The LC stones have always been problematic in order to obtain a total stone clearance. It is very well discussed in literature as a systematic review and meta-analysis showed PCNL and RIRS were superior to ESWL in stone clearance and even PCNL is more effective then RIRS(9). In 2017 Bozzini et al. performed a prospective randomized comparison among ESWL, PCNL and RIRS on <2cm sized LC stones(10). ESWL was failed against PCNL and RIRS considering SFR and re-treatment rates(p<0.05). The SFRs were significantly higher in PCNL(87.3%) and RIRS(82.1%) as compared to ESWL(61.8%). The duration of procedure and hospital stay, radiation exposure favored RIRS against PCNL(10). RIRS looks a feasible and better option against PCNL when complication rates were also taken in consideration. But still RIRS may not be performed on all LC stones successfully due to anatomic variations as narrow ureter or calyceal infindibulum. So among with the miniaturized PCNL modalities as MP, UMP and MicroPNL there need of a decision to choice the priority for most effective and safe intervention against <2cm LC stones even in case of narrow calyx existence(2).
The MP was first described and experienced with a single step dilatation with usage of 11 Fr sheath on 11 cases at preschool age(11). At the same year an initial results from an adult study appeared(12). Nine patients with <2cm stones were treated with 13 Fr MP. 89% stone-free rate was achieved while with better outcomes in selected patients favoring MP for blood loss, hospital stay and postoperative pain(12). Despite this, Giusti et al. declared that MP had no obvious advantage against PCNL and concluded as tubeless PCNL could be a better option(13). But Knoll et al. defended that not all tubeless PCNL procedures has ended with delighted results. Some cases need auxiliary interventions. Even being a limitation in their study that stone sizes were smaller in MP patients; the results were comparable in means of safety and effectiveness. More, the short hospital stay, less pain and more possibility for tubeless completion of operations has favored MP(14). The MP studies have showed comparable and equal SFR and reduced comorbidities compared to conventional PCNL(8, 14, 15). ElSheemy et al. compared MP and standard PCNL through 18 and 30 Fr tracts respectively(16). According to their results there was significant difference on SFR in between patients who had larger stone burden (>2cm2). But for those with singular stones or stone burden ≤2 cm2; there was no significant difference in SFR and also MP showed lower complications compared to standard PCNL(16). Similar to the current literature, in our study there was no significant difference in between SFR of PCNL and MP(p=0.33) while a significant difference in between complication rates (p=0.001)(Table 2).
In 2013, the UMP technique was published with initial experiences in literature (17). Desai et al. used a 6 Fr mini nephroscope through a 11/13 Fr metal sheath on 36 consecutive patients with stone size of <2cm(17). Similar to our access method, ultrasonographic guidance was also used in addition to fluoroscopy. Not all stones were located in LC. The LC stone ratio and LC access ratio were 27.8% and 38.9% respectively while 8.3% of their patients had multiple calyceal stones. Their immediate (postoperative 1st day) and total (postoperative 1st month) SFR’s were 88.9% and 97.2% respectively(17). More, their significant complication (urosepsis, extravasation and fever) ratio was 16.7% and need for a second intervention was 2.8% whereas ours were 2.4% and 12.1% respectively. This inverse ratio may be explained with the differences between operative time, stone analysis, surgeon experience or other patient characteristics in between the studies.
In a cohort study of 98 consecutive UMP patients, the mean stone size was 15.85±4.53mm which was comparable of ours (15.23±3.3mm) but their postoperative SFR on 1st month control was 83%(18). Jones et al. published a systematic review study investigating the role of MicroPNL and UMP. Across seven studies a total of 262 patients were undergone UMP with a mean of stone size 18.6mm, SFR of 88.3% and complication rate of 6.2%(19). In our study, we calculated the SFR on 3rd month control. The SFR of our UMP was calculated as 78% which was also significantly lower than our PCNL and MP groups.
Ganpula et al. discussed well the differences between PCNL , MP and UMP(7). The cross-sectional area and length differences of access sheats and more the smaller fragments obtained during MP all create a superior fragment vacuum clearance during MP compared to PCNL. Also sheath sizes of MP may give a chance to use flexible nephroscope for stone fragments in smaller different calyces(7). So these all may participate to the similar SFR in between PCNL and MP. Again in another study, during the interventions on 15-30 mm renal stones, 16.5 Fr MP showed comparable SFR but lower complications as compared with 24 Fr PCNL(20). According to a recent review study the terminology seems to be confusing in between the modalities but all miniaturized tract size interventions result with better outcomes in terms of pain and complication rates whereas comparable SFR with standart PCNL(21). Depending on our comparison in between MP and UMP complication ratios were comparable but our SFR results in between MP and UMP were statistically significant(p=0.02). According to our results mean stone size were similar as 16.38 mm, 17.82 mm and 15.23 mm respectively. The UMP looks like an alternative to MP but may not be satisfactory especially for interventions on stones with >1.5 cm sized. The UMP may also be a good alternative to RIRS especially for medium sized (<1.5 cm) LC stones. This mismatch between the ideal indication for UMP and the stone size treated with UMP in this study may have meaningful bias on the results and downgraded the potential efficacy of UMP. However, currently due to the lack of literature there are no clear guideline on MP and UMP.
The PCNL was at highest risk of complication co-existence. The clinically evident complications in Table 3a were all higher in PCNL compared to MP and UMP. Only among those, between PCNL and MP the severe pain seems to be questionable(p=0.05). According to Mishra et al. the need of postoperative analgesics were similar between PCNL and MP(8). More in contrast to PCNL, none of the patients who were undergone MP and UMP procedures needed a further surgical or endoscopic interventions according to Clavien-Dindo classification(22) score of >III(Table 3b). Also there was no difference among clinically evident complications between MP and UMP. Careful selection of patients, experience of surgeon and special equipment for each intervention is essential.
The number of the patients in each groups may be a statistical limitation. So we can assume that surely the tendency (obtained by univariate analysis) would be better confirmed by randomized control trial with higher numbers on which we are already working.
Here in our study a limitation may be lack of evaluation according to the stone analysis or Hounsfield unit (HU). We did not include pediatric age group (<18) in order not to increase the heterogeneity with extra choice of MP and UMP. Moreover, exclusion of patients more than 75 years old seems to be a potential selection bias but but increased risks with older age under general anesthesia may require incomplete termination of procedure which may also be a cause of bias on postoperative outcomes.
Tubeless or non-tubeless comparison may be also considered in future studies. MP may seem to be supported as first choice of PCNL subtype considering the 1-2 cm sized LC stones. UMP may be recommended for certain selected patients. Further studies with giant patient groups may show comparable SFR in between MP and UMP. As last, the use of the same Holmium laser energy during the interventions might give the possibility to focus only on the technique chosen and not a different kind of energy to break the stone.