Soft-tissue ''rim'' sign in the diagnosis of ureteral calculi with use of unenhanced helical CT

PURPOSE: To determine the value of the ureteric soft-tissue ''rim'' sign for differentiation of ureteral calculi from phleboliths on unenhanced helical computed tomographic (CT) scans and to identify factors that are associated with the presence of the rim sign. MATERIALS AND METHODS: Of 442 patients with ureteral obstruction confirmed at CT, 200 had documented ureteral stone disease; 136 of these patients had ureteral calculi, excluding the ureterovesical or ureteropelvic junctions. Each calculus and phlebolith along the course of the meter were evaluated retrospectively and blindly for the presence of the rim sigh, stone location, and stone size; the duration of symptoms was documented when available. RESULTS: The rim sign was present in 105 of 136 ureteral calculi (77%) and in 20 of 259 phleboliths (8%) and yielded a sensitivity of 77% and a specificity of 92% for distinguishing a calculus from a phlebolith. Calculi associated with the rim sign had a mean size of 4.3 mm, and calculi without a rim sign had a mean size of 6.3 mm (P < .001). There was no difference in duration of symptoms among patients who did or did not exhibit a rim sign. CONCLUSION: In patients with flank pain the presence of a rim sign is a strong indicator that a calcification along the course of the ureter is a stone. Absence of the rim sign indicates that a calcification remains indeterminate.