Accuracy of R.E.N.A.L. nephrometry score in predicting perioperative outcomes of minimally invasive partial nephrectomy: impact of different surgical techniques

Introduction

Globally, renal tumours are the sixth most common cancer in men and the ninth most common in women, accounting for 5% and 3% of all tumour diagnoses, respectively, and are increasing at a rate of 1% per year (1). Surgery is the most effective treatment for renal tumours. For T1 stage renal tumours, the European Association of Urology (EAU) guidelines strongly recommend partial nephrectomy (PN) as the standard treatment (2). With advancements in technology, PN can also safely remove T2 stage tumours with good prognoses (3). Minimally invasive PN, including laparoscopic PN (LPN) and robot-assisted PN (RAPN), is more widely used in clinical practice due to its lower blood loss and fewer complications compared to open PN (OPN) (4,5).

Accurately assessing surgical risk before nephron-sparing surgery (NSS) aids in the selection of treatment plans and evaluation of postoperative outcomes for patients with renal tumours. The most commonly used R.E.N.A.L. (Radius, Exophytic/Endophytic, Nearness, Anterior/Posterior, Location) nephrometry scoring system, first proposed by Kutikov et al. in 2009, includes five components: tumour location (anterior/posterior), tumour position relative to the polar lines, exophytic/endophytic properties, maximum tumour diameter, and nearness of the tumour to the collecting system or renal sinus. This scoring system is based on preoperative computed tomography (CT) or magnetic resonance imaging (MRI) examinations and quantifies the anatomical structure of the renal tumour to assess its complexity preoperatively. According to the score, renal tumours are classified into low, moderate, and high complexity (6).

Previous studies have demonstrated the ability of the R.E.N.A.L. score to predict perioperative outcomes (7-10), but these studies did not consider the impact of different surgical approaches on predictive accuracy. Since RAPN was first reported in 2004, it has been shown to significantly reduce the difficulty of tumour excision and suturing (11). A subsequent study indicated that RAPN has advantages over LPN in terms of conversion rates to open or radical surgery, warm ischaemic time (WIT), length of stay (LOS), and renal function preservation (12). However, it is unknown whether the technical advantages of RAPN affect the predictive value of the R.E.N.A.L. score. The goal of PN is to achieve the “trifecta”, which refers to a negative surgical margin, minimal loss of renal function, and the absence of major complications (13). Therefore, the purpose of this study is to explore the impact of different minimally invasive surgical methods on the predictive value of the R.E.N.A.L. score and to compare the accuracy of the R.E.N.A.L. scoring system in predicting trifecta outcomes of RAPN and LPN. Additionally, we employed another commonly used scoring system, the Simplified PADUA REnal (SPARE) nephrometry system (14), which includes rim location, renal sinus involvement, exophytic rate, and tumour dimension, to further validate our hypothesis. We present this article in accordance with the STROBE reporting checklist (available at https://tau.amegroups.com/article/view/10.21037/tau-24-534/rc).

Methods

Study design

The study was conducted in accordance with the Declaration of Helsinki (as revised in 2013). The study was approved by the Ethics Committee of the First Affiliated Hospital of Sun Yat-sen University (No. 2023703) and individual consent for this retrospective analysis was waived.

We retrospectively analyzed the data of patients with localized renal tumours who underwent RAPN or LPN at a single centre from June 2016 to June 2023. Surgeries were performed by experienced surgeons in warm ischaemic conditions. Patients with multiple tumours of the kidney, special types of kidneys such as duplicate kidneys, solitary kidneys, horseshoe kidneys, and incomplete clinical data were excluded.

Preoperative evaluation

All patients underwent preoperative CT or MRI to assess the anatomical features of the renal mass. All radiological images were analysed by a specialist urologist to determine each variable in the SPARE and R.E.N.A.L. scores for each patient, and the results obtained were reviewed by another urologist for re-examination. According to the R.E.N.A.L. score, the complexity of renal mass was classified into three levels (low complexity 4–6, medium complexity 7–9, high complexity 10–12). According to the SPARE score, the complexity of renal mass was also classified into three levels (low complexity 0–3, medium complexity 4–7, high complexity 8–10). Preoperative characteristics of the patients and tumours were collected in the electronic medical record system. Demographic data including age, gender, body mass index (BMI), and the patient’s creatinine data were collected during the preoperative week to calculate the preoperative estimated glomerular filtration rate (eGFR) using the CKD-EPI formula. Tumour characteristics include tumour size, right and left sides.

