Contemporary Management of Medium-Sized (10–20 mm) Renal Stones: A Retrospective Multicenter Observational Study

Abstract

Purpose:

To evaluate contemporary management approaches to medium-sized (10–20 mm) renal stones.

Patients and Methods:

A total of 935 patients treated for medium-sized renal stones (10–20 mm) between July 2012 and March 2014 were included in the study program. Contemporary minimally invasive approaches applied in the management of such stones were evaluated and compared.

Results:

The cohort consisted of 561 male (60%) and 374 female (40%) patients. Of the 935 patients with medium-sized renal calculi, 535 (57.2%) were treated with shockwave lithotripsy (SWL), 201 (21.4%) with retrograde intrarenal surgery (RIRS), 110 (11.7%) with minimally invasive percutaneous nephrolithotomy (miniperc), and the remaining 89 (11.7%) patients with micropercutaneous nephrolithotomy (microperc). In the SWL group, stones were located mostly in the pelvis (51%), while in the miniperc and microperc groups, they were located mainly in the lower pole (46%, 53%, respectively). Stone-free rates after a single session were 77.2%, 86.1%, 88.8%, and 83.6% in the SWL, RIRS, microperc, and miniperc groups, respectively. Although no serious complications (above Clavien level III) were noted in any of the groups evaluated, Clavien I to II complications were common in the miniperc group.

Conclusion:

Although SWL is the preferred treatment option for patients with medium-sized (10–20 mm) renal stones, endourologic methods also have been found to have a significant role. Relatively lower complication rates along with higher stone-free status observed with the RIRS technique compared with percutaneous approaches have made this method a valuable option in the management of such stones in recent years.

Introduction

Shockwave lithotripsy (SWL), retrograde intrarenal surgery (RIRS), and minimally invasive percutaneous nephrolithotomy (PNL; miniperc) have been applied successfully in the management of medium-sized (10–20 mm) renal stones.¹ Because of the success and safety of the procedure, SWL has been the option of choice in the management of renal stones of up to 20 mm for many years; however, the drawbacks of this approach include some well-known limitations, such as a lower success rate in lower pole stones, the need for multiple sessions, and ongoing controversies regarding its safety in pediatric renal stones.^1

–4

In the last decade, technologic advances and increasing interest as well as experience of urologists in endourologic treatment modalities have led to the more common performance by urologists of minimally invasive endoscopic methods.^5,6 Consequently, an increasing number of recently published articles evaluating the management of these stones with endourologic approaches have served to further justify their importance.^7
–9 Furthermore, in addition to miniperc and RIRS techniques, a novel option, micropercutaneous nephrolithotomy (microperc), has been introduced to manage renal stones clinically in a less invasive manner.^10
–12

In this study, with focus on the contemporary management of medium-sized (10–20 mm) renal stones, we aimed to evaluate the management approaches to these stones in four high-volume departments. The success rates, complications, advantages, and limitations of all available contemporary management modalities were evaluated in this retrospective multicenter observational study.

Patients and Methods

A total of 935 patients treated for medium-sized renal stones (10–20 mm) in four high- volume stone departments (≥250 endoscopic kidney stone interventions annually) between July 2012 and March 2014 were included to this study program. Stone size was assigned by calculating the longest axis of the kidney stone visible on the CT scan. In patients with multiple stones, the sum of the longest diameters constituted the stone size. Medical records including the physical examination findings, urine analysis and culture, biochemistry, complete blood cell count, and CT scan data were thoroughly reviewed.

All of the treatment options for medium-sized stone management were discussed with the patient, but SWL was recommended as the priority according to the European Association of Urology guidelines 2014.¹ On the other hand, we provide endourologic procedures as an alternative treatment options to all patients and decide on the type of treatment modality according to the stone characteristics or patient preference mentioning complication and success rates of all procedures.

