Seoul National University Renal Stone Complexity Score for Predicting Stone-Free Rate after Percutaneous Nephrolithotomy

Abstract

Objectives: Currently, no standardized method is available to predict success rate after percutaneous nephrolithotomy. We devised and validated the Seoul National University Renal Stone Complexity (S-ReSC) scoring system for predicting the stone-free rate after single-tract percutaneous nephrolithotomy (sPCNL).

Patients and methods: The data of 155 consecutive patients who underwent sPCNL were retrospectively analyzed. Preoperative computed tomography images were reviewed. The S-ReSC score was assigned from 1 to 9 based on the number of sites involved in the renal pelvis (#1), superior and inferior major calyceal groups (#2-3), and anterior and posterior minor calyceal groups of the superior (#4-5), middle (#6-7), and inferior calyx (#8-9). The inter- and intra-observer agreements were accessed using the weighted kappa (κ). The stone-free rate and complication rate were evaluated according to the S-ReSC score. The predictive accuracy of the S-ReSC score was assessed using the area under the receiver operating characteristic curve (AUC).

Results: The overall SFR was 72.3%. The mean S-ReSC score was 3.15±2.1. The weighted kappas for the inter- and intra-observer agreements were 0.832 and 0.982, respectively. The SFRs in low (1 and 2), medium (3 and 4), and high (5 or higher) S-ReSC scores were 96.0%, 69.0%, and 28.9%, respectively (p<0.001). The predictive accuracy was very high (AUC 0.860). After adjusting for other variables, the S-ReSC score was still a significant predictor of the SFR by multiple logistic regression. The complication rates were increased to low (18.7%), medium (28.6%), and high (34.2%) (p = 0.166).

Conclusions: The S-ReSC scoring system is easy to use and reproducible. This score accurately predicts the stone-free rate after sPCNL. Furthermore, this score represents the complexity of surgery.

Figure 1. Schematic representation of the Seoul National University Renal Stone Complexity (S-ReSC) scoring system.

The score is calculated by counting the number of sites involved, regardless of the size and number of the stones. (a) The sites were as follows; the renal pelvis (#1), the superior and inferior major calyceal groups (major calyx and infundibulum) (#2–3), and the anterior and posterior minor calyceal groups of the superior (#4–5), middle (#6–7), and inferior calyx (#8–9). (b) The anterior and posterior division was simply divided using the frontal plane of the kidney. Example of computed tomography axial (c) and coronal (d) images of the renal stone with S-ReSC score 4. The renal stone involved the renal pelvis (#1), superior major calyceal group (#2), and the anterior and posterior minor calyceal groups of the superior calyx (#4 and #5).

Figure 2. A calibration plot of the Seoul National University Renal Stone Complexity (S-ReSC) score to predict the stone-free rate after single-tract percutaneous nephrolithotomy.

Figure 3. Decision curve analysis.

The curve demonstrates a positive net benefit in almost all threshold probabilities using the Seoul National University Renal Stone Complexity (S-ReSC) score to predict the stone-free rate after single-tract percutaneous nephrolithotomy.