Presence of multiple stones with the same overall diameter instead of a single stone wich influence has on stone free rate?

Letterio D'Arrigo1, Francesco Savoca1, Angela Costa1, Astrid Bonaccorsi1, Antonio Cacciola1, Ernst Witt2, Nazia Gill2, Michele Pennisi1
  • 1 Ospedale Cannizzaro, U.O. Urologia (Catania)
  • 2 Statistic and Probability Unit - University of Groningen (Groningen )


Over the last years the high diffusion of endoscopic intrarenal surgery reduced percutaneous treatments. In selected cases it offers to treat patients with stones above 2 cm in diameter.
Some studies have evaluated some paremeters as predictive of stone free rate like stone burden, others the influence of calyx anatomy an its spatial position in particular the infundibular width (IW), infundibular length (IL), and infundubular angle (IPA) on stone free after extracorporeal lithotripsy or RIRS.
In some studies a percent of success > 90% in presence of renal stones treated by RIRS and 85 % in presence of lower pole stones ere reported. However it’s still unclear if calyx anatomy influenced the stone clearance in patients who have undergone to RIRS (8,9).
When multiple stones are present, the retrograde approach is not always shared; the guidelines consider the stones location and size as only elements that affect the choice of treatments.
The objective of our study is to evaluate stone free-rate when multiple stones with the same overall diameter instead of a single stone are present.

Materials and Methods

n the period between June 2012 and December 2013, 106 patients with urinary stones were treated with RIRS. A total of 115 procedures were performed.
Anagraphic data, stone burden and density, number of stones, operative time, kidney anatomic data (infundibular length, collector width, and infundibolopyelic angle), idronephrosis, preoperative presence of nephrostomy tube or double J were evaluated. Stone burden and density stones were analyzed by preoperative NCCT scan.
When more than one stone was present the diameter, volume and area was calculated like the sum of a single value.
All procedures were performed under general anesthesia and a semirigid ureterorenoscope with a 6/7.5F or 8/9.8 was used routinely for dilatation of the ureter passed over a hydrophilic guidewire. After an ureteral access sheath was placed. In all patients a flexible URS, with 200 micron holmium laser lithotripsy was used. We used a holmium-yag laser machine set at an energy level for stone fragmentation or pulverization according to type of urinary stone and choice of setting was entrusted to the operator on the basis of his experience. Basket fragment extraction was not routinely performed but when basketing was deemed necessary, we used a 1.9F zero-tip nitinol stone basket. The operators were two urologists with the same experience having performed more than 50 flexible ureterorenoscopy. A double J stent was placed in every patient after procedure. If the operative time was over 90 min we stopped intervention and placed a double j.
We considered patients without stones or residual fragments below 4 mm after a three months treatment stone free. The software R was used for statistical analysis.
We considered patients without stones or residual fragments below 4 mm after three months of treatment, stone free. The software R was used for statistical analysis.


Statistical analysis showed that the diameter (p=0.0006), and presence of stones in more than one location (p=0.017) correlate significantly with outcome treatment.
The overall stone free rate was 77%; We classified the stone free rate according to diameter ≤ 2 cm and > 2 cm. The SFR were for the stone burden ≤ 2 cm and > 2 cm on diameter were 85% and 55% respectively. Among eighty six records of patients who had stone burden ≤ 2 cm, seventy three (85%) were stone free, therefore our overall stone free rate for the stone burden ≤ 2 cm was (85%). For the stone burden > 2 cm our overall stone-free rate was 55%.
The infundibular length (p=0.186), width (p=0.207), angle (p=0.252), volume (p=0.3573), density (p=0.7784) didn’t correlate to SF.
However, if we considered only patients with stones in lower pole, an infundibolopielic angle below to 38.2° it would negatively influence stone free rate (p=0.001).
Operation time was less in the patients SF (p=0.0003) and a correlation with stone size (p=0.0002) was found.
Stone density has statistically significant correlation with operation time (p=0.01).
When the diameter is the same the presence of more than one stone worsened stone free rate and these results are statistically significant. We can see clearly in the above table 1 that when the diameter and number of stones increases, the probability of stone free patients started to decrease. Anyway the clinical effects of this have a low relevance.

Stone diameter
N° of stones 1 cm 2 cm 3 cm 4 cm
1 94% 81% 55% 25%
2 94% 80% 52% 23%
3 93% 78% 50% 21%
4 92% 76% 47% 20%


Intrarenal retrograde laser lithotripsy and SWL are considered the treatment of choice in patients with renal stones < 1 cm, recommends percutaneous procedures in patients with stones over 2 cm. Anyway in presence of stones between 1 and 2 cm EAU guidelines recommend as treatment to prefer SWL or endourologic procedure without distinction between RIRS o PCNL. In presence of lower pole stone between 1 and 2 cm with non favourable factors to SWL the endourology treatment is recommended as treatment of first choice.
The reasons of these are represented by presence high percentage of residual fragments after SWL who are related to stone size and composition, and to pielocalycal anatomy. Lingeman et al, reported, in a meta-analysis study an overall stone free rate of 59,2% and 90% in patients with lower pole stones of 1-2 cm treated respectively with SWL an PCNL. Another recent prospective, randomized study compare shock wave lithotripsy, retrograde intrarenal surgery and miniperc for 1 to 2 cm radiolucent lower calyceal renal stones to evaluate the safety and efficacy of these procedures. The results show that SFR was 73.8%, 86.1% and 95.1% for SWL, RIRS and miniperc with higher incidence of overall complications for miniperc than for SWL and RIRS (24.3% vs 7.1% and 9.3%.
Breda et al. in their study analysed 51 patients with unilateral multiple renal stones. The stone-free rates for patients with a stone burden greater than and less than 20mm were 85.1% and 100%, respectively. The authors concluded that for patients with multiple intrarenal calculi, flexible ureteroscopy with holmium laser lithotripsy may represent an alternative therapy to ESWL or PNL, with acceptable efficacy.
In our study we found that the multiple stones negatively influenced stone free rate (p.value=0.003). However when we have stone with diameter until 2 cm, even with multiple stones the overall stone free rate isn’t never below 76%. We can see clearly in the above table that when the diameter and number of stones increases, the probability of patients stone free started to decrease. Anyway even if the data is statistically significant the clinical effect is low.


Overall diameter strongly influences on stone free rate unlike the stone density.
Calyceal anatomy has a negative effect on stone clearance when angle calyx is lower than 38.2°.
In conclusion we can consider retrograde intrarenal surgery as a useful procedure also when multiple renal stones are present.
We can conclude that in our study the factors that influenced stone free rate are represented by higher stone diameter, stone number and when urinary stones in lower calyx are present by highly infundibolopielic angle. Stone density measured by NCTC can be considered useful for planning operative strategy and can influence operative time.


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