Predicting the Outcome of Renal Stones Treated by Shock Wave Lithotripsy on the Basis of CT Morphodensitometry

Background: Shock wave lithotripsy (SWL) is a non-invasive treatment for selected renal calculi, but treatment success varies according to stone and renal anatomical characteristics. Computed tomography (CT) provides objective information on stone density and collecting-system anatomy that may improve prediction of SWL outcome. The objective is to evaluate the utility of CT urography/CT morphodensitometry in predicting the outcome of SWL for renal stones, with particular emphasis on Hounsfield unit (HU) density, stone size, location, infundibulum length, and infundibulopelvic angle. Material and Methods: This hospital-based prospective observational study was conducted in the Department of Urology, Pt. B.D. Sharma PGIMS, Rohtak, from January 2024 to December 2025. Adults with renal stones up to 20 mm who were suitable for SWL were enrolled consecutively. Pre-treatment CT urography/CECT KUB was used to assess stone size, location, density, infundibulum length and infundibulopelvic angle. SWL was delivered using an electromagnetic lithotripter, with a maximum of 3000 shocks per session. Success was defined as stone-free status or residual fragments <4 mm after treatment; residual fragments ≥4 mm after three sessions or need for ancillary stone-removal procedures was considered failure. Univariate analysis, ROC analysis and backward stepwise multivariable logistic regression were performed. Results: Among 100 patients, 79 (79.0%) achieved successful SWL and 21 (21.0%) failed. Mean stone size was 12.82 ± 4.24 mm and mean stone density was 717.83 ± 209.56 HU. On univariate analysis, sex (P=0.036), stone location (P=0.036), calyceal versus non-calyceal location (P=0.001), stone density (P=0.001), infundibulum length (P=0.015 for categorical analysis; P=0.006 for mean comparison), and infundibulopelvic angle (P=0.005 for categorical analysis; P=0.035 for mean comparison) were associated with outcome. Age, stone size, number of sittings and number of shocks were not significant. ROC analysis showed the greatest discriminatory ability for stone density, with an AUC of 0.926 (95% CI 0.847–0.999; P=0.001) at an optimal cut-off of 775 HU. On multivariable analysis, non-calyceal location (OR 2.966, 95% CI 1.487–6.889; P=0.013) and stone density <800 HU (OR 7.748, 95% CI 3.794–23.448; P=0.001) remained independent predictors of success. Overall, 21% of patients experienced a recorded complication, most commonly hematuria (8%), Steinstrasse (7%) and pain (6%). Conclusion: CT morphodensitometry provides clinically useful information for predicting SWL outcome. Stone density was the strongest predictor, followed by stone location. Patients with lower-density and non-calyceal stones were more likely to achieve successful SWL. CT-derived anatomical parameters may provide additional information for patient selection, although their independent predictive value was not retained after multivariable adjustment. Keywords: Renal Calculi, shock wave lithotripsy, SWL, computed tomography, CT morphodensitometry, Hounsfield units, stone density, infundibulopelvic angle.