Renal inflammatory disease: the current role of CT

Computed tomography (CT) plays a significant role in establishing the diagnosis in clinically equivocal cases of renal infection, determining the extent of the disease process, and assessing its complications. Gas, calculi, renal parenchymal calcifications, hemorrhage, and masses can be revealed with unenhanced CT. A subsequent study with contrast enhancement is crucial for the complete evaluation of patients with renal infection in order to demonstrate the areas of altered nephrogram that occur as a result of the inflammatory process and to identify complications. In this article we review a spectrum of renal inflammatory disease, with illustrations of the CT findings in representative cases. We also review the role and potential pitfalls of fast scanning techniques that can image a particular phase of the nephrogram in a renal infection. In acute pyelonephritis, enhanced CT scans obtained during the cortical nephrographic phase typically demonstrate solitary or multifocal hypodense areas with obliteration of the corticomedullary differentiation. Delayed images obtained during the excretory phase are frequently more helpful in defining the extent of the disease process, identifying the complications such as renal abscess, and confirming the presence of urinary obstruction than are early images.