eMedicine Specialties > Radiology > Genitourinary
Emphysematous Pyelonephritis
Updated: Jan 25, 2008
Introduction
Background
Emphysematous pyelonephritis (EPN) is a life-threatening, fulminant, necrotizing upper urinary tract infection associated with gas within the kidney and/or perinephric space. Some confusion exists regarding the terminology; the term emphysematous pyelonephritis should be reserved for renal tract infections with intraparenchymal renal gas. Gas confined to the renal pelvis should be called emphysematous pyelitis, and gas confined to the perinephric space should be called perinephric emphysema.1,2,3,4,5,6
EPN is usually a rapidly progressive and life-threatening infection that is seen most commonly in persons with diabetes.7 The infecting organisms usually consist of mixed flora, including Escherichia coli (68%), Klebsiella pneumoniae (9%), and Proteus mirabilis. Other organisms include Pseudomonas; Enterobacter; Candida; and, rarely, Clostridia. Females are affected twice as often as males, and mortality rates can be as high as 80%. Obstructive uropathy, urinary calculi, calyceal stenosis, and neoplasms are significant predisposing factors.
EPN in a solitary, polycystic, transplanted kidney has been described, with a rare association with xanthogranulomatous pyelonephritis. Often, multiple conditions are associated with EPN, such as poorly controlled diabetes, acidosis, dehydration, and electrolyte imbalance.
Patients usually present with chills, fever, flank pain, lethargy, and confusion. Septicemic shock may occur. A crepitant mass may be present. Often, bacteriuria, positive blood culture results, and leukocytosis are present. Patients are usually quite ill, but occasionally, the symptoms are mild, belying the severity of the disease. This is particularly the case in persons with long-standing diabetes. The condition is bilateral in 5-7% patients.8
Treatment involves aggressive antibiotic therapy, drainage procedures to relieve obstruction, and prompt nephrectomy in life-threatening situations.
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Diabetes Mellitus, Type 2
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Pathophysiology
EPN is an acute and chronic necrotizing pyelonephritis with multiple renal abscesses. Mixed acid fermentation of glucose by Enterobacteriaceae bacteria is the major pathway of gas formation.
Two subtypes of EPN based on CT appearances have been described. Type I EPN (33% of patients) is characterized by parenchymal destruction with either absence of fluid collection or presence of streaky or mottled gas radiating from the medulla to the cortex. A crescent of subcapsular or perinephric gas may be present. The absence of fluid collection implies a poor immune response. The mortality rate is high, at 66%. Type II EPN (66% of patients) typically has a confined, bubbly, intrarenal gas pattern — probably within abscesses associated with renal and perinephric fluid collection — and gas within the renal pelvis. The mortality rate in type II is 18%.9
Conversion from type I EPN to type II EPN has been described.10 Wan et al have shown that serum creatinine levels are the most reliable predictors of the outcome in patients with EPN. By calculating likelihood ratios, patients with creatinine levels greater than 1.4 mg/dL and platelet counts of 60,000/mm3 or less are at high risk.11 The posttest probability of death increases from 69% to 92% in type I EPN and 18% to 53% in type II EPN. Patients with creatinine levels of 1.4 mg/dL or less and platelet counts greater than 60,000/mm3 are at much lower risk. The posttest mortality risk in these patients decreases from 69% to 27% and from 18% to 4% for type I EPN and type II EPN, respectively.11
Frequency
United States
EPN is rare, but the frequency is higher in patients who are immunocompromised, especially in patients with diabetes, who account for 87-97% of patients.9
Mortality/Morbidity
The mortality rate is 60-75% with antibiotic therapy and 21-29% after antibiotic treatment and nephrectomy. When the infection extends into the perinephric space, the mortality rate increases sharply, to 80%.
Race
No racial predilection has been noted, but because most cases of EPN are associated with diabetes, the incidence is expected to be higher in races with increased prevalence of diabetes mellitus.
Sex
The male-to-female ratio is 1:2.
Age
The average age of patients with EPN is 54 years.
