Comparative predictive value of 3D stone volume versus maximal diameter for retrograde intrarenal surgery success: a prospective clinical analysis

Kemal Ertaş^1,*, Ali Yasin Özercan²
1 Department of Urology, Memorial Dicle Hospital, Diyarbakir, Turkey
2 Department of Urology, Kayseri City Education and Research Hospital, Kayseri, Turkey
* Corresponding Author: Kemal Ertaş. Email: email
(This article belongs to the Special Issue: Urolithiasis in Focus: Integrated Perspectives on Infection, Metabolic Dysfunction, and Contemporary Management)

Canadian Journal of Urology https://doi.org/10.32604/cju.2026.070210

Received 10 July 2025; Accepted 26 March 2026; Published online 06 July 2026

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Abstract

Objective: Retrograde intrarenal surgery (RIRS) is a widely adopted minimally invasive procedure for renal stones, yet accurately predicting its success remains challenging. This study aimed to evaluate the predictive value of three-dimensional (3D) stone volume compared with traditional maximal stone diameter for RIRS success and complications. Methods: This prospective single-center study included 122 patients undergoing RIRS for renal calculi. Preoperative non-contrast CT scans were used to measure stone volume using the ellipsoid formula. Surgical outcomes included stone-free rate (SFR; residual fragments ≤2 mm) and complications (Clavien-Dindo classification). Receiver operating characteristic (ROC) curves, DeLong’s test, and multivariable logistic regression were performed. Non-parametric tests were used for skewed data. Results: Median stone size was 16 mm (IQR 12–22) and median stone volume was 2357 mm³ (IQR 628–5124). The stone-free rate was 66.4% (81/122). Successful cases had significantly smaller median stone size [14 mm (IQR 11–18) vs. 21 mm (IQR 16–28), p = 0.002] and lower median stone volume [1624 mm³ (IQR 471–3452) vs. 6123 mm³ (IQR 2987–12456), p < 0.001]. ROC analysis showed optimal cutoffs of 19 mm for size (AUC 0.788, 95% CI 0.706–0.871) and 2357.55 mm³ for volume (AUC 0.782, 95% CI 0.699–0.865), with no significant difference between curves (DeLong’s test p = 0.812). Multivariable logistic regression confirmed stone volume as an independent predictor (OR 0.9997 per mm³, 95% CI 0.9995–0.9999, p = 0.002), while stone size was not (p = 0.128). Complication rates were low (fever 4.1%, sepsis 0.8%). Conclusion: Three-dimensional stone volume and maximal diameter demonstrated comparable overall predictive performance for RIRS success. However, stone volume provided independent prognostic value and higher sensitivity at the optimal cutoff (≈2358 mm³), supporting its use for improved preoperative planning and risk stratification.