New Longitudinal Component of the RENAL Nephrometry Score for Predicting the Operative Complexity in Transperitoneal Robot-Assisted Partial Nephrectomy

Abstract

Background:

In transperitoneal robot-assisted partial nephrectomy (RAPN), an L score of 3 points according to the RENAL nephrometry scoring system does not necessarily denote operative complexity. This study aimed to assess the efficacy of the newly defined longitudinal component to analyze the operative complexity of RAPN.

Materials and Methods:

We retrospectively analyzed transperitoneal RAPNs performed by a single experienced surgeon for renal tumors between 2017 and 2020. L component was defined as L′1 for midlocated tumors, L′2 for >50% below the polar line, and L′3 for >50% above the polar line. Multivariate regression analysis was performed to test associations between prolonged console time and preoperative factors. The perioperative outcomes were compared among the three cohorts of L′ components using propensity score matching: L′1 vs L′3 and L′1 vs L′2.

Results:

A total of 220 cases (L′1: 107, L′2: 65, L′3: 48) were analyzed. The median console time was prolonged (>130 minutes) in 55 patients (median 108, interquartile range: 90–130 minutes). Longitudinal location (L′3 odds ratio [OR]: 2.93, p = 0.01; L′2 OR: 2.32, p = 0.04), high Mayo adhesive probability score (p = 0.001), multiple renal arteries (p = 0.03), and large size (p = 0.04) were significantly associated with prolonged console time. After matching, 26 cases of L′1 and L′3 and 43 cases of L′1 and L′2 were selected. Console time (108 minutes vs 132 minutes, p = 0.017) and warm ischemia time (17 minutes vs 22 minutes, p = 0.03) were significantly longer in L′3 than in L′1. The difference in console time between L′1 and L′2 was not statistically significant (100 minutes vs 111 minutes, p = 0.08).

Conclusion:

In the new longitudinal assessment, upper location predicted prolonged console time compared with a middle or lower location. The L′ component may help preoperatively assess operative complexity.

Introduction

With the prevalence of minimally invasive surgery (MIS), robot-assisted partial nephrectomy (RAPN) has been widely used for the treatment of small renal masses.^1
–3 The RENAL nephrometry and preoperative aspects and dimensions used for an anatomical score are one of the well-known classification systems of anatomical tumor position for predicting perioperative outcomes, including complication rate, ischemia time, and trifecta achievement in partial nephrectomy.^4

–7 Based on their specific components, these systems classify renal tumors into three categories—low, moderate, and high complexity. Particularly, one of the components in the RENAL nephrometry scoring system is longitudinal position (L), which distinguishes between a lateral or position.

In our clinical experience of transperitoneal RAPN, midlocated small renal tumors (L3) are not necessarily difficult to manage. Meanwhile, surgeons often face difficulty dissecting around the kidney and tumor resection for upper located tumors (L1) due to the need for wide dissection around the Gerota's fascia and kidney rotation for tumor recognition.^8,9 Similarly, lower located tumors require time and skill to dissect from the ureter and rotate the kidney. Therefore, we defined a new longitudinal component (L′ component) by classifying tumors as middle, lower, or upper located. This study aimed to evaluate the predictive ability of the newly defined longitudinal tumor classification for operative complexity by comparing perioperative outcomes, including operative times, complication rate, and renal function.

Materials and Methods

Study population

Institutional Review Board approval was obtained from Tokyo Women's Medical University for the retrospective analysis of patient data (5767). A total of 220 patients who underwent transperitoneal RAPN for renal tumors at a single high-volume institution between March 2017 and December 2020 were retrospectively analyzed. Clinical and pathologic parameters of each patient were obtained from electronic medical charts. All patients underwent enhanced CT or MRI before surgery, and three-dimensional images of renal vessels and renal tumors were obtained for determining the surgical approach. Surgery was performed with the da Vinci X surgical system (Intuitive Surgical, Sunnyvale, CA) by one experienced surgeon (T.K.) whose case volume surpasses more than 600 cases.

