Abstract
This work aims to evaluate whether radiological signs of stone impaction (RSSI) measured on non-contrast computed tomography (CT) can predict shock wave lithotripsy (SWL) outcomes for upper ureteral stones and to assess whether integrating these markers into an existing prediction model (the Niwa nomogram) improves predictive performance. We retrospectively analysed 256 patients treated with SWL for upper ureteral stones between 2012 and 2019. Standard stone parameters and RSSI, including ureteral wall thickness (UWT), ureteral diameters and CT attenuations above and below the stone, were assessed. Multivariable logistic regression, receiver operating characteristic (ROC) analysis, net reclassification improvement (NRI) and decision curve analysis (DCA) were used to evaluate predictive performance. The Niwa nomogram was enhanced by incorporating significant RSSI parameters and was internally validated using k-fold cross-validation. Maximum ureteral attenuation below the stone (UABSmax), ureter diameter above the stone (UDAS) and renal pelvis diameter (RPD) were found to be associated with SWL outcome. UABSmax had the highest individual predictive value (area under the curve (AUC) 0.66), while UWT showed no significant association or predictive value. Incorporating UABSmax and RPD into the Niwa nomogram (Niwa+) marginally increased AUC (0.72 vs. 0.71) but did not lead to significant improvements in NRI or DCA. In conclusion, certain RSSI- particularly UABSmax and RPD- were associated with SWL outcome but provided limited value when added to an already validated nomogram.