Case of the Month 2016-06, Page 8

Answer: (D) Bear Paw Sign - The bear paw sign is seen in xanthogranulomatous pyelonephritis and refers to the cross-sectional appearance of the kidney which is said to resemble the paw of a bear. The renal pelvis is contracted whereas the calyces are dilated, mimicking the toe-pads of the paw.

Xanthogranulomatous Pyelonephritis:

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



  • Dull flank pain, fever
  • Palpable mass, weight loss

Lab data

  • Urinalysis: Microscopic hematuria, proteinuria, pyuria
  • Urine culture:
    • Specific bacterial species
    • Negative in up to 25-40 percent of cases
  • ↑ erythrocyte sedimentation rate
  • Abnormal liver function


  • Age
    • Most common: 45-65 years
    • Rare in childhood
    • Focal form more common in children
  • Gender
    • M:F = 1:3-4
  • Epidemiology
    • Incidence: 1 percent of all renal infections

Natural History and Prognosis:

  • Symptomatic six months prior to diagnosis (40 percent of cases)
  • Complications
    • Extrarenal extension
    • Fistulas (pyelocutaneous, ureterocutaneous)
    • Hemorrhage
    • Hepatic dysfunction (reversible)
  • Good prognosis
  • Rare mortality, but morbidity can be substantial


  • Three stages
    • Stage I:  the disease is confined to the renal parenchyma only
    • Stage II: involves renal parenchyma as well as extension to perirenal fat
    • Stage III: the disease extends into the perirenal and para­renal spaces or diffuse retroperitoneum


  • Antibiotic treatment prior to surgical intervention
  • Nephrectomy usually required
    • Radical in diffuse XGP, partial in focal XGP


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