CT-based determination of maximum ureteral stone area: a predictor of spontaneous passage.

OBJECTIVE: The purpose of this study was to test the hypothesis that the maximum axial area of ureteral stones is a more accurate predictor of spontaneous passage than the maximum axial diameter.
MATERIALS AND METHODS: This study retrospectively reviewed 211 consecutive emergency department patients (mean age, 48.8 years; age range, 18-88 years) with acute flank pain due to ureteral stones diagnosed using unenhanced CT. Measurements of maximum atrial area were obtained using fixed (FTM) and variable (VTM) threshold methods. For the FTM, stones were segmented using an attenuation threshold of 130 HU. For the VTM, stones were segmented using an attenuation threshold determined by one half of individual stone attenuation. Measurements of maximum atrial diameter were obtained using soft-tissue and bone window settings. Receiver operating characteristic (ROC) analysis was used to compare the accuracy of maximum atrial area with maximum atrial diameter measurements for predicting spontaneous passage.
RESULTS: Fifty-seven patients (27%) required urologic intervention. The areas under the ROC curve (AUC) of maximum atrial area using FTM (0.83, p = 0.013) and VTM (0.84, p = 0.004) were larger than the AUC (0.8, p = 0.4) for maximum atrial diameter using bone window settings or AUC (0.79) for maximum atrial iameter using soft-tissue window settings. For stones with maximum atrial diameter (in soft-tissue window settings) > 5 mm and ≤ 10 mm, the accuracy of maximum atrial area using VTM (AUC = 0.75) and FTM (AUC = 0.74) was superior to the accuracy of maximum atrial diameter in soft-tissue (AUC = 0.67) and bone (AUC = 0.69) window settings (p < 0.05) in predicting spontaneous passage.
CONCLUSION: Determination of the maximum axial area may improve the accuracy in predicting spontaneous passage of ureteral stones, particularly those between 5 and 10 mm.