Comparison of Measured Renal Tumor Size Versus R.E.N.A.L. Nephrometry Score in Predicting Patient Outcomes After Robot-Assisted Laparoscopic Partial Nephrectomy

Abstract

Partial nephrectomy (PN) is a technically challenging procedure, making selection of appropriate patients paramount to a successful operation. To identify patients at increased risk of an adverse outcome after PN, there are a number of scoring systems available. The nephrometry score was initially described in a series of laparoscopic and open partial and radical nephrectomies. We compare the association of the nephrometry score with perioperative outcomes in a population of robot-assisted partial nephrectomies. A total of 119 patients were retrospectively reviewed. Correlation and regressional analysis was performed. We identified the separate variables R, E, N, and L to have limited correlation and no predictive value to patient outcomes. Nephrometry score and grade were found to have stronger correlation and predictive value than the individual components of the R.E.N.A.L. nephrometry score. Size of tumor measured on a continuous scale was found to have the strongest correlation and predictive value to outcomes. Outcomes predicted included operative time, length of stay, warm ischemia time, and entry into the collecting system.

Introduction

Small renal masses are often identified on an incidental basis during a workup for an unrelated symptom. Radical nephrectomy and partial nephrectomy (PN) have been shown to have equivalent results as treatment options for small renal masses.¹ PN allows excision of the mass while preserving the maximum amount of renal parenchyma.

Previously published results have identified various descriptive characteristics of each tumor such as hilar location and large size as being associated with increasingly difficult resections. These resections are thought to be more prone to produce adverse perioperative outcomes and potentially long-term adverse effects such as leaks, bleeds, or cancer recurrence. Resection of a mass that might be difficult for one surgeon, however, may be routine for another surgeon of a different skill level. This has made comparisons between surgeon case series in publications difficult. Attempts to create scoring systems were made by several groups and have included the R.E.N.A.L. (radius; exophytic/endophytic; nearness; anterior/posterior; location) Nephrometry Score, preoperative aspects and dimensions used for an anatomical (PADUA) Score, and C-Index.^2
–4

Each of the nephrometry scoring systems examines a different set of variables characterizing the renal mass. The R.E.N.A.L. nephrometry and PADUA scores both analyze renal mass size, exophytic/endophytic, closeness to the collecting system, and polar location albeit in slightly different manners. The PADUA scoring system also examines the laterality of the tumor within the kidney as a factor.⁴ A number of studies have been published looking at the application of the nephrometry scores to patients undergoing PN.^{5

–17}

The previous literature is heterogeneous in the patient population that is analyzed. The approach of surgery and the number of surgeons or centers studied is different within each study. Only two studies examine robot-assisted PN. We present our experience with 119 cases of robot-assisted PN performed via the transperitoneal approach. This would be the largest series of robot-assisted PNs looking at the R.E.N.A.L. nephrometry score.

Patients and Materials

The study was approved by the Institutional Review Board. We then performed a retrospective analysis of the available records between 2007 and 2013 of patients who had undergone da Vinci assisted laparoscopic PN by a single surgeon at Indiana University. As described by Kutikov and associates,² the R.E.N.A.L. nephrometry scoring system was applied to CT scans preoperatively. Intraoperative and postoperative complications were classified according to the Clavien-Dindo system.¹⁸ Estimated glomerular filtration rate (GFR) was calculated by applying the Modification of Diet in Renal Disease formula.¹⁹

Consent was obtained, and patients were then positioned in a modified flank position. Insufflation was obtained by placement of a Veress needle in the periumbilical region. A 12-mm laparoscopic port was placed at the periumbilical region. Working trocars consisted of two additional 8-mm trocars. An additional 8-mm port was optionally placed for use of the fourth robotic arm in cases that might need additional reach. Once the kidney was mobilized, ultrasonography was used to confirm the location of the tumor. Selective clamping was performed when feasible. Resection was then performed, and the tumor bed was sampled for a frozen section to confirm negative margins. Renorrhaphy was performed, and the use of additional hemostatic agents was decided on intraoperatively based on the size of the defect and degree of hemostasis.

