Acute ureterolithiasis: Nonenhanced helical CT findings of perinephric edema for prediction of degree of ureteral obstruction

PURPOSE: To determine whether the extent of perinephric edema on helical computed tomographic (CT) images without contrast material enhancement can be used to predict the degree of ureteral obstruction in patients with acute ureterolithiasis. MATERIALS AND METHODS: Nonenhanced helical CT and excretory urographic images in 82 patients with flank pain were retrospectively reviewed. For each patient, a radiologic diagnosis was established, and the degree of ureteral obstruction determined on urograms was compared with the extent of perinephric edema assessed on CT images. RESULTS: None of 29 patients with no abnormalities seen at urography had evidence of perinephric edema at CT. Of six patients with noncalculous disease, two with acute pyelonephritis had perinephric edema at CT. Of 47 patients with acute ureterolithiasis, eight had no perinephric edema at CT and a nonobstructing calculus at urography, 21 had limited edema at CT and low-grade obstruction at urography, and 15 had extensive edema at CT and high-grade obstruction at urography. Three patients had extensive perinephric edema at CT but low-grade obstruction at urography. The extent of edema allowed accurate prediction of the degree of ureteral obstruction in 44 (94%) of 47 patients with acute ureterolithiasis. CONCLUSION: The extent of perinephric edema on nonenhanced helical CT images can be used to predict the degree of ureteral obstruction in acute ureterolithiasis.