(Radiology. 2001;218:647-650.)
© RSNA, 2001
Emphysematous Pyelitis: Findings in Five Patients1
Catherine Roy, MD,
Dominique D. Pfleger, MD,
Christine M. Tuchmann, MD,
Hervé H. Lang, MD,
Christian C. Saussine, MD and
Didier Jacqmin, MD
1 From the Departments of Radiology (C.R., D.D.P., C.M.T.) and Urology (H.H.L., C.C.S., D.J.), Hôpitaux Universitaires de Strasbourg-Hôpital Civil, 1 place de l’hôpital, BP 426, 67091 Strasbourg, France. Received February 17, 2000; revision requested March 28; revision received June 19; accepted July 12. Address correspondence to C.R. (e-mail: catherine.roy@chru-strasbourg.fr).
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ABSTRACT
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Emphysematous pyelitis (EP) is a benign entity. To our knowledge, it has not been reported frequently in the radiology literature. Previous articles have not focused on EP but rather have included other gas-forming entities (eg, emphysematous pyelonephritis [EPN]). The authors describe imaging findings in EP and distinguish them from findings in EPN in five cases. Computed tomography is the current method for demonstrating isolated gas production inside the urinary collecting system. The prognosis is excellent, with rapid complete recovery after medical treatment.
Index terms: Kidney, CT, 81.12111, 81.12112, 81.12114, 81.12115 • Kidney, infection, 81.212, 81.214 • Nephritis, 81.212
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INTRODUCTION
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Emphysematous pyelonephritis (EPN) is a rare life-threatening suppurative renal infection characterized by gas formation within the renal parenchyma or perirenal tissues. We report five cases of a less severe variant called emphysematous pyelitis (EP). Our objective is to describe imaging findings in patients with this distinct clinical entity and distinguish them from findings in patients with EPN. EP is defined as isolated gas production inside the excretory system that is secondary to acute bacterial renal infection. To our knowledge, imaging findings in patients with EP have not been frequently reported in the literature; two articles (1,2) did not focus entirely on EP.
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Patient Information and Imaging Evaluation
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During the period of January 1998 to August 1999, five patients who had localized gas-producing bacterial renal infection were examined in our department. They included one man and four women, who ranged in age from 47 to 81 years.
All patients had a 1-week history of fever and chills at presentation. Unilateral upper-quadrant tenderness was on the right side in three patients and on the left side in two. Four patients had dysuria, and one had pyuria. Macroscopic hematuria was found in one patient (Table). In one patient, the medical history included poorly controlled diabetes mellitus. Two others had known calculus disease, and one had cirrhosis with portal hypertension. One patient had no pertinent medical history. At clinical survey in this patient, neither fistula between the urinary and bowel tract nor history of trauma or instrumentation in the urinary tract, including Foley catheter placement, was found. Laboratory tests revealed a normal serum creatinine level and negative blood cultures. All patients initially had urinary tract infection at presentation. Urinary organisms cultured were E coli (two patients), K pneumoniae (one patient), P mirabilis (one patient), and mixed flora (one patient). Glycosuria was present in one patient with an abnormal amount of red blood cells.
All patients underwent initial abdominal radiography and ultrasonography (US). Computed tomography (CT) was performed 12–36 hours after initial radiography and US. Spiral CT was performed by using a Somatom SR+ scanner (Siemens, Erlangen, Germany) with 3-mm collimation, a pitch of 1.5, and a total scanning time of 40 seconds. Images were reconstructed by using an interval of 3 mm and a standard algorithm. Two acquisitions were needed to evaluate the entire upper urinary tract. CT scans were obtained before and after intravenous administration of nonionic contrast material (iobiditrol [Xenetix 300; Lab Guerbet, Paris, France]). The quantity injected was 120 mL (injection rate, 3 mL/sec), with three phases of acquisition: early (30 seconds after injection), excretory (3 minutes after injection), and late (20 minutes after injection). This contrast medium injection later provided a good delineation of the foci of pyelonephritis. Each patient underwent gray-scale US (Elegra; Siemens) and CT again, with parameters similar to those used in the first examination, 3 weeks later. All images were reviewed by two radiologists (including C.R., D.D.P., and C.M.T.), and final decisions were reached with consensus.
