Impact of Lower Pole Calculi in Patients Undergoing Retrograde Intrarenal Surgery

Objective: To assess if the presence of a lower pole stone (LPS) decreases the stone-free (SF) rate following retrograde intrarenal surgery (RIRS). The second purpose was to assess the result of RIRS for LPS and to identify predictors of SF status. Patients and Methods: We retrospectively analyzed 205 procedures in 162 patients with renal stones treated by RIRS between January 2010 and January 2013 at a single institute. The SF status was defined as no residual fragments. Independent-sample t-tests and Chi-square tests were used for comparisons of means and proportions, respectively, between patients with or without LPS. Logistic regression models were used to assess prognostic factors influencing SF status in cases of LPS. Results: LPS were present in 89 (54.9%) patients. There were no differences between patients with or without LPS regarding the mean operative time (p=0.77), the surgeon's experience (p=0.522), the length of hospital stay (p=0.269), and the SF rate (p=0.224). SF status after RIRS in patients with or without LPS was 74.1% and 78% (p=0.224), respectively. In the case of LPS, the presence of multiple stones and a history of percutaneous nephrolithotomy (PCNL) were predictive factors for occurrence of residual fragments in univariate analysis (p=0.037 and p=0.015). In multivariable analysis, only the presence of multiple stones remained as a predictive factor (p=0.027; HR=3.2), whereas a trend was observed when there was a history of PCNL (p=0.07; HR=3). Conclusion: The presence of a LPS does not alter the SF rate of RIRS even in cases of early experience. RIRS for LPS appears to be an effective technique, but special attention should be given to patients with multiple stones and/or a history of PCNL.