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Case 365 - Discussion

Uploaded: 2009-10-21, Updated: 2009-10-21


Xanthogranulomatous Pyelonephritis



  • A distinctive form of subacute and chronic renal inflammation prone to form a mass lesion that may mimic a renal neoplasm.

  • Mostly female in the fourth to sixth decades of life.

  • Most common presentations, fever, flank pain, and a tender flank mass.

  • Nephrolithiasis in up to 70% of patients.

  • Affected kidney is nonfunctioning in 50 - 70% of patients.

  • Common urinary tract bacteria, Proteus and Escherichia, can be isolated from the lesion itself in 95% of cases.

  • Almost always unilateral, but may involve any part or all of the kidney.


  • In the early stage, confined to the kidney, golden yellow nodules,  a few millimeters to several centimeters.

  • By the time of clinical detection, the lesion is usually very large and may have penetrated Gerota's fascia, mimicking RCC both clinically and pathologically.


  • Variable features.

  • Purulent foci with microabscesses and numerous neutrophils;

  • Classic histopathology of abundant, lipid-laden macrophages intermixed with lymphocytes and plasma cells. The lipid-laden macrophages (xanthoma cells) may mimic the cells of well-differentiated clear cell RCC.

  • Multinucleated giant cells and spindled fibroblasts may be abundant,  resembling the spindle cell component of a sarcomatoid RCC.

  • These inflammatory elements may have a zonal distribution, with the necrosis and acute inflammation adjacent to the collecting system, surrounded by macrophages with fibrosis and chronic inflammation at the periphery.


  • Clear cell RCC: especially when the xanthoma cells are abundant.

  • Sarcomatoid RCC

  • MalakoplakiaIn:  presence of Michaelis-Gutmann bodies.


  • AFIP, tumor of the kidney, bladder and related urinary structures, series 4