Data were entered into an Excel worksheet, and SPSS v20 was used for statistical analysis. Patient demographics were investigated by generating the means, ranges, and standard deviations for each characteristic. Pearson correlation was used for parametric data. Spearman correlation was used for nonparametric data. Linear regression was used to identify a relation between continuous variables and outcome variables. For nominal data, a logistic regression was performed.

Results

Patient demographics are identified in Table 1. The average size of the renal masses was 2.7 cm, which resulted in most of the patients having a R score of 1 (89%). Most tumors were exophytic in nature (51%) followed by those that were partially exophytic (38%). Only 10% of tumors treated were completely endophytic. The tumor location to the collecting system as assessed by the N score resulted in a bimodal distribution. A slight predominance of tumors was located in the posterior region (45%) vs 37% in the anterior position. The L score also resulted in a bimodal distribution. The overall nephrometry score was an average of 6.55 with a standard deviation of 1.75. Most of the tumors were thus categorized as intermediate in nephrometry grade (38%).

Table 1.

Characteristics of the Study Population

Patient demographics	Value (range or percentage)	Standard deviation
Age (years)	58.3 (18.5–79.9)	13.0
Sex	Male 65% Female 55%
Weight (kg)	92.9 (47.0–156.0)	22.0
BMI (kg/m²)	31.3 (20.2–50.8)	6.4
Renal function (mL/min/1.73 m²)	Preop GFR 76.4 (39.2–133.7)	18.2
	Postop GFR 68.8 (27.0–135.6)	20.4
Follow-up duration (months)	8.9
Nephrometry characteristics
Size of mass (cm)	2.7 (1.0–6.5)	1.1
R score
1	106 (89%)
2	12 (10%)
3	1 (0.8%)
E score
1	61 (51%)
2	45 (38%)
3	13 (10%)
N score
1	51 (43%)
2	24 (20%)
3	44 (37%)
A score
Anterior	44 (37%)
Posterior	54 (45%
X	21 (18%)
L score
1	50 (42%)
2	31 (26%)
3	38 (32%)
Nephrometry score	6.55 (4–11)	1.750
Nephrometry grade
Low (4–6)	35 (29%)
Intermediate (7–9)	45 (38%)
High (10–12)	39 (33%)
Intraoperative characteristics
OR time (minutes)	216.1 (116–363)	50.8
WIT (minutes)	19.1 (0–39)	9.1
EBL (mL)	242.1 (30–1500)	293.9
LOS (days)	2.6 (1–7)	1.0
Collecting system entry	No: 83 (70%)
	Yes: 36 (30%)
Off-clamp excision of tumor	12 (10.0%)
Intraoperative complications	5 (4.2%)
Conversions	MIS: 5 (4.2%)
	Open: 1 (0.8%)
	Radical: 2 (1.6%)
Cancer recurrence	1 (0.8%)
Postoperative complications	Clavien I: 13 (84.6%)
	Clavien II: 2 (11.1%)
	Clavien IIIa: 2 (1.7%)
	Clavien IIIb: 0 (0%)
	Clavien IVa: 1 (0.9%)
	Clavien IVb: 0 (0%)
	Clavien V: 0 (0%)
Pathology characteristics
Size (cm)	2.5 (1–5.5)	1.0
Malignant	No: 20 (16.8%)
	Yes: 99 (83.2%)
Type	Clear-cell carcinoma: 74 (75.5%)
	Papillary: 17 (17.3%)
	Chromophobe: 2 (2.0%)
	Unclassified: 5 (5.1%)
	Other: 1 (0.08%)
Fuhrman grade	Grade One: 6 (6.1%)
	Grade Two: 66 (66.7%)
	Grade Three: 27 (27.3%)
Margin invasion	No: 117 (98.3%)
	Yes: 2 (1.7%)
TNM stage	1a: 88 (90.0%)
	1b: 10 (10.2%)
	2a: 0 (0%)
	2b: 0 (0%)
	3a: 1 (1.0%)
Metastasis	No: 110 (99.1%)
	Yes: 1 (0.09%)

BMI=body mass index; preop=preoperative; GFR=glomerular filtration rate; postop=postoperative; OR=operative; WIT=warm ischemia time; EBL=estimated blood loss; LOS=length of stay; TNM=tumor, node, metastasis.

