Evaluation of Nephrolithometric Scoring Systems to Predict Outcomes of Retrograde Intrarenal Surgery

The aim of the study was to evaluate the predictive value of nephrolithometric scoring systems used to predict the complexity of renal stones for the outcomes of retrograde intrarenal surgery (RIRS).

A total of 81 patients who underwent RIRS for nephrolithiasis between January 2013 and October 2017 were reviewed in this retrospective study. Guy's Stone Score (GSS), the S.T.O.N.E., Clinical Research Office of the Endourologic Society (CROES), and Seoul National University Renal Stone Complexity (S-ReSC) nephrolithometry scores were assessed by same researcher for each patient from preoperative non-contrast enhanced computed tomography scans. These nephrolithometric scores, stone characteristics and complications were compared in patients with/without residual stone.

The median (IQR) age of patients (37 female/44 male) was 45 (20) years. The median (IQR) stone burden was 139.4 (125.4) mm2 and the mean Hounsfield unit (HU) value was 1034.46 ± 239.56. The stone burden, S.T.O.N.E. and S-ReSC scores were statistically significantly higher and the CROES score was significantly lower in patients with a residual stone (p < 0.001, for all). The incidence of residual stones was statistically significantly higher in patients with Grade 3 GSS (p = 0.018). While S.T.O.N.E., S-ReSC and CROES were significantly correlated with stone-free rates, GSS failed to correlate with stone-free status. According to the receiver operating characteristic (ROC) curve analysis, the predictive value of stone burden was higher for residual stones, compared to S-ReSC scoring (p < 0.05).

Nephrolithometric scoring systems nomograms used to predict the PCNL success were not superior to stone burden in predicting the RIRS success.