Which Should be Preferred for Moderate-Size Kidney Stones? Ultramini Percutaneous Nephrolithotomy or Retrograde Intrarenal Surgery?

Abstract

Purpose:

Comparison of effectiveness and safety of ultramini percutaneous nephrolithotomy (UMPNL) and retrograde intrarenal surgery (RIRS) in treatment of moderate-sized renal stones.

Material and Methods:

The patients scheduled for surgery attributable to renal stones with the greatest diameter of 10 to 25 mm were prospectively analyzed. Patients were randomized into groups with tossing a coin method. The patients who had UMPNL and RIRS were defined as Group I and Group II, respectively. The groups were compared for demograhic data, stone characteristics, operative and postoperative data, stone-free status, and the complications. Student's t-test and Pearson's Chi square tests were used for statistical analysis. p < 0.05 was considered as statistically significant.

Results:

There were 30 patients in Group I, and 43 patients in Group II. The groups were similar for age, gender, side of the stone, and surface area characteristics of the stone (p = 0.194, p = 0.470, p = 0.990, and p = 0.487, respectively). Stone-free rate was 80% (n = 24) in UMPNL, and 74.4% (n = 32) in RIRS (p = 0.579). Modified Clavien Classification Grade 1 to 2 and 3A to 3B complications were similar in two groups (p = 0.959 and p = 0.192, respectively). Comparison of stone-free rates was 93.3% in UMPNL, and 42.9% in RIRS groups for lower pole stones (p = 0.009). Groups I and II were significantly different for visual analog scale scores for postoperative pain (4.73 ± 1.25 vs 2.30 ± 1.12), hospital stay (2.46 ± 3.02 vs 1.37 ± 1.48 days), and time to return to normal daily life (11.26 ± 5.55 vs 6.65 ± 4.30 days) (p < 0.001, p < 0.001, and p < 0.001, respectively).

Conclusion:

Both UMPNL and RIRS procedures are effective and safe methods in treatment of middle-sized renal stones. However, UMPNL is more effective than RIRS in treatment of lower pole stones. RIRS is more advantageous when loss from work is taken into consideration.

Introduction

Open surgery for renal stones has been replaced by minimally invasive techniques including shockwave lithotripsy (SWL), percutaneous nephrolithotomy (PNL), and retrograde intrarenal surgery (RIRS) in parallel with the technological advancements.^1

–4 Each procedure has its own advantage and disadvantages, and preference of the technique is one of the most debated subjects in current endourological practice.

Although PNL is one of the most frequently preferred techniques owing to its high stone-free rates, it is not considered as a minimally invasive technique by most authors owing to its major complications including bleeding, organ injury, and sepsis.^5
–7 Some modifications have been done such as reducing the tract diameter and using miniaturized equipment to decrease the complication rates of this successful technique. The technique has been renamed in the light of those modifications: standard PNL indicates a tract diameter of 24 to 30F, mini-PNL (MPNL) indicates a tract diameter smaller than 18F, and ultramini PNL (UMPNL) indicates a tract diameter ≤14F.^8

–11

The indications of RIRS has increased in the recent years, the technique found a place in the treatment of renal stones, and it has been regarded as the first option in treatment of moderate-sized kidney stones together with SWL.^4,12,13 However, this technique has its own limitations, and it has been known that its success rate is lower in lower calix stones when the infundibulopelvic angle is narrow.^14,15 Preference of RIRS or minimally invasive PNL techniques such as UMPNL in moderate-sized kidney stones, and effectiveness and safety of those techniques under certain circumstances have been currently debated.^9,10

In this study, we aimed to investigate effectiveness and safety of UMPNL and RIRS procedures along with their effects on the patients' lives in cases with renal stones 10 to 25 mm at their biggest diameter, when previous SWL was unsuccessful, or it could not be used due to some negative conditions. We also investigated the effectiveness of those techniques in lower pole stones.

Materials and Methods

After approval of the study protocol by the local ethics committee, the patients admitted to our clinic and diagnosed with renal stones and scheduled for surgery between March and September 2015 were prospectively analyzed. A total of 73 patients with stone sizes of 10 to 25 mm, and had RIRS or UMPNL procedures were included in the study. Randomization for UMPNL or RIRS procedures was done with tossing a coin method, and one surgeon performed UMPNL, and another performed RIRS. Both are highly experienced surgeons. Kidney abnormality, bleeding diathesis refractory to treatment, obesity (>30 kg/m²), skeletal deformity, previous kidney surgery, and untreated urinary tract infection were the exclusion criteria.

