Plain abdominal x-ray versus computerized tomography screening: Sensitivity for stone localization after nonenhanced spiral computerized tomography

Purpose: Urolithiasis followup with plain abdominal x-ray requires adequate visualization of the calculus on the initial x-ray or computerized tomography (CT) study. We compared the sensitivity of plain abdominal x-ray versus CT for stone localization after positive nonenhanced spiral CT. Materials and Methods: We evaluated 46 consecutive nonenhanced spiral CT studies positive for upper urinary tract lithiasis for which concurrent plain abdominal x-rays were available. X-ray and CT studies were compared for the ability to visualize retrospectively a stone given its location by CT. A consensus of 1 radiologist and 3 urologists was reached in each case. Cross-sectional stone size and maximum length were measured on plain abdominal x-ray, Results: Plain abdominal x-ray and scout CT had 48% (22 of 46 cases) and 17% (8 of 46) sensitivity, respectively, for detecting the index stone (p (0.00004). Of the 39 stones overall visualized on plain abdominal x-ray only 19 (49%) were visualized on scout CT. Mean cross-sectional area and length of the stones on scout CT were 0.34 cm.(2) (approximately 6 X 5.5 mm.) and 6.5 mm,, respectively, while the average size of those missed was 0.11 cm.(2) (approximately 4 x 3 mm.) and 3.6 mm. The mean size differences in the groups were highly significant (p (0.0009). Conclusions: Plain abdominal x-ray is more sensitive than scout CT for detecting radiopaque nephrolithiasis, Of the stones visible on plain abdominal x-ray 51% were not seen on CT. To facilitate outpatient clinic followup of patients with calculi plain abdominal x-ray should be performed when a stone is not clearly visible on scout CT.