Predictive Factors for Multiple Sessions of Retrograde Intrarenal Surgery to Achieve Stone-Free Status

By Volkan Selmi, Mehmet Caniklioglu, Sercan Sari, Levent Isikay

Affiliations

1. Department of Urology, Faculty of Medicine, Yozgat Bozok University, Yozgat, Turkiye

doi: 10.29271/jcpsp.2025.08.1045

ABSTRACT
Objective: To investigate potential predictive factors for multiple sessions of retrograde intrarenal surgery (RIRS) to achieve stone-free status in patients with kidney stones.
Study Design: A descriptive study.
Place and Duration of the Study: Department of Urology, Faculty of Medicine, Yozgat Bozok University, Turkiye, from January 2015 to May 2021.
Methodology: Patients who underwent RIRS for renal stones were evaluated. Patients who were stone-free following a single intervention were labelled as Group I. Patients who required further sessions of RIRS to achieve stone-free status were labelled as Group II. The predictive factors for multiple-session RIRS to achieve stone-free status were investigated.
Results: A total of 487 patients were enrolled in the study. Stone located in the lower calyx, presence of hydronephrosis, and stone volume were identified as predictive factors for requiring multiple RIRS sessions in the logistic regression analysis (p = 0.042, p = 0.018, and p = 0.040, respectively). Patient characteristics such as gender and age, as well as stone characteristics including stone density, number, size, laterality, and operation time, were not predictive of the need for multiple intervention sessions.
Conclusion: Patients without stones in the lower calyx, without hydronephrosis, and with a low stone burden are more likely to achieve stone-free status after a single RIRS session. Otherwise, multiple sessions may be required to achieve stone-free status.

Key Words: Retrograde intrarenal surgery, Stone-free status, Nephrolithiasis.

INTRODUCTION

Percutaneous nephrolithotomy (PNL) is the gold standard treatment for stones >20 mm; however, there is an increasing trend towards retrograde intrarenal surgery (RIRS), even though it is not accepted as a first-line treatment option.¹ RIRS has been recognised as an endoscopically minimally invasive treatment option, therefore, its complication rates are lower than those of PNL.² Several researchers have reported high success rates in one session, but managing larger stones with minimally invasive treatment options may necessitate more auxiliary procedures.³

Although there are several studies which assessed stone free rates (SFRs) of RIRS for challenging stones, the predictive factors for requiring multiple sessions of intervention have not been fully evaluated.⁴ These studies revealed the predictive factors for RIRS failure.

However, the aim of this study was to investigate the potential predictive factors, such as stone and patient characteristics, associated with the need for multiple RIRS sessions to achieve stone-free status in patients with kidney stones.

METHODOLOGY

The present study protocol was approved by the Institutional Review Board of the Yozgat Bozok University, Faculty of Medicine (Approval No. 2017-KAEK-189_2021.05.26_06). The data of patients who underwent RIRS for renal stones between January 2015 and May 2021 were evaluated retrospectively. Inclusion criteria were: Age between 18 and 85 years, had one or more renal stones, and the patients who underwent RIRS to achieve stone-free status. Patients who experienced residual stone fragments following all interventions, those who required auxiliary procedures, and those with a prior double J (DJ) catheter or urinary anomaly (solitary or horse shoe kidney) were excluded.

Patients were examined using non-contrast computerised tomography (CT) and ultrasonography (USG) for the diagnosis of urolithiasis. Patients diagnosed with renal stones underwent RIRS after sterile urine samples were obtained. Stone volume was calculated using the ellipsoid formula (π x length x width x height x 0.167).⁵ In case with multiple stones, the sum of all stone volumes was used. Stone density and localisation, presence of obstruction and hydronephrosis were also evaluated using CT and intravenous pyelography (IVP), when necessary.

All operations were performed under general anaesthesia. An 11-13F ureteral access sheath (Boston Scientific Corporation, 300 Boston Scientific Way, Marlborough) was advanced to the ureteropelvic junction through the guidewire. Subsequently, the renal pelvis and collecting system were observed using the flexible ureteroscope (Flex-X2, Karl Storz, Tuttlingen, Germany/ Karl Storz, Flex X2, GmbH, Tuttlingen, Germany). Upon reaching the stone, it was dusted or fragmented using a 200 lm holmium laser probe (Ho YAG Laser, Litho DK-30, Quanta System Samarate [VA]- Italy). All patients underwent non-contrast CT after 21 days to assess stone clearance and to decide whether to remove the DJ catheter or perform another session. Patients who were stone-free after a single intervention were labelled as Group I, while those requiring another session were labelled as Group II.

