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Is mini-percutaneous nephrolithotomy the way to go for renal stones? No!

Knoll, Thomas

doi: 10.1097/MOU.0000000000000614
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Urologische Klinik, Klinikum Sindelfingen-Boeblingen, Sindelfingen, University of Tuebingen, Germany

Correspondence to Thomas Knoll, MD, PhD, MSc, Department of Urology, Klinikum Sindelfingen-Böblingen, Arthur-Gruber-Street 70, 71065 Sindelfingen, Germany. Tel: +49 7031 9812501; fax: + 49 7031 9812342; e-mail: t.knoll@klinikverbund-suedwest.de

Miniaturized percutaneous nephrolithotomy, often called mini-PCNL, was first described as a technique in children, by using a peel-away sheath and an ureteroscope [1]. Others have further developed the technique with specially designed small scopes, following the idea of reduced morbidity by reducing the size of the access tract [2,3]. The available armamentarium reaches from 4.85 F needle scopes to 22 F systems that are not far away from what is called standard or conventional PCNL, usually with outer sheath diameters of 24 F or larger [4–6]. Unfortunately, a marketing-triggered confusing terminology is used, introduced by the inventors using superlatives like ‘super’ or ‘perfect’ or T-shirt sizes like XL, L or S [7]. More precisely, one should rely on the size of outer diameter of the percutaneous sheath, that gives more objective information. It is important to recognize, that miniaturization is not just reducing the diameter. The smaller sizes require several modifications of the technique, including dilatation, lithotripsy or exit strategy. Furthermore, although the hypothesis seems to be convincing, there is no automatism that the procedure becomes less invasive by reducing the tract size. Terms like ‘minimalinvasive nephrolithotomy (MIP)’ are misleading [8], as the concept of percutaneous stone surgery is minimally invasive since its introduction – why it has terminated the age of open stone surgery almost 40 years ago [9]. Many factors impact the outcome of the procedure, as stone characteristics, puncture and dilatation technique, and of course, surgical skills. It is surprising, that many surgeons push mini-PCNL forward as a new standard, though only few studies support such statements [4]. An EAU Systematic Review could recently demonstrate at best a comparable stone-free rate with miniaturized instruments compared with standard (by the cost of longer operative times), but only a tendency of a lower risk of bleeding [10]. Overall study quality was low with high risks of bias and heterogeneous groups. Moreover, miniaturized access included all sizes 18 F or less, including needlescopic access. Beyond this scepticism, chosen instruments and access shall clearly be adapted to the individual patients. Children, difficult anatomy, like diverticular stones or narrow infundibula may need smaller accesses. But does the standard patient benefit from miniaturized PCNL? This answer cannot be given yet, and no guideline gives advice on this. But what can be observed in daily practice is an increasing frequency of PCNLs in medium-sized stones instead of ureteroscopy or extracorporeal shock wave lithotripsy, justified by miniaturization. Caution is advisable considering the very weak available data supporting this concept. It is worldwide accepted, that retrograde ureteroscopy, that competes with mini-PCNL, comes with significantly lower complication risk than percutaneous surgery. Using superlatives for marketing is dishonest to our patients as it raises expectations that might not be fulfilled. Maxi complications may occur even with micro access. Size might matter, but what matters more are the right indication and a skilled surgeon.

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Acknowledgements

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Financial support and sponsorship

None.

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Conflicts of interest

There are no conflicts of interest.

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REFERENCES

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