Emphysematous Pyelonephritis

Clinical Emphysematous pyelonephritis is not a separate entity, but a severe type of necrotizing pyelonephritis. The criteria for defining this condition are not settled; some authors define emphysematous pyelonephritis only if gas is found within renal parenchyma, while others expand the definition and include gas not only within the parenchyma but also in the excretory system and perirenal spaces. Emphysematous pyelonephritis should be differentiated from emphysematous pyelitis; the latter is a generally benign condition consisting of gas in the urinary collecting system.
Emphysematous pyelonephritis develops mostly in diabetic patients, both insulin and non–insulin dependent. Concomitant urinary obstruction is more common in nondiabetics. It is a rapidly progressive, life-threatening infection associated with gas-forming coliform bacteria such as Escherichia coli and others. It is almost always unilateral. The simultaneous occurrence of emphysematous pyelonephritis and emphysematous cholecystitis is rare. Gas is located in the renal parenchyma, perirenal tissues, and at times the collecting system.
Imaging In spite of some authors’ opinion that a diagnosis of emphysematous pyelonephritis should be made by CT, quite often conventional radiography
is sufficient to detect this condition. Thus in patients with emphysematous pyelonephritis diagnosed by CT, abnormal gas was identified with conventional radiography in 66% and US in 88%. When localized, emphysematous pyelonephritis can mimic an abscess. Emphysematous pyelonephritis generally is not associated with ureteral obstruction. The imaging appearance of emphysematous pyelonephritis consists of either parenchymal destruction with absence of fluid or the presence of streaky or mottled gas, or it contains either renal or perirenal fluid and bubbly or loculated gas or collecting system gas. Such differentiation appears to be of prognostic importance because the former patients have a more fulminant course.
Radiology images of emphysematous pyelitis. A: Ultrasonography in a woman with cirrhosis and portal hypertension reveals hyperechoic structures with distal shadowing (arrows) in the right kidney. B: Transverse postcontrast CT identifies a gas-fluid level in a dilated calix (arrow). Follow-up CT 3 weeks after therapy revealed a normal appearing right kidney.

Although some of these patients respond to medical management,many undergo a nephrectomy. Some have been successfully treated with imaging-guided percutaneous drainage, but such drainage is not feasible with diffuse
involvement. Some drained patients subsequently require elective nephrectomy for adequate therapy. The serum creatinine level is the most reliable predictor of outcome. Affected kidneys tend to recover function after medical therapy, although many of these patients with underlying diabetes already suffer from chronic renal failure.

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