What is the imaging appearance of infections in the urinary tract?
Mild or initial episodes of acute pyelonephritis cause no permanent sequelae in the kidneys. Imaging is not indicated in clinically suspected acute pyelonephritis or in UTIs limited to the bladder. In patients with acute pyelonephritis who do not respond to appropriate antibiotic therapy, contrast-enhanced CT may be helpful to evaluate for complications such as a renal or perirenal abscess. CT is more sensitive than US in showing the presence and extent of complications. In patients who cannot receive iodinated contrast material, MRI may be performed as a good alternative.
With recurrent episodes of severe pyelonephritis, scarring may occur in the kidneys, and the calyces underlying the areas of scarring may be blunted or deformed. Urography may show a congenital abnormality or an obstructive lesion such as a stricture that may be contributory to the refractory UTI. In patients with VUR, the renal parenchymal scarring is most marked in the poles of the kidneys, with the upper pole of the kidney being the most severely affected.
Tuberculosis of the urinary tract usually is secondary to pulmonary tuberculosis and is seen commonly in areas of the world where this infection is prevalent. The process starts in the renal papilla, where cavitary changes may be seen. Presence of strictures in the infundibula of the collecting system and renal parenchymal calcifications clinch the diagnosis. The caseating tuberculous granulomas calcify, and if untreated, they eventually involve the entire kidney. An end-stage tuberculous kidney becomes calcified and atrophic and is referred to as a “putty” kidney. The process can descend to the ureters and urinary bladder causing strictures. Tuberculosis in the bladder results in a very small capacity, poorly distensible, and scarred bladder, known as a “thimble” bladder.
Schistosomiasis is an infection endemic in many parts of the world. The urinary tract is affected by S. haematobium , and heavy calcification is typically seen in the bladder. The bladder remains of normal capacity and distensible, unlike that involved by tuberculosis. The infection can ascend to involve the ureters, which can develop calcifications in the walls along with strictures. The calcifications in the urinary tract are best demonstrated on CT.