CT of renal inflammatory disease.

Although computed tomography (CT) is not routinely indicated in uncomplicated renal infection, it is of value in establishing the diagnosis in equivocal cases, in evaluating high-risk patients, and in determining the extent of disease. Unenhanced CT is useful in demonstrating gas, calculi, parenchymal calcifications, hemorrhage, and inflammatory masses. However, a contrast material-enhanced study is essential for complete evaluation of patients with renal inflammatory disease to demonstrate alterations in renal excretion of contrast material that occur as a result of the inflammatory process. In severe acute pyelonephritis, enhanced CT scans obtained during the cortical nephrographic phase typically demonstrate solitary or multifocal areas of hypoattenuation with loss of the corticomedullary interface. Delayed CT scans obtained during the excretory phase are frequently more helpful than early CT scans in defining the extent of the disease process, identifying complications such as renal abscess, and confirming the presence of urinary obstruction.