SWL

All SWL-related procedures were conducted as an outpatient procedure. All SWL devices used in these centers had an electromagnetic SW generating system (Dornier Compact Sigma, Medtech, Germany; Dornier MPL-5000, Germany; Storz Medical Modulith SLK, Germany). Regarding the application of SWL, there were no local differences. Although power settings and frequency might vary between centers, the treatment was generally initiated at a lower power frequency, 12 kV, and increased to 20 kV, with a maximum of 3000 shockwaves in adults and 2000 shockwaves in children per session.

To determine the presence and size of stone fragments, kidney-ureter-bladder (KUB) radiography and sonography were performed in all patients 1 week later. A noncontrast CT was performed in case of suspicion with respect to the presence of stone fragments. While the symptomatic and/or obstructing stones that could not be fragmented with SWL were further disintegrated with endourologic intervention, asymptomatic calculi were considered for further monitoring.

RIRS

All procedures were performed under general anesthesia with the patient in the lithotomy position. Under fluoroscopic guidance, a hydrophilic guidewire was inserted during semirigid ureteroscopic evaluation of the involved ureter. In cases in which the ureteral access sheath (UAS) and/or ureteroscope could not be further advanced into the ureter, balloon dilation, passing the ureterorenoscope over a guidewire or passive dilation of the ureteral orifice was used according to the preference of the urologist. In all centers, holmium:yttrium-aluminum-garnet (YAG) laser was used for stone fragmentation. While stone fragmentation or dusting depended on the stone type or surgeon preference, all renal stones were fragmented to the required size for spontaneous passage rather than removing all of the fragments by basket catheter. Postoperative Double-J stent insertion and timing of removal differed between departments and surgeons.

PNL

In all centers, the procedure was performed under general anesthesia with the patient in the lithotomy position, and a ureteral catheter was inserted during rigid cystoscopy. Then, the patient was brought into the prone position. A mixture of saline and opaque material was flushed through the ureteral catheter, and the appropriate kidney puncture was made under fluoroscopic guidance. Amplatz, metal, or balloon dilators up to 20F (20F or lower), depending on the preference of the surgeon, and a nephroscope were used. A pneumatic lithotripter or ultrasonic lithotripter was used for stone fragmentation, and fragmented pieces were extracted by grasper or triceps forceps in patients who underwent miniperc. After completion, placement of a nephrostomy tube was dependent on the duration and complexity of the intervention as well as surgeon preference. Patients were discharged from the hospital on postoperative removal of the tube.

Microperc

After ureteral catheter placement with the patient in the lithotomy position under general anesthesia, the microperc procedure was performed with the patient in the prone position. Percutaneous access was achieved using a 4.8F microperc needle (PolyDiagnost, Pfaffenhofen, Germany). Access to the stone with “all-seeing needle” optical, fluoroscopic, or ultrasonographic guidance differed between the urologists. A surgeon-controlled irrigation system (IP 200, PolyDiagnost, Pfaffenhofen, Germany) was used for irrigation, and fragmentation was performed with a holmium:YAG laser. Double-J or ureteral catheter insertion was applied based on the course of the procedure and surgeon preference.

Statistical analysis

Descriptive statistics including mean, standard deviation, and frequency values were used in data analysis. The distribution of variables was checked by Kolmogorov-Smirnov test. In the analysis of quantitative data, Kruskal-Wallis and Mann-Whitney U test were used. In the analysis of qualitative data, chi-square tests were used. The Statistical Package for the Social Sciences (SPSS) 22.0 program was used in the analysis.

Results

Among the patients treated for renal stones and evaluated retrospectively, a total of 935 patients treated for medium-sized stones, with a mean age of 41.7±17 (1.5–84) years, were included to the study. The cohort consisted of 561 male (60%) and 374 female (40%) patients. The mean stone size was 14.6±3.3 mm, and of these stones, 53.2% were located in the right kidney. Of these patients, 535 (57.2%) underwent SWL, 201 (21.5%) RIRS, 110 (11.8%) miniperc, and 89 (9.5%) microperc (Fig. 1). Patient and stone demographics are presented in Table 1. The mean stone size was the smallest in the microperc (13.4±2.5 mm) group, while the largest mean stone size was noted in the miniperc (16.8±3.3) group (P=0.00).

