Emphysematous Pyelonephritis (EPN) Workup

Updated: Mar 12, 2021
  • Author: Sugandh Shetty, MD, FRCS; Chief Editor: Edward David Kim, MD, FACS  more...
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Approach Considerations

A high index of suspicion is important when attempting to diagnose emphysematous pyelonephritis (EPN) promptly. Recommended laboratory studies and expected results include the following:

  • Urinalysis - Pyuria, infected urine
  • Complete blood cell count with differential - Leukocytosis with a left shift, thrombocytopenia
  • Renal function tests - Elevated creatinine level
  • Blood cultures - Positive

Patients with urosepsis and shock should undergo cardiac and pulmonary function assessment as needed.

Imaging study findings that can raise suspicion of EPN include an abnormal gas shadow in the renal bed on plain radiography (kidney, ureters, bladder [KUB] view), and the presence of intrarenal gas on renal ultrasonography. [7] Computed tomography (CT) scanning is the definitive imaging test for EPN. [22, 23, 7]


Imaging Studies

Imaging studies used for diagnosis of emphysematous pyelonephritis include the following:

  • Kidney, ureter, bladder (KUB) radiographs
  • Renal ultrasonography
  • Computed tomography (CT) - The definitive technique

Patients should be stabilized with intravenous fluids and intravenous antibiotics prior to radiologic intervention. For full discussion, see Imaging in Emphysematous Pyelonephritis

Kidneys, ureter, and bladder imaging

KUB films often reveal gas distribution over the region of the kidneys, as shown in the images below. In patients with emphysematous pyelitis, the collecting system may be filled with gas. An ileus pattern may be seen, suggesting retroperitoneal inflammation.

Kidneys, ureter, and bladder imaging showing a str Kidneys, ureter, and bladder imaging showing a streaky gas pattern over the entire right kidney in a patient with emphysematous pyelonephritis.
Emphysematous pyelonephritis. Kidneys, ureter, and Emphysematous pyelonephritis. Kidneys, ureter, and bladder imaging showing gas over the region of the right kidney. White arrows outline the area. The faint outline of a staghorn calculus can be seen in the right kidney.


Renal ultrasonograms often reveal high echogenic areas with dirty shadowing. Hydronephrosis and perinephric fluid may also be seen. (See the image below.

Computed tomography

Patterns seen on CT in patients with EPN (see the images below) may include the following:

  • Streaky, streaky and mottled, or streaky and bubbly
  • Gas may be rimlike or crescent-shaped in the perinephric area
  • Gas may be seen in the renal vein or inferior vena cava (see the images below)
  • Gas may be seen along the psoas muscle
  • Perinephric abscess may lead to significant gas accumulation in the perinephric space
  • A stone may be seen in the collecting system


CT scan showing right renal and perinephric gas in CT scan showing right renal and perinephric gas in a patient with emphysematous pyelonephritis.
CT scan showing gas in both kidneys and the inferi CT scan showing gas in both kidneys and the inferior vena cava in a patient with bilateral emphysematous pyelonephritis.

Radiologic Classification

Over time, several groups of investigators have proposed classification systems for EPN; these are outlined below. Note that the classifications are not comparable.

In 1970, Langston and Pfister described 3 main radiographic patterns in EPN, as follows [24] :

  • Diffuse mottling of the renal parenchyma
  • Bubbly renal parenchyma surrounded by crescent-shaped gas in the perinephric space
  • Extension of gas through the Gerota fascia

In 1984, Michaeli et al suggested 3 stages of EPN, as follows [25] :

  • Stage I - Gas within the renal parenchyma or the perinephric tissue
  • Stage II - Presence of gas in the kidney and its surroundings
  • Stage III - Extension of gas through Gerota fascia or bilateral EPN

In 1996, Wan et al described 2 distinct types of EPN, as follows [26] :

  • Type I - Characterized by parenchymal destruction, with streaky or mottled parenchymal gas and an absence of fluid collection; has a fulminant course and high risk of mortality
  • Type II - Characterized by renal or perirenal fluid collection, with bubbly gas collection in the perinephric space or in the collecting system and a mortality rate of 18%; according to Wan et al, the compromised immune state of the host leads to fulminant and dry-type EPN, which is fatal

In 2000, Huang and Tseng modified the staging proposed by Michaeli et al, as follows [4] :

  • Class 1 - Gas confined to the collecting system
  • Class 2 - Gas confined to the renal parenchyma alone
  • Class 3A - Perinephric extension of gas or abscess
  • Class 3B - Extension of gas beyond the Gerota fascia
  • Class 4 - Bilateral EPN or EPN in a solitary kidney