Computed tomographic (CT) findings of 17 pyonephrotic and 20 uninfected hydronephrotic kidneys were reviewed. Parameters evaluated included: renal pelvic wall thickness (none; grade 1, < or = 2 mm; grade 2, 3-5 mm; and grade 3, > 5 mm), renal pelvic contents, parenchymal, and perirenal findings. All patients underwent subsequent percutaneous nephrostomy within 1 week of CT. Common CT findings suggesting pyonephrosis include increased pelvic wall thickness and more severe perirenal fat changes than are seen in uninfected hydronephrosis. However, for any one patient, these findings are often not diagnostic. The presence of clinical signs of infection with hydronephrosis on CT is a more sensitive indicator of pyonephrosis than most CT findings.

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