An appropriate calix access was obtained in UMPNL, then Amplatz renal dilator set was used for dilation up to 14F, and a 17-cm renal access sheath sized 14F (Boston Scientific) was placed. A 6/7.5F nephroscope (Wolf ureterorenoscope) was used to view inside the kidney, and the stones were fragmented with holmium laser lithotripter (550 μm, Sphinx) until they were suitable for spontaneous passage. The stone-free status of the kidney was controlled with nephroscopic visualization and fluoroscopy, and an antegrade Double-J stent, or a reentry catheter was placed by taking stone-free status and bleeding status into consideration, or the procedure was ended tubeless.

RIRS procedure was done using a 9.5/11.5F (Cook Medical) ureteral access sheath, a 7.5F flexible ureterorenoscopes (f-URS) (Storz Flex-x²), and a holmium Yag laser lithotripter (272 μm, Sphinx). Following completion of fragmentation, ureter was observed all along its length to see any ureteral injury. Double-J stent was not routinely placed after the procedure, and it was placed if there was mucosal injury or edema, or the duration of the procedure was long. Ureteral Double-J stents were removed 2 to 4 weeks after surgery.

The patients who had UMPNL were defined as Group I, and the ones who had RIRS were defined as Group II. The groups were compared for age, gender, side of the stone, the surface area of the fragmented stone, duration of surgery, duration of fluoroscopy during surgery, postoperative pain, hospital stay, time to return to normal daily life, stone-free status, stone-free status in relation with the localization of stone, and the complications.

Intravenous urography and low-dose non-contrast computed tomography (CT) were used to determine the side, size, and localization of the stone before surgery. The surface area of the fragmented stone was calculated from CT images as follows: “Surface area of the stone = length × width × 0.25 × π”.^4,16 Postoperative pain was determined by visual analog scale (VAS), asked by the same physician to all patients 2 hours after surgery. Return to normal daily life was determined by asking the patients the time between discharge from hospital and return to work. Stone-free status was determined with low-dose non-contrast CT obtained one month after surgery. Absence of any stones, or stone fragments smaller than 3 mm were considered as the stone-free status. “Modified Clavien Classification” reported by Dindo and Clavien in 2004 was used to grade the complications.¹⁷

Statistical analysis

The analysis of data was done using SPSS for Windows, version 11.5 (SPSS, Inc., Chicago, IL). Descriptive statistics for the nominal variables and the variables with normal distributions were presented as the number of cases and (%), and mean ± standard deviation, respectively. The significances of the differences between the groups in terms of mean values were analyzed with Student's t-test. Nominal variables were analyzed with Pearson's chi-square or Fisher's exact tests. p < 0.05 was considered as statistically significant.

Results

The demographic characteristics of the patients including age, gender, and the laterality of the stones were similar in 30 patients in group I who had UMPNL, and 43 patients in group II who had RIRS (p = 0.194, p = 0.470, and p = 0.990, respectively) (Table 1). The mean stone surface area was 185.86 ± 88.29 mm² in Group I, and 181.70 ± 114.18 mm² in Group II (p = 0.487); therefore the preoperative stone burdens of UMPNL and RIRS groups were similar (Table 1). The groups were different for localizations of the stones (p = 0.020) (Table 1). It was determined that 23.3% (n = 7) of the patients in Group I, and 34.9% (n = 15) of the patients in Group II had previous unsuccessful SWL procedures (p = 0.290) (Table 1).

Table 1.

Demograhic Data and Stone Characteristics

	Group I	Group II	p
No. of patients	30	43
Age (years)	43.73 ± 14.62	48.72 ± 16.87	0.194
Male/female	21/9	20/23	0.470
Mean stone size (mm²)	185.86 ± 88.29	181.70 ± 114.18	0.487
Preoporative SWL	7 (23.3%)	15 (34.9%)	0.290
Stone laterality
Right/left	14/16	20/23	0.990
Stone location
Pelvis	12 (40%)	23 (65.7)
Upper pole	0 (0%)	2 (4.7%)
Middle pole	0 (0%)	3 (7%)	0.020^a
Lower pole	15 (50%)	7 (16.3%)
Multicaliceal	3 (10%)	8 (18.6%)

Significant at p < 0.05.

SWL = shockwave lithotripsy.

Comparison of the groups for stone-free status revealed that 80% (n = 24) of UMPNL (Group I) patients, 74.4% (n = 32) of RIRS (Group II) patients were stone free (p = 0.579) (Table 2). According to “Modified Clavien Classification,” there were Grade 1 and 2 complications in 2 (6.7%) patients in group 1, and in 3 (7%) patients in Group II (p = 0.959). Grade 3A and 3B complications were seen in 5 (16.7%) and 3 (7%) patients in Groups I and II, respectively, without any significant difference between two groups (p = 0.192) (Table 2). Grade 4 and 5 complications did not develop in any patients.

