American Urological Association - Xanthogranulomatous Pyelonephritis

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Home Education AUAUniversity Education Products & Resources Pathology for Urologists Kidney Inflammatory/Necrotic Renal Lesions Xanthogranulomatous Pyelonephritis

Xanthogranulomatous Pyelonephritis

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  • Destructive chronic histiocytic inflammation (xanthoma cells) of pelvicaliceal and renal parenchyma forming a mass or pseudotumorous lesion.
  • Often associated with gram-negative bacteria.
  • Occurrence associated with obstruction, stones or staghorn calculus and recurrent urinary tract infections.
  • Begins with obstruction, followed by suppurative inflammation at pelvis then extends into kidney medulla, resulting to a "destructive" appearing inflammation and necrosis.
  • More common in females (70%).
  • Presents with renal mass, pain and fever; renal mass raises concern for a neoplasm.
  • Gross:
    • Multiple irregular yellow masses usually associated with inflamed and necrotic pelvis and medulla (image A).
    • May have renal calculus.

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  • Histology:
    • Inflammatory infiltrates of mostly foamy histiocytes admixed with acute and chronic inflammatory infiltrates (images B).
    • Central clusters of neutrophils surrounded by xanthoma cells and peripheral fibrosis (image C).
    • Later stage will have fibrosis (image D).
  • Rare malakoplakia of the kidney considered as part of the spectrum; malakoplakia is characterized by histiocytes (von Hansemann histiocytes) containing intracytoplasmic concretions called Michaelis-Gutmann bodies.
  • Kidney is usually not functional; nephrectomy is performed because of the symptoms and to exclude malignancy for the mass lesion.

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