FIG. 1.

The distribution of patients according to treatment. SWL=shockwave lithotripsy; RIRS=retrograde intrarenal surgery; miniperc=minimally invasive percutaneous nephrolithotomy; microperc=micropercutaneous nephrolithotomy.

Table 1.

Patient and Stone Demographics

	SWL	RIRS	Miniperc	Microperc	Total
Number of patients	535 (57.2%)	201 (21.5%)	110 (11.8%)	89 (9.5%)	935
Age of patients	44.43±14.8 (1.5–77)	44.28±16.28 (2–84)	25.05±20.75 (2–67)	40.1±20.32 (1.5–80)	41.7±17.6 (1.5–84)
Sex
Female	187 (35%)	90 (44.8%)	54 (49.1%)	43 (48.3%)	374 (40%)
Male	348 (65%)	111 (55.2%)	56 (50.9%)	46 (51.7%)	561 (60%)
Side of stone
Right	272 (50.8%)	122 (60.7%)	54 (49.1%)	49 (55.1%)	497 (53.2%)
Left	262 (49%)	79 (39.3%)	56 (50.9%)	40 (44.9%)	437 (46.7%)
Bilateral	1 (0.2%)	None	None	None	1 (0.1%)
Number of stone
Solitary	535 (100%)	174(86.6%)	110 (100%)	83 (93.3%)	902(96.5%)
Multiple	None	27(13.4%)	None	6 (6.7%)	33 (3.5%)
Location of stone
Renal pelvis	273 (51%)	68 (33.8%)	36 (32.7%)	23 (25.8%)	400 (42.8%)
Upper pole	40 (7.5%)	10 (5%)	10 (9.1%)	3 (3.4%)	63 (6.7%)
Mid calix	92 (17.2%)	41 (20.4%)	13 (11.8%)	9 (10,1%)	155 (16.6%)
Lower pole	130 (24.3%)	55 (27.4%)	51 (46.4)	48 (53.9%)	284 (30.4%)
Lower pole+midcalix	None	21 (10.4%)	None	1 (1.1%)	22 (2.4%)
Upper pole+renal pelvis	None	1 (0.5%)	None	None	1 (0.1%)
Lower pole+renal Pelvis	None	4 (2%)	None	3 (3.4%)	7 (0.7%)
Upper+lower pole	None	1 (0.5%)	None	2 (2.2%)	3 (0.3%)
Mean stone diameter (mm)	14.44±2.9	14.15±3.7	16.81±3.3	13.37±2.5	14.56±3.2
Operative time (min)	None	89.6±31.4	55±44.6	46.3±28.7	67±40.8
Transfusion	None	None	8 (7.2%)	3 (3.3%)	11 (1.2%)
Complication
Hematuria	17 (3.2%)	None	17 (15.5%)	None	34 (3.6%)
Fever	8 (1.5%)	2 (1%)	5 (4.5%)	1 (1.1%)	16 (1.7%)
A-V fistula	None	None	None	1 (1.1%)	1 (0.1%)
Renal colic	None	None	None	4 (4.5%)	4 (0.4%)
Others	None	None	2 (1.8%)	None	2 (0.2%)
Total	25 (4.7%)	2 (1%)	24 (21.8%)	6 (6.7%)	57 (6.1%)
Stone-free rate	77.2%	86.1%	83.6%	88.8%	81.0%
Auxiliary treatment	123 (22.8%)	20 (10%)	4 (3.6%)	10 (11.2%)	157 (16.8%)
Stone-free rate	498 (93.1%)	192 (95.5%)	101 (91.8%)	83(93.3%)	874 (93.5%)
Stone-free+CIRF	507 (94.8%)	192 (95.5%)	103 (93.6%)	83(93.3%)	885 (94.7%)

SWL=shockwave lithotripsy; RIRS=retrograde intrarenal surgery; miniperc=minimally invasive percutaneous nephroliothotomy; macroperc=micropercutaneouys nephrolithotomy; A-V=arteriovenous; CIRF=clinically insignificant residual fragments.