The majority of the tumors were malignant (83.2%) and of these, the most predominant was clear-cell carcinoma (75.5%). Only two tumors had margin invasion on pathologic analysis, and one tumor was observed to be metastatic to the lymph nodes (0.09%)

Table 2 presents the results of the correlation and regressional analysis. The factors R, E, N, and L were subject to Spearman correlation as well as regression. We identified a significant correlation of radius, nearness, and location to various outcome factors. The outcome factors were, however, not consistent across the independent variable. R correlated with warm ischemia time (WIT) (P=0.037). The correlation with operative (OR) time was borderline but trending toward significance (P=0.056). E was found to be neither correlated with nor predictive of any of the outcome variables examined.

Table 2.

Results of the Correlation and Regressional Analysis

Variable	Statistical analysis	Outcome examined
		OR time		Length of stay		Estimated blood loss		Warm ischemia time		Last GFR		Intraoperative complications		Collecting system entry		Last GFR to preoperative GFR		Postoperative complications
		Coefficient	P-value	Coefficient	P-value	Coefficient	P-value	Coefficient	P-value	Coefficient	P-value	Coefficient	P-value	Coefficient	P-value	Coefficient	P-value	Coefficient	P-value
R	Spearman correlation	0.18	0.056	0.09	0.307	0.08	0.409	0.19	0.037	−0.14	0.141	−0.73	0.428	0.07	0.472	−0.06	0.536	0.08	0.381
	Regressional analysis	26.35	0.063	0.32	0.248	−30.33	0.712	3.20	0.203	−6.83	0.301	−18.35	0.999	0.20	0.734	−5.32	0.351	0.83	0.294
E	Spearman correlation	0.084	0.365	0.02	0.846	0.05	0.563	−0.10	0.260	−0.03	0.766	−0.13	0.177	−0.03	0.721	−0.06	0.504	0.07	0.451
	Regressional analysis	4.05	0.586	−0.05	0.713	6.45	0.882	−2.05	0.123	−2.44	0.445	−1.62	0.170	−0.54	0.141	−2.45	0.375	0.32	0.440
N	Spearman correlation	0.14	0.124	0.14	0.141	0.18	0.054	0.11	0.254	−0.01	0.949	−0.03	0.739	0.27	0.003	0.06	0.539	0.06	0.543
	Regressional analysis	0.91	0.878	0.14	0.232	17.16	0.620	1.27	0.230	1.86	0.448	0.37	0.531	0.88	0.002	2.60	0.221	−0.01	0.973
L	Spearman correlation	0.12	0.208	0.19	0.034	0.13	0.154	0.09	0.359	−0.03	0.760	−0.02	0.816	0.04	0.699	−0.06	0.550	0.10	0.275
	Regressional analysis	5.67	0.310	0.17	0.120	48.40	0.140	0.20	0.842	−1.80	0.440	−0.13	0.819	−0.11	0.664	−1.72	0.392	0.32	0.303
Size of mass (cm)	Pearson correlation	0.31	0.001	0.26	0.002	0.08	0.208	0.31	0.001	−0.04	0.319	−0.04	0.635	0.22	0.014	−0.08	0.207	0.12	0.203
	Regressional Analysis	14.64	0.001	0.25	0.004	20.68	0.416	2.67	0.001	−0.85	0.639	−0.23	0.632	0.45	0.019	−1.30	0.415	0.24	0.274
Nephrometry score	Pearson Correlation	0.16	0.041	0.21	0.012	0.13	0.085	0.07	0.237	−0.50	0.288	−0.09	0.332	0.16	0.080	−0.05	0.309	0.05	0.596
	Regressional Analysis	4.65	0.082	0.12	0.024	21.28	0.170	0.34	0.474	−0.63	0.576	−0.27	0.336	0.20	0.082	0.49	0.618	0.20	0.186
Nephrometry grade	Pearson Correlation	0.15	0.053	0.21	0.011	0.11	0.129	0.09	0.170	−0.04	0.352	−0.06	0.502	0.18	0.049	0.01	0.461	0.05	0.589
	Regressional Analysis	9.54	0.107	0.27	0.021	38.88	0.257	1.01	0.340	−0.92	0.704	−0.34	0.503	0.51	0.051	0.21	0.922	0.36	0.266

OR=operative; GFR=glomerular filtration rate.

