Renal vs Perinephric Abscess

Today we discussed the case of a young man presenting with RLQ/flank pain and hematuria, found on imaging to have a renal abscess vs mass! We had an interesting discussion on renal vs perinephric abscesses.


  • Both renal and perinephric abscesses can be caused by contiguous spread (most commonly from urologic infections) versus hematogenous spread (less common, but suspect in immunocompromised patients or those with risk factors such as IVDU)
  • Indications for drainage differ for renal vs perinephric abscesses, based on size criteria (see below)



Renal vs Perinephric Abscess

  • Renal abscess is a walled-off cavity, whereas perinephric abscess is diffuse liquefaction between renal capsule and Gerota’s fascia
  • Both renal and perinephric abscesses can result from local spread (from Gram negative urologic infection) or from hematogenous seeding (ie. Staph aureus)
  • Clinical manifestations of both abscesses are similar – fever, vague abdominal pain, fatigue, sweats, constitutional symptoms. Symptoms of UTI (dysuria, frequency) are not common manifestations of both types of abscesses.
  • Choice of antibiotic therapy is generally targeted towards gram negative coverage (unless concern for hematogenous spread of staphylococcus is high).
  • Generally, renal abscesses occur more frequently than perinephric abscess.
  • Renal abscess
    • Majority of cases are complications of urologic infection from renal stone or vesicoureteral reflux
    • Less commonly, acute pyelonephrosis can develop into tissue necrosis by forming a walled-off cavity.
    • Rare cause is “renal carbuncle” secondary to staph bacteremia & hematogenous spread.
  • Perinephric abscess
    • Local spread of infection can be outward diffusion of a renal infection or from a non-renal contiguous source (from the liver, gallbladder, pancreas, Crohn’s, appendicitis, vertebral osteomyelitis)
    • Can also occur from hematogenous seeding, mostly staphylococcal
  • What other entities can masquerade as renal/perinephric abscesses?
    • Papillary necrosis: we discussed sickle cell patients & patients on chronic analgesics!
    • Emphysematous pyelonephritis – gas producing necrotizing infection
    • Malakoplakia: rare granulomatous inflammatory disease associated with E. coli infection. CT shows enlarged kidney with multiple hypovascular masses.
    • Xanthogranulomatous pyelonephritis: unusual variant of chronic pyelonephritis where there is massive destruction of the kidney due to granulomatous tissue containing, lipid-laden macrophages
    • Renal Cell Carcinoma: may be hard to distinguish radiographically from a renal abscess
  • When to drain? Based on the size!
    • For renal abscesses: Drain if size is > 5 cm
    • For perinephric abscesses: > 3 cm

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