Re: Factors Predicting Outcomes of Micropercutaneous Nephrolithotomy: Results from a Large Single-Centre Experience

Abstract

The recently developed micropercutaneous nephrolithotomy (microperc) is the miniaturized version of mini-percutaneous nephrolithotomy (PCNL) and standard-PCNL that allows for safe access and stone disintegration under direct vision. In this single-centre study, the authors aimed to define the role of microperc in the management of renal calculi and analyse factors predicting outcomes. A total of 139 patients, who underwent microperc between June 2010 and November 2014, were enrolled in this study. Microperc was successful in 119 (91.53%) patients, while in 11 patients (8.46%) some residual fragments were seen on imaging. Of the total study group, conversion to mini- or standard PCNL was required in nine patients (6.47%). Overall complication rate of 11.53%, primarily minor complications comprising renal colic and urinary tract infection. On multivariate analysis, stone density (HU), stone number and stone volume were significantly associated with the dependent variable stone clearance. Multivariate analysis showed that intra-operative complications and stone number were significantly associated with conversion to mini- or standard PCNL. Stone volume threshold of 1.000 mm3 was a significant predictor of stone clearance in univariate and multivariate analyses, regardless of the stone location. Some limitations of this study, relatively small sample size and particularly the retrospective and non-comparative design, should be highlighted. EAU guidelines recommend shockwave lithotripsy (SWL) or retrograde intrarenal surgery as the primary treatment modality for stones <10 mm in size. Although microperc is presently being used for small to moderate stones, the very indication that holds for SWL as well, it is notable that SWL is influenced by stone location and pelvicalyceal anatomy, and may require multiple sessions. Nevertheless, microperc has an inherent limitation in that the stone fragments cannot be retrieved for analysis. It has been noted that the closed system leads to a pressure rise, especially in scenarios of impacted pelvic stones and longer operating times. This problem may be even more serious in pediatric patients.