The only factor out of R, E, N, and L that was found to have significance during regression analysis was N. The value of N was found to have significant predictive value with the outcome of entry in the collecting system (P=0.002). This was found to be a positive correlation with a coefficient of 0.883. N was also found to have correlated with entry to the collecting system (P=0.003). N had borderline correlation with estimated blood loss (EBL) (P 0.054).

Size of mass measured as a continuous variable was identified as the most significant factor correlated to outcomes. P values were found to be very significant in the correlation to OR time (P=0.001), length of stay (LOS) (P=0.002), and WIT (P=0.001). Size of mass was also highly significant in its correlation to collecting system entry (P=0.014). Of the independent variables we analyzed, the size of the mass was seen to have the most factors correlated with it, including the four dependent variables of OR time, LOS, WIT, and collecting system entry. Size also had the most impact in terms of predictive value with significant relation to the same four variables of OR time, LOS, WIT, and collecting system entry.

The nephrometry score and grade were more predictive of outcomes than the individual components of the of R.E.N.A.L. nephrometry system. LOS and collecting system entry were correlated and predicted by nephrometry grade. Nephrometry score correlates to OR time and LOS but was also found to be predictive in LOS (P=0.024). The nephrometry grade correlates to OR time (P=0.053), LOS (P=0.011), and collecting system entry (P=0.049) but only predicts outcomes in LOS and collecting system entry.

Intraoperative complications in our series included two conversions to open surgery for bleeding. The other three intraoperative complications included an inferior vena cava bleed, renal vein bleeding, and a splenic laceration/bleeding.

Discussion

Since the original nephrometry score was described in 2009, there have been a total of 13 articles in the literature that have attempted to correlate the scores of nephrometry, C-index, or PADUA score to surgical outcomes (Table 3). All the articles are retrospective chart reviews and therefore of level 5 US Preventive Services Task Force quality of evidence. Dependent factors found to be predicted by the scoring systems have included overall complication rate, WIT, OR time, EBL, LOS, and GFR. One author found that the scoring system did not correlate with operative outcomes.¹⁰

Table 3.

Summary of Previous Nephrometry Publications

Author	Year published	Systems analyzed	Number of patients	Number of surgeons	Technique	Surgical approach	Dependent variables	Associated outcomes
Kutikov and Guzzo²	2009	R.E.N.A.L. Nephrometry	50	?	Open, Laparoscopic, Robotic		n/a	n/a
Ficarra et al.⁴	2009	PADUA	164	3	Open	Flank (extraperitoneal)	PADUA score	Overall complication rate
Simmons et al.³	2010	C-index	133	1	Laparoscopic	Trans	C-index	WIT
Tsivian et al.⁵	2012	R.E.N.A.L. Nephrometry/PADUA	147	1	Laparoscopic	Transperitoneal	Tumor size, Centrality, Endophytic growth	WIT, OR time
Minervini et al.⁶	2013	PADUA	244	?	Open	Retroperitoneal (flank)	PADUA score, endophytic growth, diameter, involvement of collecting system/sinus	WIT, complications
Ellison et al.⁷	2013	R.E.N.A.L. Nephrometry	298	8	Mixture: (HAPN, LPN, RAPN)	Mixture: Trans/Retro	Nephrometry score, distance to renal sinus	WIT, EBL, OR time, LOS, complications
Samplaski et al.⁸	2010	C-index	131	1	Laparoscopic	Transperitoneal	C-index	GFR
Hew et al.⁹	2011	R.E.N.A.L. Nephrometry/PADUA	134	3 centers	Not stated		Highest categories of PADUA and Nephrometry	WIT, Complications
Mafarrij et al.¹⁰	2011	R.E.N.A.L. Nephrometry	92	1	Robotic	Transperitoneal	No associations	None
Long et al.¹¹	2013	R.E.N.A.L. Nephrometry	177	4	Mixture: open (159) and lap (18)	Extraperitoneal (open) and intraperitoneal (laparoscopic)	Nephrometry score	WIT, Conversion to radical nephrectomy
Mayer et al.¹²	2012	R.E.N.A.L. Nephrometry	67	1	Laparoscopic (12) and robotic (55)	Transperitoneal	Nephrometry score, R score, N score	WIT, Collecting system entry
Tyritzis et al.¹³	2011	PADUA	74	?			PADUA	Complications
Kruck et al.¹⁴	2012	R.E.N.A.L. Nephrometry/PADUA	81	1	Laparoscopic	Transperitoneal	Tumor centrality, tumor size	OR time, EBL, GFR
Simhan et al.¹⁵	2011	R.E.N.A.L. Nephrometry	390	?	Mixture: open (216), robot (174)		Nephrometry score	Major complications
Okhunov et al.¹⁶	2011	R.E.N.A.L. Nephrometry/PADUA/C-index	101	?	Laparoscopic	Transperitoneal	Nephrometry/PADUA/C-index	WIT, GFR and tumor size, LOS (C-index only)
Png et al.¹⁷	2013	R.E.N.A.L. Nephrometry	83	1	Robotic	Transperitoneal	Nephrometry	WIT

