Limitations of standard scoring systems in predicting PCNL outcomes for horseshoe kidney patients.

OBJECTIVE: This study aims to evaluate and compare the predictive performance of three widely used nephrolithometry scoring systems—S.T.O.N.E., CROES, and Guy’s Stone Score—in determining stone-free outcomes following percutaneous nephrolithotomy (PCNL) in patients with horseshoe kidney (HSK), a population in which the utility of these models remains uncertain. METHODS: In this retrospective single-center study, 64 adult patients with HSK who underwent unilateral PCNL between January 2017 and December 2024 were included. Preoperative non-contrast CT images were used to assess S.T.O.N.E., CROES, and Guy’s scores by two blinded endourologists. The primary outcome was stone-free rate (SFR), defined as complete clearance or residual fragments < 4 mm at 1-month postoperative CT. Predictive performance was evaluated via univariate/multivariate logistic regression and ROC curve analysis. RESULTS: The overall SFR was 65.6%. All three scoring systems were significantly associated with SFR in univariate analysis. However, in multivariate analysis, only the CROES score remained an independent predictor of SFR (OR: 1.07; 95% CI: 1.02–1.13; p = 0.005). ROC analysis demonstrated the highest predictive accuracy for the CROES score (AUC: 0.81), followed by the S.T.O.N.E. score (AUC: 0.71) and Guy’s score (AUC: 0.55). CONCLUSION: Among the evaluated scoring systems, the CROES nomogram achieved the best predictive performance; however, all three tools were developed for standard renal anatomy and demonstrated limited applicability in horseshoe kidney. These findings highlight the need for scoring models specifically adapted to this population.