To predict the outcome of flexible ureteroscopy in the management of renal stones based on preoperative scoring module using five preoperative parameters that have effect on stone free status postoperatively.

Although flexible ureteroscopy has been in use for decades, neither the European Association of Urology (EAU) nor the American Urological association (AUA), in their clinical guidelines, recommends flexible ureteroscopy (FURS) as a first-line procedural treatment for renal stones . Several reports showed that FURS is a suitable alternative to shockwave lithotripsy (SWL) and percutaneous nephrolithotripsy (PCNL) for the treatment of renal stones, with potentially higher stone-free rates than SWL and lower morbidity than PCNL.

Safe and effective removal by FURS of multiple and large intrarenal stones, including lower pole calculi, has been documented suggesting that FURS is effective for complex intrarenal stone removal . With the multitude of available procedures, selection of the optimal one for management of renal stone is becoming more challenging.

Established models for predicting the outcomes of SWL and PCNL exist . However, a predictive model for predicting the outcome of URS is still in development , particularly for FURS treatment of renal stones. Four scores have been developed for FURS. Two of these have been compared and validated in different cohorts: the Resolu Unsal Stone Score (RUSS) and modified Seoul National University Renal Stone Complexity (S-ReSC) score , the other two scores, the S.T.O.N.E score described by Molina et al. and Ito's nomogram.

Many studies have demonstrated that stone volume is the most significant factor predictive of stone-free status (SF) after FURS. The investigators speculate that stone volume combined with other variables might improve prediction of SF after FURS. The aim of the present study is to evaluate various preoperative parameters as predictors of FURS outcome based on the Ito's nomogram

Inclusion Criteria:

1. Renal stones (≤ 2 cm)
2. Radiolucent stone resistant to SWL and oral chemical dissolution treatment (≤2cm)

Exclusion Criteria:

1. Large stones (> 2 cm).
2. Staghorn stone (stone involving the renal pelvis and more than two calyces).
3. Patient preference of other treatment modality

Patients with renal stones that are < 2 cm in maximal diameter will be recruited to the study. Patients will be counseled for flexible ureteroscopy, and the procedure will be explained to them with discussion about its pros and cons. Patients agreeable to enrollment will sign an informed written consent after fulfillment of ethical approval forms.Stone free rate will be assessed at one week, one month, and three months post-operatively using Plain X-ray for radio-opaque stones and NCCT for radiolucent stones.

Stone free rate will be determined by no stone fragment > 4mm. Number of ancillary procedures required to reach SF will be reported