How Reliable Is the Intraoperative Assessment of Residual Fragments During Percutaneous Nephrolithotomy? A Prospective Study

Objectives: To determine the accuracy of the surgeon's impression as to the stone-free rate at the end of percutaneous nephrolithotomy (PCNL), and to evaluate predictors for inaccurate estimation. Materials and Methods: A prospective study conducted between 2010 and 2015. Surgeon's impression, categorized as insignificant residual fragments (RFs) (<4mm) or significant RF (>4mm), was recorded at the end of PCNL, and was compared with postoperative imaging results, using CT or a combination of US and kidney, ureter, and bladder radiograph for radiolucent and radio-opaque stones, respectively. The association between missed significant RF and the patient and operative variables was evaluated with univariable and multivariable logistic regression analysis. Results: The study cohort included 312 patients. Significant RFs were found in 75 (24%) patients, comprising all 22 patients in whom RFs were suspected (100%) and 53 patients who were considered stone free (18.6%). The sensitivity, specificity, and positive and negative predictive value of the surgeon's estimation for the absence of significant RFs were 100%, 39%, 0.83, and 1 for radiopaque stones, and 100%, 12.5%, 0.75, and 1 for radiolucent stones. On multivariate analysis, multiple stones (OR=4, 95% CI: 1.85-8.7, p<0.001) and cumulative stone size (OR=1.04, 95% CI: 1.02-1.1, p=0.005) were independent predictors for missed RFs. Conclusion: In approximately fifth of the patients undergoing PCNL, the surgeon's impression of insignificant RF may be inaccurate. Stone size and number were independently associated with higher miss rate. These data should be shared with the patients when the postoperative drainage method and the option for an auxiliary procedure are discussed.