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  • Mounica Chidurala and Kevin Rice, MD

Emphysematous Pyelonephritis

Updated: Mar 23, 2022

90 yo F with UTI. Diagnosis? • Xray of the Week

CT Scan of Emphysematous Pyelonephritis

Figure 1. Non-contrast CT abdomen & pelvis of a 90-year-old female.

CT Scan of Emphysematous Pyelonephritis Annotated

Figure 2. Figure 1: Non-contrast CT abdomen & pelvis of a 90-year-old female with a UTI demonstrating emphysematous pyelonephritis and a renal stone within the renal pelvis.

A. Coronal non-contrast CT of abdomen & pelvis showing gas (green arrow) and renal stone (red) within the renal pelvis.

B. Axial non-contrast CT of abdomen & pelvis showing gas (green arrow) and renal stone (red arrow) within the renal pelvis.

C. Axial non-contrast CT of abdomen & pelvis showing gas within the bladder (orange arrow).


Emphysematous pyelonephritis (EPN) is a necrotizing infection that leads to gas formation within the renal parenchyma, collecting system, and/or perinephric areas. It is commonly seen in patients with uncontrolled diabetes, urinary tract obstruction or urinary stones, or immunocompromised state. Female patients have an increased risk of developing EPN due to higher incidence of UTIs caused by Escherichia coli, Klebsiella pneumonia, and Proteus mirabilis [1]. Like pyelonephritis, patients with EPN often present with fever, abdominal or flank pain, and costovertebral angle tenderness. Urinalysis may show pyuria, leukocytosis, nitrites, hematuria, WBC casts; however, imaging is required to confirm the diagnosis [2,3,4]. CT abdomen and pelvis is the gold standard for confirming EPN [5]. The most comprehensive classification system used to categorize EPN is developed by Huang and Tseng (Table 1) and best correlates with management [4].

Classification of Emphysematous Pyelonephritis

  • Class 1: Gas accumulation in the renal pelvis

  • Class 2: Gas accumulation in the renal parenchyma

  • Class 3A: Gas extension into the perinephric space

  • Class 3B: Gas extension into the pararenal space

  • Class 4: Gas in solitary or bilateral kidneys

Table 1: Classification of Emphysematous Pyelonephritis. [4]

It is likely that the 90-year-old female patient shown in Figure 1 had a complication of EPN due to a UTI and a renal stone causing an obstruction at the renal pelvis. The urinary organisms thrive in an immunocompromised host and lead to a rapid progression from a UTI to EPN [4]. Bacteria within the urinary tract can ferment glucose and albumin and produce H2 and CO2 gas seen in Figure 1 (green and orange arrows) [6]. This case is classified as Class 1 EPN because the gas accumulation is restricted to the renal pelvis and complicated by a renal stone. This can be managed with antibiotics, percutaneous catheter drainage (PCD), fluid, electrolyte, and glucose control (Fig. 4) [4].

Emphysematous Pyelonephritis Treatment

Figure 4. The flowchart for management of emphysematous pyelonephritis (EPN) according to the clinicoradiological classification. Asterisk indicates the presence of 2 or more of the following risk factors: thrombocytopenia, acute renal failure, disturbance of consciousness, and shock. KUB indicates kidneys, ureter, and bladder (plain abdominal radiograph); CT, computed tomography; and PCD, percutaneous catheter drainage. From: Emphysematous Pyelonephritis: Clinicoradiological Classification, Management, Prognosis, and Pathogenesis Arch Intern Med. 2000;160(6):797-805. doi:10.1001/archinte.160.6.797 Copyright © 2000 American Medical Association. All rights reserved. Date of download: 7/25/2021

EPN is a life-threatening condition that warrants an immediate treatment. Most common cause of death in EPN is caused by urosepsis and has a mortality rate of 19-75% [7, 8]. In severe cases or patients who do not respond to PCD, treatment with nephrectomy can lead to clinical and radiological improvement (Fig. 4) [4].


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  1. Ubee SS, McGlynn L, Fordham M. Emphysematous pyelonephritis. BJU Int. 2011;107(9):1474-1478. doi:10.1111/j.1464-410X.2010.09660.x

  2. Kuo CY, Lin CY, Chen TC, et al. Clinical features and prognostic factors of emphysematous urinary tract infection. J Microbiol Immunol Infect. 2009;42(5):393-400.

  3. Wan YL, Lee TY, Bullard MJ, Tsai CC. Acute gas-producing bacterial renal infection: correlation between imaging findings and clinical outcome. Radiology. 1996;198(2):433-438. doi:10.1148/radiology.198.2.8596845

  4. Huang JJ, Tseng CC. Emphysematous pyelonephritis: clinicoradiological classification, management, prognosis, and pathogenesis. Arch Intern Med. 2000;160(6):797-805. doi:10.1001/archinte.160.6.797

  5. Craig WD, Wagner BJ, Travis MD. Pyelonephritis: Radiologic-Pathologic Review. RadioGraphics. 2008; 28:255-276.

  6. Dhingra KR. A Case of Complicated Urinary Tract Infection: Klebsiella pneumoniae Emphysematous Cystitis Presenting as Abdominal Pain in the Emergency Department. West J Emerg Med. 2008;9(3):171-173.

  7. Huang JJ, Chen KW, Ruaan MK. Mixed acid fermentation of glucose as a mechanism of emphysematous urinary tract infection. J Urol. 1991;146(1):148-151. doi:10.1016/s0022-5347(17)37736-4

  8. Michaeli J, Mogle P, Perlberg S, Heiman S, Caine M. Emphysematous pyelonephritis. J Urol. 1984;131(2):203-208. doi:10.1016/s0022-5347(17)50309-2

Mounica Chidurala

Mounica Chidurala is a medical student at Marian University College of Osteopathic Medicine in Indianapolis, IN. Prior to medical school, she graduated from Oklahoma State University with a Bachelor of Science degree in Chemical Engineering, minor in Chemistry, and an Honors College Degree. She also obtained her Master of Science degree in Chemical Engineering from the University of Oklahoma where she defended her master’s thesis in biofuels and heterogeneous catalysis. She is excited to pursue a career in Diagnostic Radiology with interests in Interventional Radiology or Nuclear Medicine. She is passionate about research and innovation in medicine and hopes to teach/mentor students in the future.

Follow Mounica Chidurala on Twitter @mchidurala227

Kevin M. Rice, MD

Kevin M. Rice, MD is the president of Global Radiology CME

Dr. Rice is a radiologist with Renaissance Imaging Medical Associates and is currently the Vice Chief of Staff at Valley Presbyterian Hospital in Los Angeles, California. Dr. Rice has made several media appearances as part of his ongoing commitment to public education. Dr. Rice's passion for state of the art radiology and teaching includes acting as a guest lecturer at UCLA. In 2015, Dr. Rice and Natalie Rice founded Global Radiology CME to provide innovative radiology education at exciting international destinations, with the world's foremost authorities in their field. In 2016, Dr. Rice was nominated and became a semifinalist for a "Minnie" Award for the Most Effective Radiology Educator.

Follow Dr. Rice on Twitter @KevinRiceMD and Linkedin


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