Presentation
Patients with EPN often have diabetes (87-97%). Females are affected twice as often as men. The mortality rate can be as high as 80%.9 Multiple conditions are associated with EPN, such as poorly controlled diabetes, acidosis, dehydration, and electrolyte imbalance. Treatment involves aggressive antibiotic therapy, drainage procedures to relieve obstruction, and prompt nephrectomy in life-threatening situations.8
- Patients usually present with chills, fever, flank pain, lethargy, and confusion not responding to treatment.
- EPN may cause fever of unknown origin in 18% of patients.
- Septicemic shock and abdominal symptoms are less common manifestations.
- A crepitant mass may be present.
- Bacteriuria, positive blood culture results, and leukocytosis are often present.
- A presentation with pneumaturia has been described.
- Patients are usually quite ill, but occasionally, the symptoms are mild, belying the severity of the disease. This is particularly the case in patients with long-standing diabetes.
- EPN is bilateral in 5-7% patients.
- The role of imaging is paramount in the management of such cases, if an early diagnosis is to be made and a potentially devastating outcome is to be avoided.
Preferred Examination
Plain abdominal radiography is the initial examination of choice because it better depicts air in the renal collecting system and it is much more specific than ultrasonography. However, in practice, sonography may be the initial examination performed.11,12,13,14,15
Computed tomographic (CT) findings are diagnostic of the presence of air within the renal tract, and CT also elegantly depicts the renal and perirenal anatomy and the spread of infection to the perinephric tissues.13,16
Because function is depressed or even absent on the affected side, radionuclide studies are more appropriate for assessing renal function, particularly if surgery is indicated.
Intravenous urography may be necessary if renal intervention is contemplated.
Limitations of Techniques
Plain radiographs are good for depicting air within the renal collecting system, but nonspecificity is a problem because of the superimposition of gas from the bowel. Moreover, gas in the retroperitoneum and gas within a renal or perinephric abscess may mimic EPN.
Similarly, sonography is limited because gas within the kidney and/or renal pelvis mimics renal calculi and produces artifact due to reverberation echoes and shadowing.
CT scans do not always depict other causes of intrarenal air, such as reflux of air from the bladder and bronchorenal, enterorenal, or cutaneorenal fistulae. These may occur with xanthogranulomatous pyelonephritis and focal renal abscesses.17
The sole limitation of radionuclide imaging is its lack of availability. Otherwise, it is an excellent modality, and it does not result in false-positive or false-negative diagnoses.
Differential Diagnoses
Emphysema
Other Problems to Be Considered
Retroperitoneal perforation of an abdominal viscus
Psoas abscess secondary to gas-forming organisms
Reflux of air from the bladder
Bronchorenal, enterorenal, or cutaneorenal fistulae (as may occur with xanthogranulomatous pyelonephritis)
Air in a focal renal abscess (not life threatening)
Gas in the renal parenchyma may be seen in conditions other than emphysematous pyelonephritis on CT. Intraparenchymal renal gas may be seen following urologic intervention such as that for a nephrostomy insertion or a fistulous communication between the gastrointestinal tract and the renal collecting system. These situations do not represent clinical emergencies and are not life-threatening, as in emphysematous pyelonephritis. With the increasing use of abdominal CT, radiologists, especially in the emergency setting, should be aware of this comparatively rare finding and should be familiar with its differential diagnosis.
EPN has been described as a presenting feature of a urinary bladder adenocarcinoma in a middle-aged nondiabetic patient.18
Radiography
Findings
- Plain radiographs may show bubbles of gas within the region of the renal bed and in the upper renal collecting system. These may be diagnostic in the appropriate clinical setting.14
- Gas within the collecting system without evidence of renal parenchymal gas may be seen in patients with diabetes and does not have the same ominous prognosis.
- Intravenous urography shows significant renal enlargement associated with delayed or absent excretion.
- Acute renal edema with obliteration of the renal pelvis can be seen.
- Retrograde pyelography can be used to establish the presence of ureteral obstruction.
Degree of Confidence
Plain radiographic findings may be diagnostic in ill patients with diabetes who have signs of acute pyelonephritis.