Furthermore, this study included RAPNs later than the 100th case, with consideration for the impact of the learning curve.^10
–12 Tumors were excised under warm ischemia with standard parenchymal margin or tumor enucleation, based on the tumor complexity and surgeon's preference, and early unclamping was adopted to decrease ischemic time.^3,13 For each case, the RENAL nephrometry score was used to describe anatomical renal tumor position.⁵

The Mayo adhesive probability (MAP) score, which was developed for predicting the difficulty of nephron sparing surgery, was also calculated from preoperative enhanced CT or MRI by a urologist (H.T.) not involved in these surgeries. Specifically, the MAP score consists of the perinephric fat stranding extent and thickness and reflects surgical difficulty while dissecting the perinephric fat around the tumor. Both scores were summed up from 0 to 5.¹⁴

Preoperative and postoperative global renal functions were assessed using the estimated glomerular filtration rate (eGFR) before surgery, during postoperative nadir, and at 1 and 3 months after surgery. The eGFR was calculated using the Modification of Diet in Renal Disease 2 equation modified for Japanese patients, as outlined by the Japanese Society of Nephrology (eGFR = 1.94 × serum creatinine mg/dL^1.094 × age × 0.739 [if female]).¹⁵ Postoperative complication was classified using the Clavien–Dindo classification system.¹⁶

Tumor assessment

In addition to the RENAL nephrometry score, we defined the new L′ component, consisting of the longitudinal positions of the renal tumor (L′1: midportion, L′2: lower portion, and L′3: upper portion). Specifically, L′1 is indicated when the tumor crosses the axial renal midline, entirely between polar lines, or >50% across the polar line at the same level of L3. Meanwhile, L′2 is indicated when the tumor is entirely below the polar line or <50% across the lower polar line, whereas L′3 is indicated when the tumor is entirely above the polar line or <50% across the upper polar line (Fig. 1).

FIG. 1.

The newly proposed longitudinal assessment (L′) of renal tumors. L′1 crosses the axial renal midline, entirely between polar lines, or >50% across the polar line. L′2 is entirely below the polar line or <50% across the lower polar line. L′3 is entirely above the polar line or <50% across the upper polar line. Color images are available online.

Statistical analyses

Multivariate regression analysis was used to assess the association between prolonged console time and potential preoperative factors (age, sex, MAP score, body mass index [BMI], anticoagulant use, history of abdominal surgery, RENAL score tumor laterality, and the newly defined L′ component). Prolonged console time was defined when the console time exceeded the upper interquartile point.

To compare perioperative outcomes and minimize selection bias between the two groups (L′1 vs L′3, and L′1 vs L′2), patient variables, including age, sex, BMI, tumor laterality, number of renal arteries, MAP score, history of abdominal surgery, tumor size, and RENAL score except the L component, were all adjusted using 1:1 propensity score matching. Propensity scores were then calculated using a multivariate regression model, with a caliper width of one-fifth of 1 standard deviation of the logit.¹⁷ All statistical analyses were calculated with the JMP Pro 15 (SAS Institute, Cary, NC) software, and a p-value <0.05 was considered statistically significant. Student's t-test, χ² test, and Mann–Whitney U test were used for continuous, unordered categorical, and ordinal categorical variables, respectively.

Results

Patient and tumor background

Characteristics of the 220 patients (L′1: 107, L′2: 65, and L′3: 48) before matching are listed in Table 1. Exactly 152 (69%) out of the 220 patients were male. The mean age was 58 years, and the mean BMI was 24.5 kg/m². Only 72 patients (32.7%) had a history of abdominal surgery. The RENAL nephrometry score showed high, intermediate, and low complexity in 30 (13%), 137 (63%), and 53 (24%) cases, respectively. The MAP scores were 0, 1, 2, 3, 4, and 5 in 107 (49%), 27 (12%), 32 (15%), 16 (7%), 34 (15%), and 4 (2%) cases, respectively.

Table 1.