Table 2.

Comparison of Operative and Postoperative Data

	Group I	Group II	p
Mean fluoroscopy time (seconds)	185.76 ± 130.94	57.20 ± 25.43	<0.001^a
Mean operative time (minutes)	54.53 ± 23.09	59.41 ± 15.78	0.319
Mean hospitalization time (day)	2.46 ± 3.02	1.37 ± 1.48	<0.001^a
VAS Score	4.73 ± 1.25	2.30 ± 1.12	<0.001^a
Return to normal daily life (day)	11.26 ± 5.55	6.65 ± 4.30	<0.001^a
Total stone-free rate (%)	24 (80)	32 (74.4)	0.579
Stone-free rate for pelvis (%)	10 (83.3)	21 (91.3)	0.482
Stone-free rate for lower pole (%)	14 (93.3)	3 (42.9)	0.009^a
Stone-free rate for multicaliceal (%)	0 (0)	5 (62.5)	0.064
Complication, clavien I-2 (%)	2 (6.7)	3 (7)	0.959
Complication, clavien 3A-3B (%)	5 (16.7)	3 (7)	0.192

Significant at p < 0.05.

VAS = visual analog scale.

Comparison of the groups for stone-free rates in relation with the localization of the stone revealed stone-free status for lower pole stones in 14 (93.3%) patients in Group I, and in 3 (42.9%) patients in Group II (p = 0.009). The numbers of stone-free patients were 10 (83.3%) and 21 (91.3%) for pelvic stones (p = 0.482), and 0 (0%) and 5 (62.5%) in multicaliceal stones (p = 0.064) in Groups I and II, respectively. There was a significant difference between the groups for lower pole stones (Table 2). There were no patients with upper or middle pole stones in Group I; therefore, the groups could not be compared for those two localizations.

The duration of fluoroscopy during surgery was 185.76 ±130.94 seconds in Group I, and 57.20 ± 25.43 seconds in Group II, with a significant difference in between (p < 0.001). The mean duration of procedure was 54.53 ± 23.09 minutes in Group I, and 59.41 ± 15.78 minutes in group II, and it was similar in UMPNL and RIRS groups (p = 0.319) (Table 2).

VAS pain scores, hospital stay, and time to return to normal daily activities were significantly different when Groups I and II were compared (p < 0.001, p < 0.001, and p < 0.001, respectively) (Table 2).

Discussion

Lower cost and less loss from work is targeted in renal stone disease due to its tendency for recurrence and high prevalence, and the treatment modalities aimed to be less invasive, and decrease morbidity to a minimum since ancient times.^1,7,8,18

One of the cornerstones in minimally invasive stone surgery has been definition of PNL procedure, and definition of PNL types in relation with the width of the tract.^2,4,9 Although MPNL procedure was defined in European Association of Urology (EAU) guidelines, and its success and place in the treatment of renal stones were proven by meta-analyses and randomized controlled studies, UMPNL that uses a tract with a diameter of 11 to 14F is a new technique, and it has been investigated in only a few studies.^4,8,11 A meta-analysis by Zhu et al.⁸ reported similar stone-free rates with MPNL and standard PNL in 2015, and the authors pointed out the advantages of less invasive techniques due to less pain, shorter hospital stay, less decrease in hemoglobin, and less need for blood transfusion in MPNL.

Advancements in flexible ureterorenoscopes (f-URS) and laser lithotripters made another minimally invasive technique, RIRS, a recommended and preferred technique in urinary system stone disease, and it was compared with standard PNL and MPNL for its success and complications.^19
–21 A meta-analysis on the treatment of stones >2 cm reported similar stone-free rates for RIRS and standard PNL, and RIRS was found superior to PNL in terms of shorter hospital stay and less bleeding.²²

UMPNL was first described in a report from India.⁹ Its stone-free rate was reported as 97.2%, duration of surgery was reported as 59.8 ± 15.9 minutes, hospital stay was reported as 3.0 ± 0.9 days, and the complication rate was reported as 16.7% in 36 renal stones smaller than 20 mm.

In 2015, Wilhelm et al.¹⁰ compared UMPNL and RIRS in two groups both consisting of 25 patients with stone sizes of 10 to 35 mm, and found two methods similar for stone-free rates (%92 vs %96), cumulative analgesic consumption score (CACS) (6.8 vs 6.96), Freiburg index of patient satisfaction (1.73 vs 1.67), and “Clavien” Grade 2 to 3 complications (16% vs 4%). However, duration of surgery (130.12 vs 98.52 minutes) and hospital stay (91.5 vs 67.2 hours) were found significantly longer in UMPNL, and the authors concluded that two surgical procedures were safe and effective methods in treatment of middle-big-sized kidney stones, and the preference for the procedure depended on technical equipment and experience of the surgeon.