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Imaging Findings and Follow-up
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All patients had abnormal imaging findings. Initial abdominal radiography revealed isolated retroperitoneal gas in one patient, ureteric stone in one, and retroperitoneal gas associated with ureteric stone in another. At US, we observed clean (distinct and echo-free) acoustic shadowing from the calyces in three patients and dirty (containing low-level echoes and reverberations) shadowing in two. One patient had upper urinary tract dilatation at presentation. At CT, gas-fluid levels were observed in cavities in all patients, and ureteric stones were observed in two.
At abdominal radiography, two patients had ureteric stones: one had staghorn calculi, and the other had a ureteric calculus. Gas bubbles were seen in the urinary collecting system in two patients. In the other three, they were hidden by overlying bowel gas. No gas was found in the ureter in any of the five patients. US revealed urinary tract dilatation in the patient with a ureteric stone. Shadowing from the calyces was interpreted as ureteric stones in three patients and as gas in two (Fig 1). In three patients, initial spiral CT depicted mild to large gas bubbles that were associated with gas-fluid levels in the dilated collecting system (Figs 1, 2). Only the ureteric lumbar stone caused obstruction. No gas was found in the renal parenchyma or perinephric area. Two patients had several small triangular parenchymal abnormalities that were typical for acute pyelonephritis (Fig 3). Treatment initially consisted of intensive intravenous antibiotic therapy. Clinical symptoms disappeared 1 day later. Urinary tract infection rapidly responded to antimicrobial therapy. The duration of intravenous treatment was 10 days. Patients were discharged while receiving oral antibiotics.
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Figure 1a. US and CT images in a 65-year-old woman with cirrhosis and portal hypertension in the right kidney. (a) Longitudinal US image shows large flat high-level echo (arrow) associated with distal shadowing. Dilatation of the calyces is obscured. (b) Initial transverse postcontrast CT scan shows the gas-fluid level (arrow) inside the dilated calyx. (c) Transverse postcontrast CT scan obtained at a level similar to that in b 3 weeks after medical treatment shows the disappearance of both gas and dilatation of the calyces. A normal fatty renal sinus is noted, as well as the remaining low-contrast attenuation of the parenchyma.
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Figure 1b. US and CT images in a 65-year-old woman with cirrhosis and portal hypertension in the right kidney. (a) Longitudinal US image shows large flat high-level echo (arrow) associated with distal shadowing. Dilatation of the calyces is obscured. (b) Initial transverse postcontrast CT scan shows the gas-fluid level (arrow) inside the dilated calyx. (c) Transverse postcontrast CT scan obtained at a level similar to that in b 3 weeks after medical treatment shows the disappearance of both gas and dilatation of the calyces. A normal fatty renal sinus is noted, as well as the remaining low-contrast attenuation of the parenchyma.
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Figure 1c. US and CT images in a 65-year-old woman with cirrhosis and portal hypertension in the right kidney. (a) Longitudinal US image shows large flat high-level echo (arrow) associated with distal shadowing. Dilatation of the calyces is obscured. (b) Initial transverse postcontrast CT scan shows the gas-fluid level (arrow) inside the dilated calyx. (c) Transverse postcontrast CT scan obtained at a level similar to that in b 3 weeks after medical treatment shows the disappearance of both gas and dilatation of the calyces. A normal fatty renal sinus is noted, as well as the remaining low-contrast attenuation of the parenchyma.
