Urinary Tract Infection Acute Pyelonephritis

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Acute pyelonephritis is usually an ascending infection spread from the bladder, and is seen predominately in females. Rarely, the source of infection is hematogenous bacteremia. Diagnosis is usually made on clinical grounds and with urine analysis. Imaging may be needed to detect complications or sequela of pyelonephritis. When clinical pyelonephritis persists for greater than three days after antibiotic therapy has been initiated, then imaging is recommended. CT is the imaging technique of choice to evaluate the kidneys for possible complications of pyelonephritis, such as abscess or obstruction. CT is the most sensitive and specific test for detecting the changes of acute pyelonephritis and its complications. Typical CT findings of pyelonephritis include unilateral nephromegaly, renal striations, wedge-shaped defects, and perinephric inflammatory changes [20]. Areas of liquefaction within the renal parenchyma indicate the development of a renal abscess. CT is more sensitive for the detection of renal abscess than other techniques, such as IVU or US.

In males with a urinary tract infection (UTI) and/or suspected pyelonephritis, US is valuable to identify common causes of UTI such as epididymitis, orchitis and prostatitis. Patients with a neurogenic bladder secondary to a spinal cord injury pose a difficult problem as the urine is usually colonized. Development of systemic symptoms should prompt rapid imaging as these patients may not be sensate to pain and a devastating abscess can develop quickly [21]. Finally, in order to diminish radiation dose to pregnant patients, US with power Doppler may be at tempted prior to CT to detect areas of aberrant blood flow. This has been shown to be useful in children [22, 23].

Sequela of pyelonephritis includes changes of reflux nephropathy. These changes include renal scarring and calyceal blunting due to reflux of urine through the ducts of Bellini, resulting in parenchymal scarring. Changes of reflux nephropathy include broad-based scars centered over clubbed calyces, predominately occurring in the poles of the kidneys. Overall renal function of the affected kidney is best evaluated with radionuclide renography.

Emphysematous Pyelonephritis

This life-threatening infection with a gas-producing organism has a mortality rate of up to 90% without nephrectomy. The infection is usually caused by a strain of E. coli in diabetic patients. The diagnosis of emphysematous pyelonephritis is made when gas is seen in the renal parenchyma. CT is the most accurate technique for diagnosing emphysematous pyelonephritis and for differentiating this entity from emphysematous pyelitis or perinephric emphysematous infections. CT is also most accurate for differentiating localized from diffuse emphysematous pyelonephritis. Localized emphysematous pyelonephritis has been successfully treated with percutaneous drainage in combination with systemic antibiotic management.

Granulomatous Renal Infections

Tuberculosis, xanthogranulomatous pyelonephritis (XGP), malacoplakia, and fungal infections can all affect the urinary tract. Renal tuberculosis is usually spread hematogenously from the lungs seeding the kidneys. Symptomatic renal tuberculosis results from secondary, reactivation tuberculosis. Symptoms typically include hematuria and sterile pyuria. The earliest signs of renal tuberculosis include focal papillary necrosis and inflammation of the calyces. With progression, areas of fibrosis and calcification may develop. Long-standing tuberculosis may result in numerous fibrotic strictures, ureteral wall thickening, hydronephrosis, and autonephrectomy.

XGP, an inflammatory condition with a marked female predominance, is associated with recurrent UTIs caused by proteases, or E. coli bacteria. An infection-based stone is seen in the majority of cases. The classic radiographic triad includes reniform enlargement of the kidney, a renal stone, and markedly decreased or absent renal function in the affected kidney. Localized XGP occurs in 20% of cases and can mimic renal neoplasms on imaging studies [24].

Both malacoplakia and fungal infections have nonspecific appearances. They are often multifocal, but a tissue diagnosis is required to exclude neoplasm. A feature of malacoplakia is congregated histiocytes. It is more commonly seen in the bladder and ureter than the kidney. The microscopic hallmark of malacoplakia is the Michaelis-Gutman inclusion body seen within the abnormal histio-cytes. When malacoplakia involves the ureter or bladder, multiple submucosal masses are usually identified.

Imaging findings are nonspecific and tissue is required for definitive diagnosis. Fungal infections are usually seen in immunocompromised patients, including diabetics. Debris, often present within the renal collecting system forms a 'hand-in-glove' filling defect of the contrast-opacified calyces.

AIDS Nephropathy

Autoimmune deficiency syndrome (HIV/AIDS) nephropathy constitutes a variety of renal pathologies. Findings are generally nonspecific, but patients with an HIV infection, renal failure, and hyperechoic nephromegaly likely have AIDS nephropathy. These sonographic findings in an AIDS patient usually indicate that the patient will develop irreversible renal failure.

Pyonephrosis

Pyonephrosis constitutes a bacterial infection of the urine associated with ureteral obstruction. If untreated, this can lead to rapid demise and irreversible damage to the kidney, and septicemia. Pyonephrosis is best diagnosed with US. Any febrile patient with hydronephrosis should be suspected of harboring pyonephrosis. Other findings that suggest pyonephrosis include echogenic urine, and debris within the hydronephrotic calyces. Prompt urinary tract drainage, preferably using percutaneous nephrostomy techniques, is required for treatment of pyonephrosis. This is accompanied by systemic antibiotic administration.

Schistosomiasis

Schistosomiasis of the urinary tract is caused by infection with Schistosoma hematobium. This parasite is endemic in Egypt. The infection usually arises in the bladder, but may spread to the ureters and kidneys via reflux to the upper tracts. Dystrophic calcifications in the wall of the bladder and ureter are typical findings and are caused by calcification of the dead ova. Typical radiographic findings include mural calcifications, ureteral strictures, and vesicoureteral reflux. These patients have a markedly increased risk for development of squamous cell carcinoma of the urinary tract.

Ureteral Pseudodiverticulosis

This uncommon abnormality is caused by overgrowth of the urothelial lamina propria. Although cellular atypia is commonly seen in association with ureteral pseudodiver-ticulosis, it is thought to be a benign lesion. However, the presence of ureteral pseudodiverticulosis should be considered a warning sign for the development of transitional cell carcinoma. There appears to be high risk of synchronous transitional cell carcinomas, or later development of transitional cell carcinoma in the urothelial field affected by the pseudodiverticulosis. Close radiographic follow-up is warranted in these patients.

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