False Positives/Negatives
Renal fossa gas may be confused with gastrointestinal gas. A false-positive diagnosis may occur with retroperitoneal gas and a psoas abscess secondary to gas-forming organisms. Reflux of air from the bladder and bronchorenal, enterorenal, or cutaneorenal fistulae (as may occur with xanthogranulomatous pyelonephritis17 ) may also lead to false-positive findings. Air can be seen in focal renal abscesses.
Computed Tomography
Findings
CT is the examination of choice for diagnosing EPN.13,16,19
- Intraparenchymal, intracalyceal, and intrapelvic gas and extension into the perinephric space are readily identified on nonenhanced CT scans.19
- Mottled areas of low attenuation extend radially along the pyramids.
- Occasionally, pus may be seen extending into the renal veins.
Degree of Confidence
CT is the most reliable and sensitive modality in diagnosing EPN.
False Positives/Negatives
EPN should be differentiated from reflux of air from the bladder and bronchorenal, enterorenal, or cutaneorenal fistulae (as may occur with xanthogranulomatous pyelonephritis17 ). Air also can be seen in focal renal abscesses, but it is not life threatening.
Magnetic Resonance Imaging
Findings
MRI is not the modality of choice in the diagnosis of EPN. MRI findings reported are a signal void on both T1-weighted and T2-weighted images. Perinephric and intraparenchymal fluid collections are demonstrated well on MRIs.13,14
Degree of Confidence
MRI is not the modality of choice in the diagnosis of EPN. When CT is available, it should be used instead.
False Positives/Negatives
Signal voids on MRIs may occur with renal calculi or rapidly flowing blood.
Ultrasonography
Findings
- Intrarenal gas causes high-amplitude echoes within the renal sinus/renal parenchyma associated with dirty acoustic shadowing.
- Ring-down artifacts may result from air bubbles trapped in fluid.
- Shadowing from gas bubbles in the perinephric space may be seen. These make visualization of the kidney difficult.
- Perinephric fluid, if any, tends to be obscured by gas.
Degree of Confidence
Ultrasonography is usually the first imaging modality for assessing renal pathology. The sonographic findings often guide clinicians in choosing the next modality, such as CT, to achieve a more specific diagnosis.13
False Positives/Negatives
Gas within the kidney and/or renal pelvis mimics renal calculi. In select patients, particularly those with diabetes in whom sonograms suggest renal calculi, obtaining a coned radiograph of the renal area is worthwhile to preclude missing an EPN.
Nuclear Imaging
Findings
Radionuclide studies are nonspecific; therefore, they have a limited role in the evaluation of EPN. However, radionuclide study is an excellent modality for assessing differential function when nephrectomy is contemplated. Scintigraphy has been used to evaluate responses to antimicrobial therapy.
Intervention
Treatment involves aggressive antibiotic therapy, drainage procedures to relieve obstruction, and prompt nephrectomy in life-threatening situations.13,20,21,22
With early diagnosis and the aggressive and prompt administration of antibiotics, therapeutic success may be achieved in select patients.20 Percutaneous nephrostomy and percutaneous perinephric drainage may preclude nephrectomy in some patients. Occasionally, drainage procedures alone are successful; however, most patients require immediate surgical intervention.
Combined treatment of EPN with broad-spectrum antibiotics and percutaneous renal drainage was found to be safe and effective in the treatment of 10 patients with EPN. This treatment may be used an alternative to nephrectomy in high-risk patients not suitable for general anesthesia.20
Medicolegal Pitfalls
- EPN is a rare but life-threatening suppurative infection of the renal parenchyma and perirenal tissues.
- For successful treatment of patients with EPN, appropriate medical therapy should be initiated, and immediate nephrectomy or drainage should not be delayed.
- Although percutaneous drainage combined with antibiotics is an acceptable alternative, surgery should not be delayed. As to the stage at which surgery should be performed, the decision should be based on a combination of imaging and clinical findings.
- Serum creatinine levels are the most reliable predictors of the outcome.