Outcomes

Perioperative variables included operative time (OT), WIT, blood transfusion rate, and estimated blood loss (EBL). Information on whether the surgical access was transperitoneal or retroperitoneal was also collected. In our study, all surgeries were performed using the on-clamp approach. Postoperative variables included LOS, time of drain removal, incidence of positive surgical margins, eGFR before discharge from hospital, calculation of the rate of change in eGFR [defined as (postoperative eGFR − preoperative eGFR)/preoperative eGFR × 100%], and complications. Postoperative complications were classified according to the Clavien-Dindo classification and distinguished as minor (grade 1–2) and major (grade >2) complications (15). We also collected postoperative tumour characteristics, including histological type and pathological staging. Achievement of trifecta was defined as the absence of Clavien-Dindo >2 complications, change in eGFR ≤10%, and no positive surgical margins.

Statistical analysis

We performed statistical calculations with SPSS version 25.0. Descriptive statistics were reported as median and interquartile range (IQR) for continuous variables and frequencies and percentages for categorical variables. Continuous variables were compared between the two groups using the Student’s t-test or non-parametric rank-sum test, while categorical variables were compared using the Chi-squared test. Spearman’s rank correlation coefficients were calculated between the R.E.N.A.L. score, the SPARE score, and quantitative perioperative outcomes. Univariate and multivariable logistic regression models adjusted with age, OT, BMI, and lesion side were used to determine the predictive value of these successive renal scores for the achievement of trifecta in two different surgical groups. Receiver operating characteristic (ROC) curve analysis was used to compare the ability of the R.E.N.A.L. and SPARE scores to predict trifecta. All tests were two-sided with a significance level at P<0.05.

Results

Patient characteristics

The demographic characteristics of the patients are summarised in Table 1. A total of 345 patients underwent RAPN. Overall, 207 (60.0%) patients were male and the median preoperative maximum tumour diameter was 32.5 [26–46.8] mm. There were 141 (50.7%) males and 137 females (49.3%) in the LPN group. The median maximal diameter of the tumour in the LPN group was 30 [23–40] mm. The difference in gender composition and preoperative diameter between the two groups was statistically significant (P=0.02 and 0.004, respectively).

Radiological score characteristics

There was a difference in the median R.E.N.A.L. score (7 vs. 6.5, P<0.001) and median SPARE score (3 vs. 2, P<0.001) between the two surgical modalities of RAPN and LPN. Table 2 details the individual characteristics of each score.

Operative and postoperative results

Among patients in the RAPN and LPN groups, the differences in WIT (20 vs. 23 min, P<0.001), EBL (50 vs. 20 mL, P<0.001), and time of drain removal (3 vs. 3 days, P=0.04) were statistically significant. In contrast, no statistical differences were observed in OT (P=0.54), postoperative complications (P=0.20), LOS (P=0.16), blood transfusion rate (P=0.62), pathological stage of tumours (P=0.18), postoperative eGFR (P=0.98), trifecta success rate (P=0.60), and the rate of change in eGFR (P=0.25). Detailed intraoperative and postoperative results are presented in Table 3.

Association between nephrometry scores and perioperative outcomes

The results of Spearman correlations of preoperative scores and postoperative outcomes in both surgical modalities are given in Table 4.

In the RAPN group, both the R.E.N.A.L. score and grade showed a strong correlation with postoperative outcomes. However, in the LPN group, R.E.N.A.L. grade was not statistically correlated with OT (P=0.07) or postoperative complications (P=0.08), and the SPARE score showed no correlation with change in eGFR (P=0.69). Additionally, SPARE grade was not correlated with change in eGFR (P=0.57) or postoperative complications (P=0.28).