The mean duration of the interventions in all minimally invasive approach groups (except the SWL procedure) was 67±40.8 minutes (10–200 min), and the mean operative duration was the longest (89.6 min) in the RIRS group (P=0.00). There was no statistically significant difference with respect to the hospitalization time.

An evaluation of the treatment modalities applied according to sex revealed that when compared with SWL and RIRS, the majority of female patients were treated with the micro- and miniperc techniques (P=0.003). Regarding the location of the stones treated, in the SWL group, stones were located primarily in the pelvis (51%), while in the miniperc and microperc groups, they were located in the lower pole (46.4%, 53.9%, respectively); in the RIRS group, they were more frequently in the pelvis and lower pole positions (33.8% and 27.4%, respectively). Stone-free rates (SFRs) after the first sessions of SWL, RIRS, miniperc, and microperc were 77.2%, 86.1%, 83.6%, and 88.8%, respectively (P=0.006).

Of the patients treated with SWL, management was unsuccessful in 22.8% of the cases, and other treatment options were considered. One to five SWL sessions were used in 21.5%, 26.9%, 46.0%, 4.7%, and 0.9% of patients in the study groups, respectively. Auxiliary treatment rates were significantly higher in the SWL and lower in miniperc arms (23%, 10%, 11.2%, and 3.6% for SWL, RIRS, microperc, and miniperc groups, respectively; P=0.00).

Global SFR for the initial treatment was 80.1% and 81.4% for lower and nonlower pole stones, respectively. There were no statistical differences between lower and nonlower pole stones. When evaluated according to treatment modality, while in patients with lower pole stones, the SWL success rate was significantly decreased (P<0.005), the SFR in the RIRS, microperc, and miniperc groups did not show any differences between lower and nonlower pole stones.

While UAS was used in 98% of the cases treated with RIRS, passive dilation was necessary in 8.8% of the patients. Although the holmium:YAG laser was used in all patients undergoing RIRS and microperc procedures, laser and pneumatic lithotripters were used during the miniperc procedure. In general, no complications above Clavien level III developed. Angioembolization was needed in one patient undergoing the microperc procedure because of atrioventricular fistula formation. Clavien I to II complications were more evident in the miniperc group. Intravenous transfusion was necessary in three (3.4%) patients in the microperc group and in eight (7.3%) patients in the miniperc group. No transfusion was needed in patients in the SWL and RIRS groups (P=0.001).

Stone-free status evaluation methods for the whole cohort were KUB radiography, ultrasonography (US), KUB and US, CT, fluoroscopy, and fluoroscopy and US. Preferences, however, were KUB radiography for SWL patients (77.9%), fluoroscopy for RIRS and miniperc patients (69.2%–87.3%), and combined KUB and US for microperc patients (69.7%).

Discussion

Optimal management of kidney stones measuring 10 to 20 mm has been controversial for urologists, and clinical introduction of minimally invasive treatment approaches has made the decision-making more demanding than ever. As an anesthesia-free alternative, SWL has been commonly applied as a practical, safe, noninvasive, and effective method in the majority of these stones. Despite all these advantages, however, this technique achieves good results at the expense of repeated treatments in a certain percentage of cases, making the total duration of the treatment longer than with the other approaches. In addition, passage of the fragmented calculi may cause colic pain and urinary symptoms that may pose further discomfort for the patients.

In light of these disadvantages, to achieve a completely stone-free status in a shorter period, urologists have tended to perform other minimally invasive stone-removal procedures (i.e., ureteroscopy, percutaneous approach) in the management of these stones. In addition to the clinical introduction of laser technology, technologic advances have enabled the use of small-caliber, more flexible ureteroscopes, UAS, and stone retrieval devices during ureteroscopic stone removal. Again, smaller scopes in the percutaneous approach have minimized the extent of renal trauma during PCNL, enabling high success rates with relatively lower complications. All these advances along with increasing experience in this field of urology have resulted in widespread recognition of endourologic stone management throughout the world.

