The treatment of lower pole stones (LPS) is the field of great controversy in the literature. Each one of the available treatment options has its own advantages and disadvantages especially for stones 20 mm or less . EAU guidelines propose shock wave lithotripsy (SWL), flexible ureteroscopy (fURS) or percutaneous nephrolithotomy (PNL) for the management of lower calyceal stone, setting in the same time some prerequisites regarding the existence of favorable or not anatomy .
It is more than well established in our everyday clinical practice that PNL is the gold standard procedure for large and complex renal stones despite increased complication rates compared with its rivalries (fURS and SWL). No consensus exits though, for the ideal procedure for stones in the ‘gray zone’, such as stones between 1 and 2 cm. Things are getting even more complex because of stone position in the renal calyceal system especially when stones are situated in the lower calyx.
The answer to the aforementioned difficult question has been the field of interest for several contemporary studies. In one of them, a randomized control trial, including nearly 600 patients, a trend towards the superiority of PNL compared with fURS was demonstrated in terms of, stone-free rate (SFR) 87.3% for PNL vs. 82.1% for fURS, need for retreatment 4 vs. 9% and need for auxiliary procedures 12 vs. 18% without these results succeeding in reaching statistical significance. Complication rates were slightly increased but not statistically significant for the PNL group compared with fURS . On the same pace, the results of the most recent meta-analysis confirm the superiority of PNL for lower pole stones 2 cm or less, reporting a SFR 91.3% for PNL vs. 68.5% for fURS (risk ratio 1.32 P < 0.01 and I2 = 57). Despite the fact that there was no sub-group analysis for stones less than 2 cm and greater than 2 cm, the authors conclude that PNL is the most efficient method for treating stones with size between 1 and 2 cm .
Increased invasiveness of PNL compared with fURS led to the development of miniaturized instruments and to a breakthrough in the way this procedure was performed. After the first optimistic results, comparison with the least invasive fURS was inevitable. In one of these comparative studies, ultra-mini PNL (UML) was found to be the most efficient with SFR 98 vs. 92% (P < 0.05) whereas the fURS produces favorable complication rates (6.67 vs. 16.67%) while reaching statistical significance only for the grade I and grade II complications . Kandemir et al.  in their prospective randomized trial, reported high efficacy for both the procedures but failed to prove any difference in terms of complication rates between micro-PNL and fURS. On the other hand, one of the most well designed, multicenter, RCT, has recently published its results. In this study, 160 patients with lower pole stones of 1–2 cm size were enrolled and divided into two groups [super-mini-PNL (SMP) and fURS]. Statistical analysis revealed a robust superiority of PNL procedure with SFR 93.8% for the SMP vs. 82.5% for fURS (P = 0.028) and lower auxiliary rate in the SMP group. In the interesting comparison of the two procedures, complication rates were found to be of no difference . As the above-mentioned results are contradictory, Gao et al. performed a meta-analysis in order to clarify if miniaturized PNL is advantageous over fURS in the setting of lower pole stones. After the statistical analysis, mini-PNL was found to perform better in terms of SFR compared with fURS without any increase in the complication rates that were found to be similar between the two approaches .
Finally, under our point of view, there are some technical and cost limitations to the fURS procedure that do not exist in PNL. Lower calyx is a difficult anatomic part to reach, and despite the fact that an experienced surgeon can surpass this problem, it may be a difficult task for a surgeon in their learning curve. This task may be practically impossible in the setting of unfavorable anatomy (infundibulum length and width may affect ureteroscope movement significantly). In addition, stone density and multiple stones even of size 1.5 cm maybe negative factors for the success of fURS procedure. Finally, because of ureteroscope maximum torsion, the possibility of scope or laser fiber damage is increased, which directly reflects in increased cost. All these thoughts seem to be reinforced by the existing literature [8,9].
Probably, there is no straight answer regarding the optimal procedure for the management of LP stones of 1.5 cm. On the basis of the literature, PNL seems to have higher SFR and lower auxiliary procedures rate but with the cost of slightly increased complication rates. Other factors like cost, surgeons experience and patient's decision and availability of the equipment may influence the final decision. New technologies in the form of miniaturized instruments have decreased PNL disadvantages but the same apply for fURS. Maybe the answer lies to the individualization of each procedure. Nevertheless, one is sure, the procedure that will manage to combine minimal invasiveness with minimal complications will prevail, and in our point of view, PNL is much closer in succeeding this goal.
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