to surgical intervention
  • Nephrectomy usually required
    • Radical nephrectomy in complete XGP
    • Partial nephrectomy in focal XGP
      

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