Trifecta achievement

In the RAPN group, univariate analysis showed that OT (P<0.001), BMI (P=0.02), the R.E.N.A.L. score (P<0.001) and SPARE score (P<0.001) were predictors for trifecta. Multivariable analysis suggested that OT(P<0.001), the R.E.N.A.L. score (P=0.001) and SPARE score (P=0.01) were independent predictors of trifecta as reported in Table 5. As shown in Table 6, in the LPN group, both univariate and multivariable analyses identified only OT and BMI as predictors of trifecta, whereas neither the R.E.N.A.L. score nor the SPARE score were predictors. ROC curve analysis revealed the area under the ROC curves (AUCs) of 0.643 and 0.613 for the ability of the R.E.N.A.L. score and SPARE score to predict trifecta achievement in the RAPN group, respectively (Figure 1). Including WIT <20 minutes as a component of the “trifecta” is another classic definition, also referred to as margin, ischaemia, and complications (MIC) (16). Using the available data in our study, we analyzed the impact of different surgical approaches on the R.E.N.A.L. scoring system’s ability to predict MIC. As shown in Tables S1,S2, the predictive accuracy of these two scoring systems for MIC is similarly influenced by different minimally invasive surgical approaches.

Figure 1 ROC curve of the R.E.N.A.L. score used to predict trifecta achievement in the RAPN group. ROC, receiver operating characteristic; R.E.N.A.L., Radius, Exophytic/Endophytic, Nearness, Anterior/Posterior, Location; SPARE, Simplified PADUA REnal; RAPN, robot-assisted partial nephrectomy.

Discussion

To the best of our knowledge, this is the largest study to date comparing the R.E.N.A.L. score in predicting postoperative outcomes between RAPN and LPN. Since the introduction of the R.E.N.A.L. score, numerous studies have demonstrated its value in predicting surgical outcomes. Alvim et al. found that in a cohort of 304 patients undergoing open, robotic, and laparoscopic surgeries, the R.E.N.A.L. score was significantly associated with EBL, ischaemia time (IT), and the rate of change in eGFR 18 months postoperatively (17). Sugiura et al. reported that in laparoscopic surgeries, the R.E.N.A.L. score was partially correlated with OT, WIT, and eGFR, but not with EBL (18). In the study focused on robotic surgeries, Khene et al. demonstrated that the R.E.N.A.L. score was significantly associated with EBL, OT, WIT, and was a predictor of postoperative complications (19). These studies suggest that the predictive value of the R.E.N.A.L. score may vary depending on the surgical approach. Both RAPN and LPN are minimally invasive NSS that are widely used in clinical practice due to their superior renal function preservation compared to open surgery (20). This study collected clinical data from patients at a single centre who underwent LPN or RAPN, determined the R.E.N.A.L. and SPARE scores from preoperative CT or MRI images, and analyzed the correlation of these scores with postoperative outcomes to assess whether their predictive value differs between the two surgical approaches. Additionally, we compared whether the predictive value of the SPARE score is influenced by the surgical approach.

Our first finding was that in both surgical groups, the RAPN group had higher preoperative tumour diameter, median R.E.N.A.L. score, and proportion of intermediate and high-risk R.E.N.A.L. score classifications compared to the LPN group. The RAPN group also had shorter WIT, while there were no statistical differences in OT (P=0.54) and eGFR change rate (P=0.25) compared to the LPN group. These results are consistent with the previous study (21). There was no difference in the trifecta achievement rate between the two surgical groups. In this study, the postoperative drain removal time was shorter in the RAPN group than in the LPN group. The EBL in the RAPN group was higher than in the LPN group, likely due to the higher proportion of complex tumours and greater surgical difficulty in the RAPN group, leading to more intraoperative bleeding.

Our second finding is that the correlation between R.E.N.A.L. grade and postoperative outcomes differs between the two groups. In the RAPN group, both the R.E.N.A.L. score and grade showed a strong correlation with postoperative outcomes. However, in the LPN group, while the R.E.N.A.L. score correlated with postoperative outcomes, the R.E.N.A.L. grade was not correlated with some outcomes. Similarly, the correlation of the SPARE score with postoperative outcomes also demonstrated this discrepancy, further indicating that different surgical approaches can impact the assessment of postoperative outcomes by scoring systems.

