Emphysematous pyelonephritis (EPN) is a severe, necrotizing infection of the renal parenchyma; it causes gas formation within the collecting system, renal parenchyma, and/or perirenal tissues (see the image below.) Other terms that have been used to describe the condition include renal emphysema and pneumonephritis. Gas in the renal pelvis alone, without parenchymal gas, is often referred to as emphysematous pyelitis. (See Etiology.)
EPN most often occurs in persons with diabetes mellitus, especially women. Its presentation is similar to that of acute pyelonephritis (see Presentation). However, the clinical course of EPN can be severe and life-threatening if the disease not recognized and treated promptly.
Since the first description of EPN, in 1898,  approximately 300 cases of EPN have been reported. Although most information on the disease has come from case reports, a few large series have also been published. This article describes the pathogenesis, classification, complications, and management of EPN based on a review of seven series featuring a total of 226 patients. [2, 3, 4, 5, 6, 7, 8]
Although nephrectomy may be the quickest way of treating the infection source, renal function is compromised in many patients; therefore, a strategy to preserve nephrons may be very desirable. The above-mentioned series highlight such an approach, reserving nephrectomy for patients in whom conservative treatment does not elicit a response. (See Treatment.)
Management is based on the clinical and laboratory findings. If the patient is stable, conservative treatment with antibiotics and drainage should be tried.  If the patient has gas in the renal parenchyma and perinephric tissues along with significant exudate, initial percutaneous drainage should be given a chance. Saving nephrons and the patient's life should be weighed based on the clinical situation, response to treatment, and available facilities. (See Workup and Treatment.)
For patient education information, see Urinary Tract Infections (UTIs).
Emphysematous pyelonephritis (EPN) is a severe infection of the renal parenchyma that causes gas accumulation in the tissues. The infection, which in some cases occurs bilaterally, often has a fulminating course and can be fatal if left untreated. However, urinary tract infections are common in persons with diabetes, and not all of these infections lead to EPN.
The factors that predispose persons with diabetes to EPN may include uncontrolled diabetes, high levels of glycosylated hemoglobin, and impaired host immune mechanisms. In 1993, Guiard proposed alcoholic fermentation of glucose with carbon dioxide production by the organisms as the cause of gas in the tissues.
In 1889, Muller first identified nitrogen, hydrogen, and carbon dioxide in a patient with pneumaturia. Schainuck et al proposed that fermentation products from tissue necrosis produced carbon dioxide.  Three investigators analyzed the gas content, and all 3 demonstrated that the major components of the gas in EPN include nitrogen (60%), hydrogen (15%), carbon dioxide (5%), and oxygen (8%).
Huang et al concluded that mixed acid fermentation is the mechanism of gas production based on the presence of hydrogen.  Yang and Shen indicated that gas-forming infections depend on rapid tissue catabolism and impaired transport of the end products at the inflammatory site. 
Although carbon dioxide is released by the bacteria, the final tissue equilibrium achieved by tissues and gas bubbles determines the final carbon dioxide content. Diabetic microangiopathy may also contribute to the slow transport of catabolic products and may lead to accumulation of gas.
Transplanted kidneys may be susceptible to EPN because of associated high-risk factors in the recipient, such as diabetes and immunosuppression.  Renal stones also predispose patients to EPN.
Among the bacteria associated with emphysematous pyelonephritis (EPN), Escherichia coli is isolated in 66% of patients, and Klebsiella species are reported in 26% of patients. Proteus,Pseudomonas, and Streptococcus species are other organisms found in patients with EPN, and Entamoeba histolytica and Aspergillus fumigatus also have been reported to cause the disease. Mixed organisms are observed in 10% of patients. Positive blood culture results are identical to urine culture results in 54% of patients. Rare organisms such as Clostridium and Candida species have also been isolated in patients with EPN.
The mean age of patients with emphysematous pyelonephritis (EPN) is reportedly 55 years, with a range of 19-81 years. The condition is 6 times more common in women. Ninety-five percent of patients have diabetes. In most patients, the diabetes is uncontrolled, with high levels of glycosylated hemoglobin (72%) or of blood sugar.
Rare cases have been reported in persons who do not have diabetes, with renal failure and immunosuppression as contributing factors. Of these patients, 22% have obstructed upper tracts, 4% have polycystic kidneys, and 4% have end-stage renal disease. Obstruction is the main cause of EPN in persons without diabetes. The left kidney is affected more commonly than the right. Bilateral cases have also been reported.
EPN is a rare condition. Only 1-2 cases per year are encountered in a typical, busy urologic department in the United States. However, the frequency of reports from developing nations suggests that this may be a reflection of access to health care and health education. Because the condition preferentially affects persons with diabetes, the reported frequency reflects how poorly diabetes is controlled in these geographical areas. Renal stones are another predisposing condition and therefore affect the frequency of EPN.
Untreated cases of emphysematous pyelonephritis (EPN) result in death. The mortality rate associated with the disease was high before the advent of antibiotics; however, advances in imaging technology, diabetes control, resuscitative management, and minimally invasive treatment have improved patient outcomes.
Huang and Tseng reported an overall EPN mortality rate of 19%.  They also reported significant treatment success rates with percutaneous drainage and antibiotics (66%) and with nephrectomy (90%).
Wan et al reported a mortality rate of 40%.  Furthermore, the investigators reported a high risk of death in patients with serum creatinine levels greater than 1.4 mg/dL and platelet count of less than 60,000/μL.
Medical treatment of EPN may lead to uncontrollable sepsis that requires surgical intervention. Perinephric abscess and renal failure are other possible complications. Nephrectomy complications include injury to the colon, duodenum, and great vessels. Postoperative wound infection is common, because wound healing in these patients is compromised.
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