Letter to the Editor
Super-mini percutaneous nephrolithotomy (SMP) versus retrograde intrarenal surgery for the treatment of 1-2 cm lower-pole renal calculi: an international multicenter randomized controlled trial
We are interested to read the study by Zeng et al.  and appreciate the authors for their study showing that super-mini-percutaneous nephrolithotomy (SMP) was more effective than retrograde intrarenal surgery (RIRS) to treat 1-2 cm lower-pole renal calculi in terms of a better stone-free rate and lesser auxiliary rate. However, some issues still require clarification in this study.
The study validated that SMP was more effective than RIRS to treat 1-2 cm lower-pole renal calculi. However, the results should be explained with caution. As we known, pyelocaliceal anatomy seriously influences the performances of flexible ureteroscopy, while no obvious affection for SMP . This parameter should be evaluated before patients were randomized into RIRS groups. Although there were no significant differences in characteristics of lower-pole spatial anatomical between the two groups, it would be more reasonable and reliable to compare the efficacy between SMP and RIRS, after excluding the patients with unfavorable pyelocaliceal anatomy such as an acute infundibulopelvic angle, or a long lower-pole calyx infundibulum.
The authors set a definition of stone-free status as no residual fragments of ≥0.3 cm on KUB and ultrasound at 1-day and on CT scan at 3-months after operation. We are curious to know how the authors managed when the results were different between KUB and ultrasound. As the primary endpoint was the stone-free rate at 3-months after surgery, we would like to know the size of the residual fragments in the 6.2% (5/80) of patients in SMP and 17.5% (14/80) in RIRS. Do they need another auxiliary procedure? All those information is important for drawing the final conclusion.
The study was an international multicentre, prospective, randomized, non-blinded controlled study, conducted at 10 academic medical centers in China, India, and Turkey. The authors said the two groups had similar baseline characteristics, but we would like to know if it was so for each center. If not, did it affect the final results when exclude those centers?
In conclusion, Zeng et al. made a laudable effort and have provided a level-1 evidence comparing the two modalities for treating 1-2 cm lower-pole renal calculi, but the authors’ conclusion should be taken with caution until more reasonable prospective studies with large sample size have been conducted. We look forward to the authors’ reply to clarify our queries.
Conflict of interest
The authors declare that they have no conflicts of interests.
Huiming Jiang1*, Nanhui Chen1
1Department of Urology, Meizhou People’s Hospital (Huangtang Hospital), Meizhou Hospital Affiliated to Sun Yat-sen University, No.63, Huang Tang Road, Meizhou 514031, Guangdong, People’s Republic of China.
- Zeng G, Zhang T, Agrawal M et al. (2018) Super-mini percutaneous nephrolithotomy (SMP) vs retrograde intrarenal surgery for the treatment of 1-2 cm lower-pole renal calculi: an international multicentre randomised controlled trial. BJU international. 2018;122(6):1034-1040. doi: 10.1111/bju.14427
- Geavlete P, Multescu R, Geavlete B (2008) Influence of pyelocaliceal anatomy on the success of flexible ureteroscopic approach. Journal of endourology 22 (10):2235-2239. doi:10.1089/end.2008.9719