Emphysematous pyelonephritis

Emphysematous pyelonephritis refers to a  morbid infection of kidneys, with characteristic gas formation within or around the kidneys. If not treated early, it may lead to fulminant sepsis and carries a high mortality.

The patient usually presents with flank pain, urinary tract obstruction with fever. Leukocytosis and hyperglycemia (in diabetics) are prominent laboratory findings. Thrombocytopenia is particularly associated with poor prognosis 3.


It tends to be more common in females. Approximately 90% of patients have uncontrolled diabetes 1. It may however also be seen in immunocompromised individuals or associated with urolithiasis, neoplasms or sloughing of papilla.

Causative organisms include

  • E. Coli: usually considered the commonest causative organism 3
  • Klebsiella pneumonia
  • Proteus mirabilis
Plain film and fluoroscopy (IVP)

May show mottled gas within renal fossa or crescentic gas collection within Gerota's fascia. Linear gas shadows along paraspinal region may also be seen, representing retroperitoneal air.

  • may show an enlarged kidney with coarse echoes within renal parenchyma or collecting system.
  • dirty echogenic foci with reverberation/ring-down artifacts representing air ('dirty shadowing') may also be seen

Bowel gas over kidneys may lead to false positive diagnosis.


CT is the best diagnostic modality for emphysematous pyelonephritis. It may show following diagnostic features

  • enlarged, destructed renal parenchyma
  • small bubbly or linear streaks of gas 1
  • fluid collections, with gas-fluid levels
  • focal necrotic areas +/- abscess

CT features of emphysematous pyelonephritis differentiates into two types:

  • type 1
    • greater than one-third renal parenchymal destruction
    • streaky or mottled appearance of gas
    • intra- or extrarenal fluid collections are characteristically absent
    • it is usually more aggressive and lead to death shortly, if not intervened early
    • mortality 70%
  • type 2
    • destruction of less than one-third of the parenchyma
    • renal or extrarenal collections associated with bubbly or loculated gas, or gas within pelvicalyceal system or ureter
    • mortality 20%

In addition to this, the Huang-Tseng CT classification system 4 is also described:

  • class 1: gas in collecting system only
  • class 2: gas in renal parenchyma only (without extrarenal extension)
  • class 3: gas in renal parenchyma with extrarenal extension
    • class 3a: extension of gas or abscess to perinephric space
    • class 3b: extension of gas or abscess to pararenal space
  • class 4: bilateral emphysematous pyelonephritis or solitary kidney with emphysematous pyelonephritis

In mild cases, intravenous antibiotics are administered and percutaneous catheter drainage of perirenal or retroperitoneal collections is done. Severe cases often warrant a nephrectomy.

General imaging differential considerations include

  • emphysematous pyelitis
  • iatrogenic (instrumentation, or intervention of urinary tract)
  • ureter-ileosigmoidostomy or fistulous communication with bowel
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Article information

rID: 16234
System: Urogenital
Section: Pathology
Synonyms or Alternate Spellings:
  • EPN
  • Emphysematous pyelonephritis (EPN)

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Cases and figures

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