R.E.N.A.L.=radius; exophytic/endophytic; nearness; anterior/posterior; location; PADUA=preoperative aspects and dimensions used for an anatomical; n/a=not applicable; WIT=warm ischemia time; OR=operative; EBL=estimated blood loss; GFR=glomerular filtration rate; LOS=length of stay.

The R.E.NA.L. nephrometry score was created based on literature review of salient characteristics of renal tumors that were previously found to have an effect on operative outcomes. Radius was identified as the most consistent and reproducible factor in the past. Other characteristics, however, were also deemed important to convey. The exophytic and endophytic nature of the tumor was scored on an easy to use system of above or below 50%. Nearness to the collecting system was scored on a three-point score that was assigned arbitrarily.

Recent literature has aimed to correlate the scores with the outcomes of surgery. In a robotic series, Mufarrij and colleagues¹⁰ found that no variables were associated with any of the outcomes they analyzed. Png and coworkers¹⁷ found that the nephrometry score correlated with the WIT. The number of patients was similar between studies with 92 and 83 in the series. In contrast to the other publications on nephrometry scoring, the use of nephrometry in the robotic series seemed to be less predictive of outcomes.

Conclusion

Our results support what has been identified in previous articles looking at the application of the nephrometry score to patient populations undergoing PN. First, the components of the nephrometry score do not have predictive ability for operative outcomes. Second, the total nephrometry score and the nephrometry grade were identified have some correlation to outcomes. Finally, we conclude that size does indeed matter. More specifically, the size of the tumor on a continuous scale was seen to be the strongest predictor of outcomes.

We note an interesting trend in that converting from a linear measure of size to the R scale we lose most or all of the correlation/predictive ability of the variable to the outcomes. We hypothesize that there may be more appropriate division of the categories of R that may conserve this predictive quality of size toward the outcomes. The variables E, N, and L also require conversion from a measured continuous variable into a categoric value. These factors may also have more significant predictive value kept on a continuous linear scale.

Weaknesses of this study include the retrospective nature of the review. The study is applicable to robot-assisted PNs but may not be applicable to a pure laparoscopic approach or the open approach. Although our study has the largest population of patients studied for robot-assisted PN, the patient population is still limited at n=119. In addition, the majority (89%) of the tumors managed in this cohort were predominantly within the lowest category of R (below 4 cm in diameter).

The measures in the R.E.N.A.L. scale were generated arbitrarily in the original score and may benefit from different cutoff values for each of their categories. This may improve the ability of the scoring system to correlate/predict outcomes of robot-assisted PN.

Disclosure Statement

No competing financial interests exist.

Footnotes

Abbreviations Used

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