A study performed in Germany in 2015 retrospectively analyzed the patients that had UMPNL or RIRS due to renal stones with the size of 10 to 20 mm, and did not find any difference between two methods for stone-free rates (84% vs 87%), complications (7% for both), duration of surgery (121 vs 102 minutes), or hospital stay (2.3 vs 2 days), but UMPNL was found to be more advantageous due to its lower cost (665 vs 1160 Euros).²³

UMPNL has been reported as a safe and effective method, and more advantageous and safer than standard PNL and micro PNL since it is less invasive and results in lower intrarenal pressure. Dede et al. reported stone-free rate as 82% in children.¹¹

Despite its different terminology, supermini PNL (SMPNL) performed on 146 patients using a tract diameter of 10 to 14 F is the largest series on this subject. One hundred forty-one of 146 patients completed their treatment with this method, the authors reported mean stone size as 22 mm, duration of surgery as 45.6 minutes, mean hospital stay as 2.1 days, stone-free rate as 90.1%, complication rate as 12.8% (<2 Clavien), and need for transfusion as 0%, and they concluded that SMPNL was an effective and safe method in stones <25 mm. The authors also stated that only 19.8% of the patients needed Double-J stent, and nephrostomy catheters were used in only 5.7% of the patients, and the majority of the patients (72.3%) did not need any catheters.²⁴

In our study, we investigated effectiveness and safety of UMPNL and RIRS procedures in 73 patients with kidney stones sized 10 to 25 mm. We found that those two procedures were similar for providing a stone-free state (p = 0.579), and the analysis of “Modified Clavien” Grades 1 and 2, and 3A and 3B separately revealed that they were similar in two groups (p = 0.959 and p = 0.192, respectively). In addition, we found the stone-free rate as 80% in UMPNL, and this was in conjunction with the studies in the literature, although they are small in number.^10,11,23

EAU guidelines and various authors described the treatment options specific to lower pole stones, and reported the success rates in those stones separately.^4,20,25 Therefore, we analyzed our stone-free rates in UMPNL and RIRS procedures in relation with the localizations of the stones. As shown in other studies on standard PNL,^26,27 we found a significantly higher stone-free rate (93.3%) in lower pole stones with UMPNL when compared to RIRS. Similarly, in 2011 Unsal et al.²⁶ suggested that PNL procedures should be the first treatment option in lower pole stones bigger than 10 mm in size since they had high stone-free rates (93.3%). A meta-analysis performed in 2015 included six randomized and eight nonrandomized studies that compared PNL, RIRS and SWL in treatment of lower pole stones, and reported that PNL was superior to RIRS and SWL in lower pole stones.²⁷

In our study, UMPNL and RIRS procedures were found similar for duration of surgery, however, RIRS was found to be more advantageous than UMPNL when duration of use of fluoroscopy during surgery was taken into consideration (57.20 ± 25.43 vs 185.76 ± 130.94 seconds), a parameter that was not been studied before. A multicenter study that compared MPNL and RIRS in the pediatric age group reported RIRS to be more advantageous than MPNL due to shorter fluoroscopy duration required during surgery.²⁸

We found that postoperative pain was significantly less (p < 0.001), and hospital stay was significantly shorter (p < 0.001) in RIRS when compared to UMPNL. A relatively subjective parameter, time to return to normal daily activities, was found as 6.65 ± 4.30 days in RIRS, and it was significantly shorter compared to UMPNL (p < 0.001).

The different sizes of laser fibers that were used may be considered as another variable that can change the results but Kronenberg et al.²⁹ compared the effectiveness of laser fibers with different diameters. They found that the fiber diameter did not effect the fragmentation volume.

The limitation of our study is difference in the distribution of the localizations of the stones in two groups and not performing flexible nephroscopy at the end of the procedure. We used 14F sheath for UMPNL but our flexible nephroscope (Wolf) has 15F outer diameter. This is a technical limitation for performing flexible nephroscopy at the end of the procedure. On the other hand, it is a prospective randomized study, and there are only a few studies in the literature on this subject.

Conclusion

The results of this study indicated that RIRS and UMPNL were two preferable techniques with similar success and complication rates in the treatment of moderate- size renal stones. RIRS should be the preferred method because of low VAS scores and return more quickly to daily life. UMPNL should be preferred for lower caliceal stones due to higher success rates. Despite all those considerations, the results of few studies in the literature as well as the results of our study on safety and effectiveness of UMPNL should be supported by further randomized controlled studies and meta-analyses, as the principles of evidence-based medicine necessitate.

Footnotes

Author Disclosure Statement

No competing financial interests exist.

Abbreviations Used

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