Our most significant finding was that in the univariate and multivariable logistic regression models for the RAPN group, the R.E.N.A.L. score was an independent predictor for achieving trifecta, whereas in the LPN group, the R.E.N.A.L. score was not a predictor for trifecta. This preliminary result suggests that the predictive value of the R.E.N.A.L. score is influenced by the surgical method. The SPARE score also demonstrated this differential predictive value in the two surgical approaches, further confirming this observation. RAPN offers several advantages over LPN, such as a three-dimensional (3D) magnified surgical view, greater operational flexibility, and higher precision in excision and reconstruction, contributing to its increasing clinical application (22,23). These advantages of RAPN may make the R.E.N.A.L. score more accurate in predicting surgical success compared to LPN.

Previous studies on the predictive value of the R.E.N.A.L. score either did not limit the surgical approach or were confined to a single surgical method. There has been no research discussing the impact of different surgical approaches on the predictive value of the R.E.N.A.L. score. Our study is the first to confirm that the predictive accuracy of the R.E.N.A.L. score varies under different surgical approaches. In our study, the surgeons were from a single centre and were proficient in both surgical methods, which is more convincing compared to surgeons from different centres with varying levels of expertise. Among the two NSS surgical approaches, the correlation between the R.E.N.A.L. score and certain perioperative outcomes demonstrates the utility of R.E.N.A.L. as a classic scoring system. However, differences were observed in its predictive accuracy for trifecta achievement rates. Moreover, this discrepancy is not limited to the R.E.N.A.L. score; the SPARE score also showed similar variations, further emphasizing the impact of surgical approaches on the predictive accuracy of these scoring systems.

Both scoring systems determine preoperative surgical difficulty by analyzing the anatomical location of renal tumours. Previous studies have also suggested that surgical outcomes are more closely related to tumour diameter compared to the R.E.N.A.L. score (24,25). In future studies, the R.E.N.A.L. score may require modifications, such as incorporating the tumour contact surface area as a variable or adjusting the weighting of each variable, to enhance its accuracy in predicting postoperative outcomes across different minimally invasive surgical approaches. Our study has significant clinical implications. When a surgeon prepares to perform RAPN, the R.E.N.A.L. score effectively assesses tumour complexity and predicts surgical success. However, if LPN is performed, we may need a new scoring system to more accurately assess surgical difficulty and predict trifecta outcomes. This can help surgeons make more accurate decisions when selecting treatment options.

There are certain limitations in this study. First, as a retrospective study, further prospective research is needed to validate our conclusions. Second, we selected short-term postoperative outcomes, and it remains unknown whether there are differences in the predictive value of the R.E.N.A.L. score for long-term surgical outcomes, such as survival time, between the two surgical approaches. Third, although all surgeries in our study were performed by experienced surgeons, variations in surgeon experience and the differing complexity of tumours between the two groups may have influenced the outcomes. Lastly, our study focused on the commonly used clinical approaches of LPN and RAPN, and whether differences exist in other surgical methods requires further investigation.

Conclusions

The R.E.N.A.L. score is an effective tool for preoperatively assessing the complexity of renal masses. However, different surgical techniques can influence the predictive accuracy of the R.E.N.A.L. score, with it being more accurate in predicting trifecta achievement following RAPN compared to LPN.

Acknowledgments

None.

Footnote

Reporting Checklist: The authors have completed the STROBE reporting checklist. Available at https://tau.amegroups.com/article/view/10.21037/tau-24-534/rc

Data Sharing Statement: Available at https://tau.amegroups.com/article/view/10.21037/tau-24-534/dss

Peer Review File: Available at https://tau.amegroups.com/article/view/10.21037/tau-24-534/prf

Funding: None.

Conflicts of Interest: Both authors have completed the ICMJE uniform disclosure form (available at https://tau.amegroups.com/article/view/10.21037/tau-24-534/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. The study was conducted in accordance with the Declaration of Helsinki (as revised in 2013). The study was approved by the Ethics Committee of the First Affiliated Hospital of Sun Yat-sen University (No. 2023703) and individual consent for this retrospective analysis was waived.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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