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Figure 2a. CT scans in a 47-year-old woman with poorly controlled diabetes in the right kidney. (a) Initial transverse postcontrast CT scan shows gas inside the renal pelvis (straight arrow) and calyces and a local zone of pyelonephritis (curved arrow) inside the parenchyma. (b) Transverse postcontrast CT scan obtained at a level similar to that in a 3 weeks later shows no gas inside the calyces and resolution of the pyelonephritis.
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Figure 2b. CT scans in a 47-year-old woman with poorly controlled diabetes in the right kidney. (a) Initial transverse postcontrast CT scan shows gas inside the renal pelvis (straight arrow) and calyces and a local zone of pyelonephritis (curved arrow) inside the parenchyma. (b) Transverse postcontrast CT scan obtained at a level similar to that in a 3 weeks later shows no gas inside the calyces and resolution of the pyelonephritis.
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Figure 3a. CT scans in a 72-year-old man with staghorn calculi in the left kidney. (a) Initial transverse postcontrast late-phase CT scan shows gas (arrow) inside the calyces and triangular high-attenuating zones (arrowheads) corresponding to focal pyelonephritis. The low-attenuating area in the posterior left kidney is a small cyst. (b) Transverse nonenhanced CT scan obtained at a level similar to that in a 3 weeks later shows no gas inside the calyces and a low-attenuating area in the left posterior kidney, which is a small cyst.
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Figure 3b. CT scans in a 72-year-old man with staghorn calculi in the left kidney. (a) Initial transverse postcontrast late-phase CT scan shows gas (arrow) inside the calyces and triangular high-attenuating zones (arrowheads) corresponding to focal pyelonephritis. The low-attenuating area in the posterior left kidney is a small cyst. (b) Transverse nonenhanced CT scan obtained at a level similar to that in a 3 weeks later shows no gas inside the calyces and a low-attenuating area in the left posterior kidney, which is a small cyst.
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At follow-up US and CT, there was neither evidence of gas in the collecting system nor hydronephrosis (Figs 1–3). No drainage procedures were needed. Ureteral stones were passed spontaneously before follow-up CT. The patient with staghorn calculi was treated 2 months later with percutaneous surgery.
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Discussion
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Gas in the urinary tract is a relatively rare occurrence that usually arises with urinary tract infection. Gas in the kidney is related to two clinical entities whose management and prognosis are different. One of these entities, EPN, is an uncommon life-threatening condition characterized by the production of gas within the renal parenchyma and perirenal space (1,2). It should be regarded as a severe necrotizing form of pyelonephritis. Several authors (1,2) have recommended that EPN be diagnosed only when gas has formed within the renal parenchyma. However, most authors define this entity as gas within the renal collecting system, parenchyma, and perirenal spaces.
Investigators in a recent study (1) defined two types of EPN on the basis of radiologic findings. Type I is characterized by parenchymal destruction with either absence of fluid or fluid collection or by the presence of streaky or mottled-appearing gas. Type II is characterized by either renal or perirenal fluid collection with bubbly or loculated gas or gas in the collecting system. The presence of gas in the renal parenchyma, collecting system, or perinephric space may have substantial prognostic and therapeutic implications (1–4). Type I may represent classic EPN, which has a high reported mortality rate (69%), as noted in the radiology and urology literature (1,2,4). In the study by Joseph et al (2), gas in the renal pelvis and ureter was found only in patients with type II EPN, in which the prognosis is favorable, with a mortality rate of 18%. More than 90% of all types of EPN occur in patients with diabetes mellitus.
EP is a term representing gas-forming urinary tract infection that is associated with gas localized in only the renal collecting system. This entity is cited in radiology books and is associated with diabetes mellitus and obstruction of the collecting system (1). However, to our knowledge, only two isolated cases have been described as case reports in the literature (1,2).
