• ring signA 60-year-old woman presents to the emergency room with fever, chills, sudden flank pain, and gross hematuria. She has a history of recurrent urinary tract infections. Urinalysis reveals pyuria, hematuria, proteinuria, and dead tissue. An intravenous urography is obtained, revealing a ring sign. She is immediately given hydration and appropriate antibiotics.
  • Clinical definition
    • necrosis and sloughing of renal papillae
  • Epidemiology
    • incidence
      • 30-40% in those with sickle cell disease or trait
    • demographics
      • middle-aged adults
      • uncommon in children, except in those with sickle cell disease or trait
    • risk factors
      • sickle cell disease or trait
      • acute severe pyelonephritis
      • analgesics such as NSAIDs
        • one of the most common and preventable risk factors
        • phenacetin
      • diabetes mellitus
      • tubulointerstitial nephritis
      • kidney stones causing obstruction
      • indinavir (anti-retroviral drug)
      • congenital urinary tract obstructions such as posterior urethral valves
      • shock
  • Pathogenesis
    • in sickle cell disease or trait
      • increased blood viscocity in the renal medulla causes renal papillary infarcts
        • the renal medulla has a low oxygen tension resulting in red blood cell sickling
    • in analgesic use
      • NSAIDs inhibits prostaglandin synthesis
        • prostaglandins promote vasodilation
  • Prognosis
    • prognostic variable
      • negative
        • concomitant diabetes
        • older age
  • History
    • may be chronic and asymptomatic or acute
    • gross blood in urine
    • may have history of recent infection or autoimmune flare
    • pyelonephritis
  • Symptoms
    • primary symptoms
      • fever and chills
      • sudden onset flank or abdominal pain
    • may be asymptomatic
  • Physical exam
    • tenderness to palpation in the flank or abdomen
  • This clinical image of angiogram shows the string-of-beads appearance of fibromuscular dysplasia.Radiographs
    • indications
      • if obstruction such as kidney stones is suspected
      • not diagnostic
    • recommend views
      • kidneys, ureters, and bladder (KUB)
    • findings
      • hydronephrosis from obstruction
      • may visualize kidney stones
  • CT
    • indications
      • typically performed if patient presents with hematuria, even if renal papillary necrosis is suspected, as hematuria can indicate malignancy in the bladder
      • if renal obstruction is suspected
      • most accurate test
    • views
      • CT of abdomen and pelvis
    • findings
      • hydronephrosis
      • kidney stones
      • ring shadows in medullae
      • loss of papillae
  • Intravenous urography
    • indications
      • if CT scan is inconclusive and suspicious for renal papillary necrosis remains high
      • if there is no suspicion of obstruction but suspicion of renal papillary necrosis remains high
    • findings
      • shrinkage of renal papillae
      • ring shadow from desquamated papillae - “ring sign”
      • filling defect in renal pelvis
      • contrast-containing tiny cavities in papillae
  • Labs
    • serum creatinine
      • if there is a sudden rise in creatinine, consider renal papillary necrosis in patient with diabetes or chronic urinary obstruction
  • Urinalysis
    • best initial test and results may show
      • hematuria
      • pyuria
      • proteinuria
      • sloughed papillae
  • Nephrolithiasis         
    • kidney stone seen on imaging without evidence of renal papillary necrosis
  • Tubulointerstitial nephritis
    • often presents with rash, arthralgias, and eosinophilia in the urine


  • Conservative
    • avoid analgesics or any other nephrotoxic medications
  • Medical
    • supportive care with fluid resuscitation
      • indications
        • for all patients
    • antibiotics
      • indications
        • if pyelonephritis is suspected
  • Chronic pyelonephritis
  • Sepsis

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