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Multimedia
Media file 1: In a 58-year-old woman with diabetes, emergency intravenous pyelography (IVP) had been requested for an evaluation of flank pain. After this scout image was obtained, a lateral radiograph (see Image 2) was obtained, and the IVP was canceled and CT (see Images 3-4) was performed. This anteroposterior (AP) scout image shows striated intrarenal gas (within medullary rays) and perinephric gas.
Media file 2: The lateral image confirms that the gas is present within the kidney, overlying the spine (same patient as in Images 1, 3, and 4).
Media file 3: CT scan depicts the intrarenal gas very well. The contralateral kidney looks normal (same patient as in Images 1, 2, and 4).
Media file 4: Magnified CT obtained with a lung window setting better reveals the striated intrarenal gas and subcapsular gas in the posterior aspect (same patient as in Images 1-3).
Media file 5: Sonogram of the right kidney in a 52-year-old woman demonstrates echogenic gas within the collecting system and posterior cortex of the right kidney. The involvement of the posterior cortex is partly obscured by shadowing from the gas in the collecting system.
Media file 6: CT scan through the top of the right kidney in a 52-year-old woman (same patient as in Images 5, 7, and 8) with emphysematous pyelonephritis. Gas is present in the upper pole cortex of the kidney. Note normal excretion of contrast material in the left kidney.
Media file 7: CT scan through the middle of the right kidney in a 52-year-old woman (same patient as in Images 5, 6, and 8) with emphysematous pyelonephritis. Gas is present in the cortex and collecting system of the kidney, with some extension into the perinephric space.
Media file 8: CT scan through the lower portion of the right kidney in a 52-year-old woman (same patient as in Images 5-7) with emphysematous pyelonephritis. Gas is present in the collecting system and anterior cortex of the kidney.
Media file 9: Axial contrast-enhanced CT scans showing gas within the renal collecting system and the urinary bladder following bladder urologic intervention (Images 9-11)
Media file 10: Axial contrast-enhanced CT scans showing gas within the renal collecting system and the urinary bladder following bladder urologic intervention (Images 9-11)
Media file 11: Axial contrast-enhanced CT scans showing gas within the renal collecting system and the urinary bladder following bladder urologic intervention (Images 9-11)
References
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Jain SK, Agarwal N, Chaturvedi SK. Emphysematous pyelonephritis: a rare presentation. J Postgrad Med. Jan-Mar 2000;46(1):31-2. [Medline].
Roy C, Pfleger DD, Tuchmann CM, et al. Emphysematous pyelitis: findings in five patients. Radiology. Mar 2001;218(3):647-50. [Medline].
Sathyanathan VP, Gomathy S, Potty RN, et al. Emphysematous pyelonephritis. J Assoc Physicians India. Jun 1998;46(6):562-3. [Medline].
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Falagas ME, Alexiou VG, Giannopoulou KP, Siempos II. Risk factors for mortality in patients with emphysematous pyelonephritis: a meta-analysis. J Urol. Sep 2007;178(3 Pt 1):880-5; quiz 1129. [Medline].
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Grozel F, Berthezene Y, Guerin C, et al. Bilateral emphysematous pyelonephritis resolving to medical therapy: demonstration by US and CT. Eur Radiol. 1997;7(6):844-6. [Medline].
Huang JJ, Tseng CC. Emphysematous pyelonephritis: clinicoradiological classification, management, prognosis, and pathogenesis. Arch Intern Med. Mar 27 2000;160(6):797-805. [Medline].
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Punekar SV, Kinne JS, Rao SR, et al. Xanthogranulomatous pyelonephritis presenting as emphysematous pyelonephritis: a rare association. J Postgrad Med. Oct-Dec 1999;45(4):125. [Medline].
Singh I, Pachisia SS, Kumar S, Arora VK, Kumar P. Emphysematous pyelonephritis: a consequence of adenocarcinoma of urinary bladder in a nondiabetic patient. J Postgrad Med. Oct-Dec 2005;51(4):324-5. [Medline].
Portnoy O, Apter S, Koukoui O, Konen E, Amitai MM, Sella T. Gas in the kidney: CT findings. Emerg Radiol. Jun 2007;14(2):83-7. [Medline].