Patient and Tumor Characteristics According to the L′1 Component

	L′ 1 (N = 107)	L′2 (N = 65)	L′3 (N = 48)	p
Age, years	56 ± 13	58 ± 14	63 ± 10	0.01
Male, n	77 (71.9)	41 (63.0)	34 (70.8)	0.45
Body mass index, kg/m²	24.2 ± 3.9	24.8 ± 5.7	24.7 ± 4.1	0.68
ECOG PS (0/1)	105 (99.1)/1 (0.9)	64 (98.5)/1 (1.5)	46 (95.8)/2 (4.2)	0.43
ASA score (1/2/3)	44 (41.1)/61 (57.0)/2 (1.9)	21 (32.3)/40 (61.5)/4 (6.2)	13 (27.1)/34 (70.8)/1 (2.1)	0.24
History of abdominal surgery, n (%)	32 (30)	21 (32.3)	19 (39.5)	0.49
Presence of HT (%)	42 (39.2)	31 (47.7)	24 (50.0)	0.36
Presence of DM (%)	17 (15.9)	15 (23.1)	9 (18.7)	0.5
Tumor laterality, left, n (%)	52 (48.6%)	31 (47.7%)	26 (54.2%)	0.76
Tumor size, cm	2.7 ± 1.4	3.1 ± 1.4	3.7 ± 1.8	0.0012
RENAL score
Low, n (%)	11 (10.3)	22 (33.9)	20 (41.7)
Intermediate, n (%)	66 (61.7)	43 (66.1)	28 (58.3)	<0.0001
High, n (%)	30 (28)	0	0
R (1/2/3)	91 (85.1)/16 (14.9)/0	48 (73.8)/17 (26.2)/0	27 (56.3)/21 (43.7)/0	0.0006
E (1/2/3)	16 (14.9)/69 (64.5)/22 (20.6)	17 (26.1)/41 (63.1)/7 (10.8)	11 (22.9)/32 (66.7)/5 (10.4)	0.16
N (1/2/3)	30 (28.0)/8 (7.5)/69 (64.5)	19 (29.2)/9 (13.9)/37 (56.9)	18 (37.5)/3 (6.3)/27 (56.3)	0.44
A (a/x)	62 (57.9)/45 (42.1)	20 (30.8)/45 (69.2)	11 (22.9)/37 (77.1)	<0.0001
L (1/2/3)	0/0/107 (100)	31 (47.7)/34 (52.3)/0	26 (54.2)/22 (45.8)/0	<0.0001
h	23 (21.5)	2 (3.1)	3 (6.3)	0.0003
No. of renal arteries (1/2/3/4)	80 (74.8)/22 (20.6)/5 (4.7)/0	50 (77)/14 (21.5)/1 (1.5)	35 (72.9)/12 (25)/0/1 (2.1)	0.26
MAP score 0/1/2/3/4/5	60 (56.1)/15 (14.0)/13 (12.1)/5 (4.7)/12 (11.2)/2 (1.9)	30 (46.2)/10 (15.4)/11 (16.9)/4 (6.2)/9 (13.8)/1 (1.5)	17 (35.4)/2 (4.2)/8 (16.7)/7 (14.6)/13 (27.1)/1 (2.1)	0.07

Data are presented as average ± standard deviation or number (%).

ASA = American society of anesthesiologists; DM = diabetes mellitus; ECOG = Eastern Cooperative Oncology Group; HT = hypertension; MAP = Mayo adhesive probability; PS = performance status.

Perinephric fat thickness was <1.0 cm in 115 (52%), 1–2 cm in 45 (20%), and ≥2 cm in 60 (27%) cases. Perinephric fat stranding was unrecognized in 157 (71%) cases, whereas 57 (26%) had mild or moderate perinephric fat stranding, and 5 (2%) had severe perinephric fat stranding. The number of renal arteries was 1, 2, 3, and 4 in 165 (75%), 48 (22%), 6 (3%), and 1 (0.5%) case, respectively. On comparing the three groups according to the L′ component, L′3 (upper) cases had a higher age (p = 0.01) and larger tumor size (p = 0.001) compared with L′1 (middle) or L′2 (lower) cases. The rate of hilar tumor touching the renal artery or vein was higher in L′1 (middle) cases compared with L′2 (lower) or L′3 (upper) cases (p = 0.0003) (Table 1).

Analysis of factors influencing prolonged console time

Since the median console time was 108 minutes (interquartile range, 90–130 minutes), we defined prolonged console time as >130 minutes. Univariate analysis for predicting prolonged console time showed correlation in left-sided laterality (p = 0.03), an MAP score ≥3 (p < 0.0001), R component (p = 0.0026), L component (p = 0.009), and L′ component (p = 0.0001). Furthermore, an MAP score ≥3 (0.001), R component (p = 0.04), L′ component (p = 0.01), and a renal artery number ≥2 (p = 0.03) remained as predictive factors for prolonged console time in multivariate analysis.

Age and BMI were not included in the multivariate analysis due to concerns for possible confounding with MAP score.^10,18 The odds ratio (OR) for L′1 was 2.93 (95% confidence interval [CI] 1.19–7.24) in L′3 and 2.32 (95% CI 1.01–5.32) in L′2. As an aggregate scoring system, the RENAL score did not exhibit significant correlation with prolonged console time. Meanwhile, RENAL score showed a significant correlation with prolonged console time in univariate and multivariate analyses (OR 1.45, 95% CI 1.14–1.84) (Table 2).

Table 2.