Statistical Package for the Social Sciences version 25 was used for statistical analyses (IBM Inc. SPSS®, IL, USA). Continuous variables were shown as mean and standard deviation. The normality of the distribution was analysed using the Kolmogorov-Smirnov test. Normally distributed variables were compared using the Student’s t-test, and non-parametric data were analysed using the Mann-Whitney U test. The Pearson’s Chi-square test and Fisher’s exact test were used to compare qualitative data. Spearman’s correlation analysis was perfor-med to evaluate the relationships between the variables. Logistic regression analysis was used to address independent predictive factors for multiple sessions of RIRS. A p-value <0.05 was considered statistically significant.

RESULTS

A total of 487 patients, who met the inclusion and exclusion criteria, were enrolled in the study. Single session of RIRS was performed on 294 patients (Group I), while 193 patients (Group II) underwent multiple sessions of RIRS. The mean number of stones for Group I was 1.40 ± 0.626, compared to 1.75 ± 0.784 in the Group II (p <0.0001). The mean stone volume in Group II (1.251 ± 0.960 cm³) was statistically higher than that in Group I (0.722 ± 0.696 cm³) (p <0.0001). Moreover, stone density, location, presence of obstruction and hydronephrosis in the ipsilateral collecting system, and operation time were not similar between the groups (p = 0.011, p = 0.006, p = 0.001, p <0.001, and p = 0.003, respectively).

Forty-four (14.9%) postoperative complications were observed in Group I, while sixty (31%) complications were observed in Group II (p = 0.003). Four patients in Group II had minimal urinary collecting system injury and extravasation. These patients were treated with a ureteral DJ stent, and no further surgical intervention was required. Urosepsis occurred in one patient of Group I and four patients of Group II; all were treated in intensive care unit (ICU). Patient and stone characteristics, along with operation outcomes, are presented in Table I.

Stone location (especially stones located in the lower calyx), presence of hydronephrosis, and stone volume were identified as predictive factors for multiple sessions of RIRS in the logistic regression analysis. The logistic regression analysis is shown in Table II.

DISCUSSION

Various treatment options for managing stones in different patient populations have been compared with RIRS. Data in the literature reveal that SFR of RIRS performed for stones <20 mm is high and comparable to that of PNL success.^6-8 However, the SFR following RIRS was not as high as that of PNL performed on larger stones. Karakoc et al. compared RIRS and PNL for stones larger than 20 mm and reported single-session success rates were 66.6% for RIRS and 91.8% for and PNL.⁹

Table I: Patients and stone characteristics.
 

Parameters	Group I (n = 294)	Group II (n = 193)	p-values
Age (years)	47.23 ± 15.531	47.50 ± 14.419	0.849
Gender (M/F)	97/197	71/122	0.436
Mean stone number	1.40 ± 0.626	1.75 ± 0.784	<0.0001
Stone volume (cm3)	0.722 ± 0.696	1.251 ± 0.960	<0.0001
Stone density (HU)	928.15 ± 382.783	1014.14 ± 336.400	0.011
Stone laterality (R/L)	147/147	87/106	0.308
Obstruction (±)	27/267	38/155	0.001
Hydronephrosis (±)	78/216	87/106	0.000036
Stone location       Upper calyx       Middle calyx       Lower calyx       Renal pelvis       Multi-caliceal	42 38 77 114 23	15 14 69 70 25	0.006
Operation time (minutes)	41.67 ± 22.807	48.88 ± 29.928	0.003
Complications (n) (%)       Grade I       Grade II       Grade III       Grade IV       Grade V Stone-free (%)	32 11 0 1 0 100	32 20 4 4 0 100	0.0033
M: Male; F: Female; HU: Hounsfield unit; R: Right; L: Left; G: General; S: Spinal; min: Minute.

Table II: Logistic regression analysis of predictive factors for multiple sessions RIRS.

Parameters	B	S.E.	Wald	df	Sig.	Exp (B)
Age	-0.004	0.007	0.332	1	0.564	0.996
Gender	0.282	0.219	1.653	1	0.199	1.326
Laterality	-0.144	0.209	0.475	1	0.491	0.866
Stone localisation			9.889	4	0.042
Upper calyx	0.351	0.491	0.511	1	0.475	1.420
Middle calyx	0.333	0.495	0.453	1	0.501	1.396
Lower calyx	1.011	0.398	6.458	1	0.011	2.749
Multi-caliceal	0.469	0.387	1.470	1	0.225	1.598
Stone number	-0.471	0.283	2.778	1	0.096	0.624
Stone size (mm)	0.040	0.027	2.191	1	0.139	1.040
Stone density (HU)	0.000	0.000	2.570	1	0.109	1.000
Operation time	-0.006	0.005	1.716	1	0.190	0.994
Hydronephrosis	0.529	0.223	5.644	1	0.018	1.697
Stone volume	0.464	0.226	4.223	1	0.040	1.590
Constant	-1.444	0.564	6.558	1	0.010	0.236
mm: Millimetre; HU: Hounsfield unit.