E coli is the most common infecting organism in patients with EPN (70%), followed by K pneumoniae (24%), Aerobacter aerogenes (10%), P mirabilis (5%), and mixed or other flora. The cause of gas formation (carbon dioxide and hydrogen) in patients with EPN is not well understood. One proposal is that gas is formed at mixed acid fermentation of a glucose-rich substrate (5,6) in patients with severe necrotizing infections. The resultant necrotic tissue may then act as a substrate for gas formation, and the gas then becomes entrapped by an obstructive process. The pathogenesis probably involves several factors that result in pyelonephritis becoming an emphysematous condition: gas-forming bacteria, enhanced proliferation of microorganisms because of altered immune defenses, vascular impairment with ischemia or infarct, and high tissue glucose concentration (7–11). Gas formation can be rapid (11), and the continued presence of gas indicates active infection and ineffective antimicrobial therapy.
The diagnosis of EP is often delayed because the clinical manifestation may be nonspecific, as illustrated by the patients in the current study, similar to the clinical presentation of uncomplicated acute pyelonephritis. On radiographs, the manifestation of this disorder is similar to findings on gas pyelograms, with gas outlining the pelvocaliceal system. The gas may be present in the ureters and on rare occasions associated with cystitis emphysematosa (12). Although abdominal radiography usually allows easy detection of air, the sensitivity reported with radiography is low (33%) (10,11). This is due to difficulty in differentiating renal gas from air in overlying loops of bowel.
In patients with diabetes and febrile urinary tract infection, US is recommended for detecting urinary tract obstruction. The typical US appearance of gas-producing renal infections is that of high-amplitude flat anterior margin echoes within the renal sinus or calyces, which are associated with distal shadowing containing low-level echoes and reverberations. In theory, this dirty shadowing can be differentiated from the more distinct echo-free clean acoustic shadowing that occurs distal to renal calculi. US provides less specific information about gas-producing renal infection because of potential confusion with either air or renal calculi or calcifications within the kidney. In practice, confusion is possible and US images may be interpreted variably. In our opinion, CT is the most reliable diagnostic imaging modality currently available for this purpose. Ureteric stones are precisely evaluated and differentiated from intracaliceal, intrapelvic, or perinephric gas collections. CT is sensitive and essential in demonstrating and precisely localizing air within the caliceal system and eliminating air within the kidney parenchyma and/or pararenal spaces. CT allows both accurate diagnosis and staging.
Indeed, EP should be differentiated from the reflux of air or gas from the bladder or from ileal ureterosigmoidostomy. The spontaneous appearance of gas within the upper urinary tract has three main origins: iatrogenic manipulation (ie, ureteral instrumentation, surgical or interventional radiologic procedure), fistulous connection with a hollow viscus, or bacteria caused by reflux from the bladder.
The prognosis and clinical management of EP and EPN are different. As opposed to EPN, EP is reported as a benign condition. Intraparenchymal gas usually requires drainage or nephrectomy and is associated with a substantial mortality rate, whereas EP is associated with a low overall mortality rate. If gas is localized to the collecting system and no obstruction is present, antibiotic therapy alone appears to be sufficient. CT can depict the complete resolution of air and dilatation of cavities. This differentiation between types of gas-forming renal infection is important because of the prognostic difference. In our opinion, CT is the most reliable imaging modality for depicting this abnormality.
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FOOTNOTES
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Abbreviations: EP = emphysematous pyelitis,
EPN = emphysematous pyelonephritis
Author contributions: Guarantor of integrity of entire study, C.R.; study concepts and design, C.R.; definition of intellectual content, D.J.; literature research, C.M.T.; clinical studies, H.H.L.; data acquisition, C.M.T.; data analysis, D.D.P.; statistical analysis, C.R.; manuscript preparation and editing, C.R.; manuscript review, C.C.S.
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Wan YL, Lee TY, Bullard MJ, Tsai CC. Acute gas-producing bacterial renal infection: correlation between imaging findings and clinical outcome. Radiology 1996; 198:433-438.[Abstract/Free Full Text]
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TOP
ABSTRACT
INTRODUCTION
