You are in: eMedicine Specialties > Radiology > GENITOURINARY Emphysematous PyelonephritisArticle Last Updated: Jan 25, 2008AUTHOR AND EDITOR INFORMATIONSection 1 of 12
  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 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 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 Editors: Steven Perlmutter, MD, FACR, Clinical Associate Professor, Radiology Residency Program Director, Radiology Medical Director, Department of Radiology, University Hospital at Stony Brook; Bernard D Coombs, MB, ChB, PhD, Consulting Staff, Department of Specialist Rehabilitation Services, Hutt Valley District Health Board, New Zealand; Arnold C Friedman, MD, FACR, Associate Chairman, Department of Radiology, University of Florida Health Science Center; Chief, Department of Radiology, Shands-Jacksonville Hospital; Robert M Krasny, MD, Consulting Staff, Department of Radiology, The Angeles Clinic and Research Institute; Eugene C Lin, MD, Consulting Staff, Department of Radiology, Virginia Mason Medical Center Author and Editor Disclosure Synonyms and related 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 INTRODUCTIONSection 2 of 12
  BackgroundEmphysematous 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. PathophysiologyEPN 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 FrequencyUnited StatesEPN 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/MorbidityThe 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%. RaceNo 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. SexThe male-to-female ratio is 1:2. AgeThe average age of patients with EPN is 54 years. Clinical DetailsPatients 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
Preferred ExaminationPlain 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 TechniquesPlain 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. DIFFERENTIALSSection 3 of 12
Emphysema Other Problems to Be ConsideredRetroperitoneal perforation of an abdominal viscus 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 RADIOGRAPHSection 4 of 12
Findings
Degree of ConfidencePlain radiographic findings may be diagnostic in ill patients with diabetes who have signs of acute pyelonephritis. False Positives/NegativesRenal 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. CT SCANSection 5 of 12
FindingsCT is the examination of choice for diagnosing EPN.13, 16, 19
Degree of ConfidenceCT is the most reliable and sensitive modality in diagnosing EPN. False Positives/NegativesEPN 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. MRISection 6 of 12
FindingsMRI 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 ConfidenceMRI is not the modality of choice in the diagnosis of EPN. When CT is available, it should be used instead. False Positives/NegativesSignal voids on MRIs may occur with renal calculi or rapidly flowing blood. ULTRASOUNDSection 7 of 12
Findings
Degree of ConfidenceUltrasonography 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/NegativesGas 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 MEDICINESection 8 of 12
FindingsRadionuclide 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. INTERVENTIONSection 9 of 12
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 Medical/Legal Pitfalls
Related Medscape topic: ACKNOWLEDGMENTSSection 10 of 12
The authors and editors would like to acknowledge the contributions made to this article by Ramesh Chandra Raja, MBBCH, and Philip Wiles, MD. MULTIMEDIASection 11 of 12
REFERENCESSection 12 of 12
Emphysematous Pyelonephritis excerpt Article Last Updated: Jan 25, 2008 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
