Figure 729

Computed tomodensitometry. Simple pyelonephritis does not require much imaging; however, it should be remembered that there is no correlation between the severity of the clinical picture and the renal lesions. Therefore, a diagnosis of "simple" pyelonephritis at first contact can be questioned when response to treatment is not clear after 3 or 4 days. This is an indication for uroradiologic imaging, such as renal tomodensitometry followed by radiography of the urinary tract while it is still opacified by the contrast medium.

The typical picture of acute pyelonephritis observed after contrast medium injection [10] consists of hypodensities of the infected areas in an edematous, swollen kidney. The pathophysiology of hypodense images has been elucidated by animal experiments in the primates [11] which have shown that renal infection with uropathogenic Escherichia coli induces intense vasoconstriction.

Computed tomodensitometric images of acute pyelonephritis can take various appearances. The most common findings consist of one or several wedge-shaped or streaky zones of low attenuation extending from papilla to cortex, A. Hypodense images can be round, B. On this figure, the infected zone reaches the renal cortex and is accompanied with adjacent perirenal edema. Several such

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