In our study, although ureteral stent encrustation was related to the indwelling time, heavily encrusted ureteral stents necessitating additional procedures for removal occurred within an indwelling time of 3 months. The exact interval for removal of an indwelling ureteral stent to avoid additional procedures for removal is therefore difficult to determine.

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ObjectiveTo develop and internally validate a preoperative nomogram for predicting stone-free status (SF) after flexible ureteroscopy (fURS) for renal stones, as there is a need to predict the outcome of fURS for the treatment of renal stone disease. Patients and MethodsWe retrospectively analysed 310 fURS procedures for renal stone removal performed between December 2009 and April 2013. Final outcome of fURS was determined by computed tomography 3 months after the last fURS session. Assessed preoperative factors included stone volume and number, age, sex, presence of hydronephrosis and lower pole calculi, and ureteric stent placement. Multivariate logistic regression analysis with backward selection was used to model the relationship between preoperative factors and SF after fURS. Bootstrapping was used to internally validate the nomogram. ResultsFive independent predictors of SF after fURS were identified: stone volume (P < 0.001), presence of lower pole calculi (P = 0.001), operator with experience of >50 fURS (P = 0.026), stone number (P = 0.075), and presence of hydronephrosis (P = 0.047). We developed a nomogram to predict SF after fURS using these five preoperative characteristics. Total nomogram score (maximum 25) was derived from summing individual scores of each predictive variable; a high total score was predictive of successful fURS outcome, whereas a low total score was predictive of unsuccessful outcome. The area under the receiver operating characteristics for nomogram predictions was 0.87. ConclusionThe nomogram can be used to reliably predict SF based on patient characteristics after fURS treatment of renal stone disease.

Abbreviations & AcronymsAbstract: A large renal stone can be treated ureteroscopically, but the treatment often requires more than one procedure. The use of stenting before ureteroscopy was recently reported. The present study investigated the effectiveness of preoperative stenting before ureteroscopic lithotripsy for large (>15 mm) renal stones. A ureteral stent was intentionally inserted in 25 patients undergoing ureteroscopic surgery. A group of 36 non-prestented patients was used as control. Median stone diameter was 21 mm in both groups. Pre-ureteroscopy stenting significantly improved the stone-free rate, defined as stones <2 mm and <4 mm (P < 0.05), whereas it did not significantly improve the stone-free rate defined as 0 mm (P = 0.12). The uretereoscopy success rate was 72.0% in the stented and 55.6% in the control group (P = 0.09). A 14/16-Fr ureteral access sheath was successfully inserted in 94.7% of the stented patients, and 74.2% of the non-stented patients (P < 0.05). Our findings showed that preoperative stenting is effective for dilation of the ureter, and also to facilitate the insertion of a ureteral access sheath in patients undergoing ureteroscopic lithotripsy for large renal stones.

We found that both the maximum and average attenuation coefficients on NCCT are significantly related to the fragmentation efficiency. In addition, this study showed that, in patient groups with stone a burden <20.0 mm in diameter, both the maximum and average attenuation coefficients were significantly predictive of operative time.