eMedicine Specialties > Radiology > Genitourinary

Emphysematous Pyelonephritis

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
Coauthor(s): Sumaira MacDonald, MBChB, PhD, MRCP, FRCR, Lecturer, Sheffield University Medical School; Endovascular Fellow, Sheffield Vascular Institute; Colm Boylan, MRCP, FRCR, Specialist Registrar, Department of Radiology, North Manchester General Hospital NHS Trust, UK; Brendan Costello, MD, Clinical Director, Department of Urology, North Manchester General Hospital; Khalid Mahmood, MBBS, FCPS, Locum Appointment Training Specialist Registrar, Department of Radiology - Paediatric, Royal Liverpool (Alder Hey) Children's Hospital
Contributor Information and Disclosures

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.

Related eMedicine topics:
Diabetes Mellitus, Type 1
Diabetes Mellitus, Type 2
Polycystic Kidney Disease

Related Medscape topics:
Resource Center Diabetes: Incretin Hormones in Diabetes and Metabolism
Resource Center Diabetic Microvascular Complications
Resource Center Sepsis
Resource Center Kidney & Pancreas Transplant

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

• Search for CME/CE on This Topic »

• Emphysematous Pyelonephritis (Urology)
• Renal Corticomedullary Abscess (Urology)
• Pyelonephritis, Acute (Nephrology)