Computed tomography (CT) plays a significant role in establishing the
diagnosis in clinically equivocal cases of renal infection, determinin
g 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 re
nal infection in order to demonstrate the areas of altered nephrogram
that occur as a result of the inflammatory process and to identify com
plications. In this article we review a spectrum of renal inflammatory
disease, with illustrations of the CT findings in representative case
s.We also review the role and potential pitfalls of fast scanning tech
niques 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 mul
tifocal hypodense areas with obliteration of the corticomedullary diff
erentiation. Delayed images obtained during the excretory phase are fr
equently more helpful in defining the extent of the disease process, i
dentifying the complications such as renal abscess, and confirming the
presence of urinary obstruction than are early images.