Endourology and Stones Minimally Invasive Percutaneous Nephrolithotomy: A Comparative Study of the Management of Small and Large Renal Stones Mohamed F. Abdelhafez, Bastian Amend, Jens Bedke, Stephan Kruck, Udo Nagele, Arnulf Stenzl, and David Schilling OBJECTIVE To compare the safety and efficacy of minimally invasive percutaneous nephrolitholapaxy (MIP) between small (<2 cm) and large (>2 cm) renal calculi, because although MIP has proved its efficacy in small lower caliceal stones, the efficacy in large renal calculi has been questioned. MATERIALS AND METHODS The data from 191 consecutive minimally invasive percutaneous nephrolithotomy (MIP) procedures at a single institution from January 2007 to March 2011 were reviewed retrospectively. All stone sizes and complexity were included (98 were <2 cm and 93 were 2 cm). We per- formed a comparative analysis of procedures for calculi <2 cm and 2 cm regarding the stone-free rate, the need for auxiliary procedures, and complications. The Student t test for parametric continuous variables and the chi-square test or Fischer’s exact test for nominal variables were applied. RESULTS The primary stone-free rate was significantly lower for the large than for the small stones (76.3% vs 90.8%, P ¼ .007), and the secondary stone-free rate after one auxiliary procedure (second-look percutaneous nephrolithotomy, ureterorenoscopy, or shock wave lithotripsy) was not significantly different between the 2 groups (94.6% vs 98.9%, P ¼ .1). The total complication rate was not significantly different (26.9% vs 19.4%, P ¼ .2) between the 2 groups either. Grade III complications occurred in 5.2% of all patients, and no grade IV or V complications were observed. CONCLUSION Using MIP, the total stone-free rate was greater for the small than for the large calculi; however, most patients could be rendered stone-free with the use of one auxiliary procedure. The high success rate and low rate of higher grade complications justify the application of MIP for large stones. UROLOGY 81: 241e245, 2013. Ó 2013 Elsevier Inc. M iniaturized percutaneous nephrolitholapaxy (minimally invasive percutaneous neph- rolithotomy [PCNL]) was initially described as an alternative percutaneous approach to large renal stones in a pediatric patient population. 1 Compared with the large-bore conventional PCNL system with a diam- eter of 28F-32F, the original miniaturized system had a diameter of 11F. Currently, no clear-cut definition is available for mini-PCNL; however, in recent studies, most investigators have referred to instruments with an access diameter of 15F-22F. During the past 5 years, mini- PCNL has gained increasing popularity and is now widely used to overcome the therapeutic gap between conven- tional PCNL and less-invasive procedures such as shock wave lithotripsy (SWL) or flexible ureterorenoscopy (URS) for the treatment of lower pole calculi or larger residual fragments. 2-4 Although several studies have shown the safety and efficacy of mini-PCNL for small calculi, the fear of reduced visibility, a prolonged oper- ating time, and lower primary stone-free rates owing to the reduced shaft diameter has resulted in reluctance to apply miniaturized instruments in patients with a larger stone burden. 5,6 In 2005, the technique of minimally invasive PCNL (MIP) was developed and has completely replaced conventional PCNL at our department. MIP is characterized by the use of a 12F nephroscope and an 18F access sheath and continuous low-pressure irrigation, allowing for accelerated stone retrieval without the need for additional stone graspers or baskets and immediate closure of the access tract without the need for neph- rostomy placement. 5-7 It has shown high efficacy and safety in the management of small, lower caliceal stones, Financial Disclosure: The authors declare that they have no relevant financial interests. From the Department of Urology, Eberhard-Karls-Universität Tübingen, Germany; Department of Urology, Assiut University Hospital, Assiut University, Assiut, Egypt; and Department of Urology and Andrology, Landeskrankenhaus Hall in Tirol, Tirol, Austria Reprint requests: David Schilling, M.D., Department of Urology, University of Tuebingen, Hoppe-Seyler-Strasse 3, Tuebingen 72076, Germany. E-mail: david. schilling@kgu.de Submitted: August 3, 2012, accepted (with revisions): September 19, 2012 ª 2013 Elsevier Inc. 0090-4295/12/$36.00 241 All Rights Reserved http://dx.doi.org/10.1016/j.urology.2012.09.030