Predictive Factors Associated with Prolonged Console Time of ≥130 Minutes in the Univariate and Multivariate Analyses

		Univariate			Multivariate			Multivariate			Multivariate
		OR	95% CI	p	OR	95% CI	p	OR	95% CI	p	OR	95% CI	p
Age (years)		1.01	0.99–1.04	0.06
Sex (male/female)		1.26	0.64–2.48	0.5
Body mass index		1.06	0.99–1.13	0.07
Antithrombotic agent use (yes/no)		1.73	0.55–5.41	0.34
History of abdominal surgery (yes/no)		0.79	0.41–1.55	0.5
Tumor laterality (left/right)		1.94	1.04–3.62	0.03	1.55	0.77–3.14	0.21	1.48	0.73–3.00	0.24	1.59	0.79–3.18	0.18
No. of renal arteries (≥2/1)		1.89	0.97–3.68	0.06	2.31	1.07–4.96	0.03	2.41	1.12–5.21	0.02	2.13	1.01–4.51	0.04
MAP score (3–5/0–2)		4.38	2.25–8.55	<0.0001	3.29	1.58–6.87	0.001	3.6	1.72–7.53	0.0007	3.86	1.88–8.93	0.0002
RENAL score
R	2	2.77	1.42–5.37	0.0026	2.16	1.02–4.58	0.04	2.05	0.96–4.38	0.06
R	1	Reference	—	—	Reference	—	—	Reference	—	—
E	3	0.92	0.35–2.39	0.87
	2	0.49	0.23–1.04	0.06
	1	Reference	—	—
N	3	1.48	0.72–3.04	0.28
	2	2.23	0.74–6.72	0.15
	1	Reference	—	—
A (anterior/X)		0.52	0.27–1.00	0.05	0.86	0.41–1.81	0.7	0.81	0.38–1.71	0.58	0.64	0.31–1.29	0.21
L	3	0.35	0.16–0.77	0.009				0.49	0.20–1.21	0.12
	2	1.4	0.64–3.04	0.39				1.57	0.64–3.85	0.32
	1	Reference	—	—				Reference	—	—
L′	3	4.77	2.16–10.5	0.0001	2.93	1.19–7.24	0.01
	2	2.53	1.18–5.43	0.017	2.32	1.01–5.32	0.04
	1	Reference	—	—	reference	—	—
h (yes/no)		1.23	0.51–2.98	0.64
RENAL score	4–12	0.97^a	0.81–1.16	0.78
RENAL′ score	4–12	1.45^a	1.16–1.81	0.0005							1.45^a	1.14–1.84	0.0012

OR ratio for a 1-unit increase.

CI = confidence interval; OR = odds ratio.

Matched cohort analysis (L′1 vs L′3)

Among the L′ 1 (N = 107) and L′ 3 (N = 48) patients, 26 patients in each group were selected (Table 3), and patient and tumor backgrounds were adjusted after matching. In these cohorts, the mean age was 62 years, and the mean tumor size was 3.2 cm. The MAP score was ≤2 in 31 (60%) and >2 in 21 (40%) patients. Tumor laterality was left in 27 (52%) patients. The RENAL score was high, intermediate, and low in 6 (11%), 31 (60%), and 15 (29%) patients, respectively. Regarding perioperative outcomes, the L′3 cohort had a longer console time (132 minutes vs 108 minutes, p = 0.017), operative time (186 minutes vs 162 minutes, p = 0.025), and ischemia time (22 minutes vs 17 minutes, p = 0.03) compared with the L′1 cohort.

Table 3.

