Which factors affect the spontaneous stone passage after flexible ureteroscopic lithotripsy for renal stones?

Abstract Objectives: The aim of this study was to investigate factors predicting spontaneous stone passage after flexible ureteroscopic lithotripsy ( fURS) for renal stones. Materials and Methods: This study included 239 patients with renal stones who underwent fURS using the dusting technique. The final outcome was evaluated 3 months postoperatively and the residual fragment status (RFs) was defined as any residual stone fragments greater than 2 mm. Univariate and multivariate analyses of possible predictive factors associated with spontaneous clearance of residual renal fragments were performed. Results:186 patients(77.8%) had achieved an stone-free status (SFs) and 53 patients(22.2%) were considered with RFs. Univariate analysis showed the stone location, stone number, stone size, stone CT value, IPA degree, the presence of hydronephrosis and stone covered with purulent substance were all associated with RFs (P<0.05). Multivariate logistic regression analysis showed that larger stone size (P=0.001),multiple stones (P=0.038) , the IPA of <45°(P=0.035) , the presence of hydronephrosis (P=0.045), the stone CT value ≥1000 (P=0.047) were all significantly associated with higher rates of residual stone after fURS. The stone covered with purulent substance was found to be the strongest predictor of RFs (P=0.027). However, the presence of lower pole stone had no significant influence on stone clearance after fURS (P=0.263). Conclusions: Stone number, stone size , an IPA of <45°, stone CT value ≥1000 HU, stone covered with purulent substance and presence of hydronephrosis are all predictive factors of the spontaneous clearance of residual renal fragments after fURS.