Based on the literature data reporting satisfactory results obtained with minimally invasive endourologic approaches in kidney stones measuring 10 to 20 mm, in this study, we aimed to evaluate the management techniques applied in four different high-volume departments in an attempt to outline the current contemporary approach to the removal of such stones.¹³ Our findings demonstrated that 57.2% of these patients underwent SWL treatment; 60% of the general cohort was male. The percentage of female patients undergoing percutaneous interventions (microperc and miniperc), however, was relatively higher than in the SWL and RIRS arms. To our best knowledge, there is no information available in the relevant literature about sex preference and the reason for the female predominance in percutaneous interventions when compared with SWL or RIRS procedures.

Because the ultimate aim of stone removal procedures is to achieve a completely stone-free status with limited or no morbidity, the size of the treated stone has been the most crucial factor in this regard. Evaluation of the size of the treated stone in all groups clearly demonstrated that the outcome of the preferred modality seemed to be related to stone size, and the mean stone size in the microperc group was smaller than in the other treatment groups. This can be considered as an inherent outcome of the microperc technology and design.

In addition, our retrospective study showed that the stone location is the unique variable determining the urologist's preference in the management of medium-sized kidney stones. Evaluation of our data in this regard again indicated that SWL and RIRS have been applied in the majority of pelvic stones; however, in lower pole stones, miniperc and microperc techniques were commonly preferred. In our study, the SFRs for the initial treatment were 80.1% and 81.4% for lower and nonlower pole stones. There was no statistical difference between lower and nonlower pole stones.

Evaluation of the cases based on the treatment modality applied revealed that the SWL success rate was significantly decreased in patients with lower pole stones (P<0.005), while the SFR for RIRS, microperc, and miniperc patients did not show any differences between lower and nonlower pole stones. Similar results were achieved in the Global Clinical Research Office of the Endourological Society Ureteroscopy study, which reported no differences in the SFRs between lower pole and nonlower pole stones.⁵

Evaluation of the treatment modalities preferred based on stone location gives important implications about the approaches favored by both urologists and patients. Accordingly, while SWL and RIRS are the more commonly preferred modalities in renal pelvic calculi, miniperc and microperc techniques were the treatment of choices in the majority of patients with lower pole stones. The success rates of SWL in lower pole stones is reported in the literature on a vast scale ranging from 25% to 85%, and the shortcomings in the lower pole stones are well known.^{5,6,14

–19}

The effective use of the optic needle with laser created an all-seeing needle, which enables micropercutaneous intervention for renal stones.²⁰ Microperc, which has shown promising initial results,^12,21,22 was applied in our study to 11.7% of the patients. Although the SFR was comparable to that of the miniperc and RIRS arms, the stone size in the microperc group was relatively smaller than that of the other groups. Further studies will both foster and clarify the status of microperc in stone treatment.

Auxiliary treatment rates were significantly higher for patients in the SWL arm (P=0.00). While it is less invasive compared with other stone treatment modalities, the high rate of multiple treatment sessions and need for auxiliary treatments need to be properly interpreted by urologists.

The main drawbacks of our study were discrepancy of the patient number between the treatment options and the lacking of stone locations uniformity. Moreover, the multicentric design of the study, even in high-volume centers, could be considered another limitation. On the other hand, taking into account the nature of an observational study might have minimized these disadvantages of our article.

Our current data clearly show that although SWL is the preferred treatment option in medium-sized renal stones, endourologic techniques have gained a significant role in recent years. The evident lower complications observed in the RIRS group compared with percutaneous approaches along with higher SFR justifies that RIRS has proven itself in recent years to be a preferred option. SWL, RIRS, miniperc, and microperc are competitive techniques, and each has its own unique advantages and disadvantages. Judicious use of all the available options will surely increase the success rates and lower the complications in medium-sized renal stone management.

Footnotes

Author Disclosure Statement

No competing financial interests exist.

Abbreviations Used

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