Predictors of Persistent Residual Stones After Second Look Percutaneous Nephrolithotomy.

Abstract

Introduction: Second look flexible nephroscopy (SLFN) is often offered after percutaneous nephrolithotomy (PCNL). However, even after SLFN, residual fragments (RFs) occasionally persist. We sought to determine the incidence of persistent RFs in patients who undergo SLFN for RFs after PCNL and to identify parameters predictive of persistent RFs. Methods: We identified all patients at our institution with RFs on post-PCNL computed tomography (CT) that underwent SLFN between 1/2016 and 5/2020. Patient demographics, stone characteristics, and perioperative parameters were analyzed for each study patient. Post-SLFN fragments were identified on either follow-up kidney, ureter, and bladder radiograph or CT imaging obtained within 3 months of PCNL. Multivariable logistic regression analyses (MVA) was performed to identify predictors of persistent fragments. Results: A total of 201 renal units met the inclusion criteria. The median size of the largest RF at the time of SLFN was 5 mm (IQR 2-8) and the median cumulative RF stone size was 8 mm (IQR 5-14). The final stone-free rate of patients with RFs on initial PCNL who then underwent SLFN was 60.7% (n = 122). The median cumulative RF stone size and the median size of the largest RF post SLFN was 6.5 mm (IQR 4-12) and 5 mm (IQR 3-8), respectively. On MVA, bilateral preoperative stones and greater RF stone burden at time of SLFN were independent predictors of radiographically detected post-SLFN fragments. Conclusions: Among patients who underwent SLFN for RFs after PCNL, 60% were rendered stone-free. Patients with bilateral stones prior to PCNL and greater RF stone burden at time of SLFN are more likely to have persistent fragments, despite attempts at aggressive stone removal during both the initial PCNL and subsequent SLFN. The risk of adverse stone events from such fragments is unknown and may be lower because of their inaccessibility.