Xanthogranulomatous pyelonephritis

Xanthogranulomatous pyelonephritis

  • Middle-aged to elderly patients (female), diabetes has been described as a risk factor
  • Related to staghorn calculi
  • A chronic granulomatous process inciting a chronic but incomplete immune reaction –> granulation tissues & lipid laden macophages replace normal renal tissues around the stone
  • Generalized inflammation in the affected kidney often spreads into adjacent structures, including fistulaization and psoas abscess formation.

Imaging features

  • Presence of staghorn calculi
  • An enlarged hypoattenuating kidney (inflammation) with a contracted pelvis, dilated calyces seen as bear paw sign


  •  Surgical nephrectomy is usually curative. The degree of inflammatory involvement of adjacent structures may favor an open approach in many cases.

Reference: radiopaedia.org


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