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Keywords
EPN, upper urinary tract infection, renal tract infections with intraparenchymal renal gas, emphysematous pyelitis, perinephric emphysema, urinary tract infection, gas in the kidney, renal gas, Escherichia coli, E coli, Klebsiella pneumoniae, K pneumoniae, Proteus mirabilis, P mirabilis
Contributor Information and Disclosures
Author
Ali Nawaz Khan, MBBS, FRCS, FRCP, FRCR, LRCP, Chairman of Medical Imaging, Professor of Radiology, NGHA, King Fahad National Guard Hospital, King Abdulaziz Medical City, Riyadh, Saudi Arabia
Ali Nawaz Khan, MBBS, FRCS, FRCP, FRCR, LRCP is a member of the following medical societies: American Institute of Ultrasound in Medicine, Radiological Society of North America, Royal College of Physicians, Royal College of Physicians and Surgeons of the United States, Royal College of Radiologists, and Royal College of Surgeons of England
Disclosure: Nothing to disclose.
Coauthor(s)
Sumaira MacDonald, MBChB, PhD, MRCP, FRCR, Lecturer, Sheffield University Medical School; Endovascular Fellow, Sheffield Vascular Institute
Sumaira MacDonald, MBChB, PhD, MRCP, FRCR is a member of the following medical societies: British Medical Association, Royal College of Physicians, and Royal College of Radiologists
Disclosure: Nothing to disclose.
Colm Boylan, MRCP, FRCR, Specialist Registrar, Department of Radiology, North Manchester General Hospital NHS Trust, UK
Colm Boylan, MRCP, FRCR is a member of the following medical societies: Royal College of Radiologists
Disclosure: Nothing to disclose.
Brendan Costello, MD, Clinical Director, Department of Urology, North Manchester General Hospital
Brendan Costello, MD is a member of the following medical societies: British Medical Association
Disclosure: Nothing to disclose.
Khalid Mahmood, MBBS, FCPS, Locum Appointment Training Specialist Registrar, Department of Radiology - Paediatric, Royal Liverpool (Alder Hey) Children's Hospital
Disclosure: Nothing to disclose.
Medical Editor
Steven Perlmutter, MD, FACR, Clinical Associate Professor, Radiology Residency Program Director, Radiology Medical Director, Department of Radiology, University Hospital at Stony Brook
Steven Perlmutter, MD, FACR is a member of the following medical societies: American College of Radiology, American Institute of Ultrasound in Medicine, American Medical Association, American Roentgen Ray Society, Association of Program Directors in Radiology, Association of University Radiologists, Medical Society of the State of New York, Radiological Society of North America, Society of Breast Imaging, Society of Nuclear Medicine, and Society of Uroradiology
Disclosure: Nothing to disclose.
Pharmacy Editor
Bernard D Coombs, MB, ChB, PhD, Consulting Staff, Department of Specialist Rehabilitation Services, Hutt Valley District Health Board, New Zealand
Disclosure: Nothing to disclose.
Managing Editor
Arnold C Friedman, MD, FACR, Associate Chairman, Department of Radiology, University of Florida Health Science Center; Chief, Department of Radiology, Shands-Jacksonville Hospital
Arnold C Friedman, MD, FACR is a member of the following medical societies: American College of Radiology, American Institute of Ultrasound in Medicine, American Roentgen Ray Society, Association of University Radiologists, and Radiological Society of North America
Disclosure: Nothing to disclose.
CME Editor
Robert M Krasny, MD, Consulting Staff, Department of Radiology, The Angeles Clinic and Research Institute
Robert M Krasny, MD is a member of the following medical societies: American Roentgen Ray Society and Radiological Society of North America
Disclosure: Nothing to disclose.
Chief Editor
Eugene C Lin, MD, Consulting Staff, Department of Radiology, Virginia Mason Medical Center
Eugene C Lin, MD is a member of the following medical societies: American College of Nuclear Medicine, American College of Radiology, Radiological Society of North America, and Society of Nuclear Medicine
Disclosure: Nothing to disclose.