Similarly, Akman et al. found that RIRS and PNL had different effects on the management of stones measuring 20-40 mm and concluded that PNL had a higher SFR than RIRS.¹⁰ Only stone-free patients were included in this study, as the deductive hypothesis was proposed to investigate the predictive factors of multiple-session interventions.

Herrera-Gonzalez et al. reported that the SFR was 79.5% in patients who had multiple stones and a cumulative stone burden of <100 mm². SFR dropped dramatically to 65.4% in patients with multiple stones and a cumulative stone burden of >100 mm².¹¹ Ozgor et al. assessed and compared the success of RIRS in patients with a single versus multiple renal stones with a burden of <300 mm², and found that the SFR was significantly higher in the single-stone group, ultimately concluding that better SFR were achieved in patients with a single renal stone of <300 mm².¹² The results of this study showed that the burden of the stone was higher in multiple-session RIRS group (p = 0.04). These findings were compatible with the current data.

El Hamed et al. evaluated the influence of stone density on the need of one or two sessions of RIRS and reported that stones with a density greater than 1000 HU were more likely to require two sessions.³ Hard stones might require more energy to be fragmented, and higher energy requirements are associated with higher time requirements to achieve stone-free status. In this study, the stone density was not similar between the groups, consistent with finding reported in the literature.

The stone location influences SFR as well as the choice of intervention modality.¹³ Literature demonstrates that PNL has the highest SFR for lower calyx stones. In a meta-analysis, Junbo et al. evaluated the treatment options for 10-20 mm lower calyceal stones and reported that PNL has the highest SFR.¹⁴ The results of this study are compatible with the literature indicating that stone location influences the frequency of multiple interventions.

Cho et al. evaluated the predictors of stone-free status following single-session RIRS and used multivariate logistic regression analysis to emphasise that for patients who experienced more than one or stones located at multiple sites had significantly lower SFRs compared to those with a single-stone.¹⁵ Parikh et al. published a single-centre RIRS experiment and concluded that a larger stone burden and lower calyceal location are important predictors of SFR.¹⁶ The outcomes of this study reported that the lower calyx stones are a significant factor for multiple-session RIRS (p = 0.011).

Ergani et al. evaluated the effect of hydronephrosis grade on RIRS outcomes and reported that the presence of hydronephrosis did not decrease operation success. However, it can be expected that the success of RIRS decreases when the hydronephrosis is severe (Grade II or higher).¹⁷ Zhao et al. analysed the predictors of SFR for RIRS in 2-3 cm stones and found that severe hydro-nephrosis was a significant predictor using multivariate analysis.¹⁸ In patients with severe hydronephrosis, a high volume of the collecting system may lead to stone translocation or displacement of large fragments to other calyces during stone fragmentation.¹⁹ In this study, the presence of hydronephrosis differed between the groups (p = 0.018).

Logistic regression analysis revealed that stone location (especially lower calyx stones), presence of hydro-nephrosis, and high stone volume were significantly associated with multiple sessions of RIRS. The logistic regression analysis outcomes were similar to those in the existing literature and are shown in Table II.

Although retrospective and single-centre design were the main limitations of this study, it is the only study in the literature which evaluates the predictive factors for multiple-sessions RIRS with a high patient population. Prospective, multi-centre clinical trials should be carried out to verify the outcomes of this study.

CONCLUSION

Anticipating success and complication rates is vital for surgeons to predict expected and unexpected events during the management of renal stones. The outcomes of this study suggest that the patients without stones in the lower calyx, without hydronephrosis, and with a low stone burden are more likely to achieve stone-free status after a single session of RIRS. However, prospective, multi-centre clinical trials are needed to verify these findings.

ETHICAL  APPROVAL:
The present study protocol was reviewed and approved by the Institutional Review Board of the Yozgat Bozok University (Approval No. 2017-KAEK-189_2021.05.26_06).

PATIENTS’  CONSENT:
Informed consent was obtained from all subjects when they were enrolled.

COMPETING  INTEREST:
The authors declared no conflict of interest.

AUTHORS'  CONTRIBUTION:
VS: Conception, design, statistical analysis, and supervision.
MC, SS: Data acquisition.
VS, MC: Data analysis and interpretation.
VS, LI: Drafting of the manuscript.
LI: Critical revision of the manuscript for scientific and factual content.
All authors approved the final version of the manuscript to be published.

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