External validation of Resorlu-Unsal stone score in predicting outcomes after retrograde intrarenal surgery. Experience from a single institution

Objective: Pre-operative assessment of renalstones is essential in selecting treatmentoptions and achieving high success rates for retrogradeintrarenal surgery (RIRS). Several nephrolithometric scoringsystems have been developed using pre-operative clinical dataand stone characteristics. Resorlu-Unsal stone score (RUSS) iscomposed of four different parameters, and each of them adds 1point to the final score. One point is added in patients with stonesize > 20 mm, lower calyceal stones and infundibulo-pelvicangle < 45°, stone number > 1, and abnormal anatomy, respec-tively. RUSS categorizes patients into four distinct groups andaims to predict stone-free rates (SFR) after RIRS. We externallyvalidated RUSS and evaluated its predictive accuracy.Materials and Methods: We performed a retrospective analysisof patients who underwent RIRS for renal stones betweenJanuary 2020 and December 2021. Patient age, pre-operativehydronephrosis, stone size, stone density as Hounsfield Unit(HU), operative time and RUSS were investigated as potentialpreoperative predictive factors for stone-free status. RUSS wasapplied to all patients, and the nomogram was externally vali-dated. Area under the curve (AUC) was used for clinical validityassessment.Results: The present study included a total of 79 patients. Meanpatient age was 55.1 ± 15.4 years with a mean stone size was14.2 ± 4.4 mm. Overall, 62/79 (78.4%) patients were stone freeafter the initial treatment. After applying RUSS, 36 (45.6%), 29(36.7%), 10 (12.6%), and 4 (5.1%) patients had a score of 0, 1,2, and 3, respectively. On multivariate logistic regression RUSS(OR = 0.220; 95%CI: 0.086-0.567; p = 0.002) was identified asthe only predictor of postoperative stone-free status.Conclusions: RUSS is a user-friendly scoring system that maypredict postoperative stone-free rate after RIRS with great effi-cacy and accuracy