Patient and Tumor Characteristics After Propensity Score Matching

	L′1 (N = 43)	L′2 (N = 43)	p	L′1 (N = 26)	L′3 (N = 26)	p
Age, years	56 ± 15	59 ± 15	0.37	63 ± 14	61 ± 11	0.64
Male, n (%)	15 (34.9)	15 (34.9)	1.00	21 (80.7)	19 (73.1)	0.74
Body mass index, kg/m²	25.5 ± 4.4	24.8 ± 5.9	0.58	24.5 ± 3.3	24.9 ± 4.4	0.69
ECOG PS (0/1)	43 (100)/0	43 (100)/0	—	26 (100)/0	24 (92.3)/2 (7.7)	0.49
ASA score (1/2/3)	17 (39.5)/24 (55.8)/2 (4.7)	13 (30.2)/27 (62.8)/3 (7.0)	0.63	5 (19.2)/21 (80.8)/0	7 (26.9)/18 (69.2)/1 (3.9)	0.45
History of abdominal surgery	12 (27.9)	15 (34.9)	0.64	13 (50)	11 (42.3)	0.78
Presence of HT (%)	20 (46.5)	20 (46.5)	1.00	16 (61.5)	13 (50)	0.57
Presence of DM (%)	9 (20.9)	14 (32.6)	0.33	6 (23.1)	6 (23.1)	1.00
Tumor laterality, left, n (%)	21 (48.8)	19 (44.2)	0.82	13 (50)	12 (46.2)	1.00
Tumor size, cm	3.2 ± 1.5	2.9 ± 1.4	0.37	3.2 ± 1.9	3.3 ± 1.7	0.82
RENAL score
R (1/2)	33 (76.7)/10 (23.3)	32 (74.4)/11 (25.6)	1.00	19 (73.1)/7 (26.9)	17 (65.4)/9 (34.6)	0.76
E (1/2/3)	6 (14.0)/33 (76.7)/4 (9.3)	12 (27.9)/27 (62.8)/4 (9.3)	0.27	7 (26.9)/16 (61.5)/3 (11.5)	6 (23.1)/17 (65.4)/3 (11.5)	0.94
N (1/2/3)	10 (23.3)/7 (16.3)/26 (60.5)	14 (32.6)/3 (7.0)/26 (60.5)	0.32	8 (30.8)/2 (7.7)/16 (61.5)	9 (34.6)/1 (3.9)/16 (61.5)	0.82
A (a/x)	13 (30.2)/30 (69.8)	16 (37.2)/27 (62.8)	0.64	11 (42.3)/15 (57.7)	9 (34.6)/17 (65.4)	0.77
h	6 (14.0)	2 (4.7)	0.26	8 (30.8)	3 (11.5)	0.17
No. of renal arteries (1/2/3)	36 (83.7)/6 (14.0)/1 (2.3)	31 (72.1)/11 (25.6)/1 (2.3)	0.39	23 (88.5)/3 (11.5)/0	22 (84.6)/4 (15.4)/0	1.00
MAP score (0/1/2/3/4/5)	22 (51.2)/5 (11.6)/6 (14.0)/1 (2.3)/7 (16.3)/2 (4.7)	22 (51.2)/8 (18.6)/7 (16.3)/0/6 (14.0)/2 (2.3)	0.57	12 (46.1)/0/4 (15.4)/3 (11.5)/6 (23.1)/(3.9)	10 (38.5)/2 (7.7)/3 (11.5)/1 (3.9)/9 (34.6)/1 (3.9)	0.56

Data are presented as average ± standard deviation or number (%).

Estimated blood loss and length of hospital stay did not differ significantly. Furthermore, positive surgical margin rate, complication rate, and renal functional outcome were similar between the two cohorts (Table 4).

Table 4.

Comparison of Perioperative Outcomes Among the L′ Components

	L′1 (N = 43)	L′2 (N = 43)	p	L′1 (N = 26)	L′3 (N = 26)	p
Console time, minutes	100 ± 29	111 ± 27	0.08	108 ± 33	132 ± 36	0.017
Operative time, minutes	150 ± 34	153 ± 29	0.55	162 ± 37	186 ± 39	0.025
Warm ischemia time, minutes	17 ± 8	17 ± 8	0.95	17 ± 8	22 ± 10	0.03
Estimated blood loss, mL	64 ± 87	54 ± 84	0.6	72 ± 124	54 ± 70	0.53
Length of hospital stay, days	4.9 ± 1.7	4.7 ± 2.1	0.51	4.9 ± 1.7	4.6 ± 1.0	0.49
Positive surgical margin, n	0	1 (2.3)	-	2 (7.7)	0	0.49
%decrease in eGFR
1 month	−8 ± 13	−8.1 ± 12	0.86	−4 ± 13	−5 ± 10	0.47
3 months	−0 ± 0.1	−0 ± 0.1	0.95	−0 ± 0.1	−0 ± 0.1	0.81
Complication, n (%)
Clavien grade
Any	5 (11.6)	6 (14.0)	0.74	5 (19.2)	1 (3.8)	0.19
Three or higher	1 (2.3)	0	1.00	2 (7.7)	0	0.49

Data are presented as average ± standard deviation or number (%).

eGFR = estimated glomerular filtration rate.

Matched cohort analysis (L′1 vs L′2)

Among the L′ 1 (N = 107) and L′ 2 (N = 65) patients, 43 patients in each group were selected (Table 3), and patient and tumor backgrounds were adjusted after matching. In these cohorts, the mean age was 58 years, and the mean tumor size was 3.0 cm. The MAP score was ≤2 in 70 (81%) and >2 in 16 (19%) patients. Tumor laterality was left in 40 (47%) patients. The RENAL score was high, intermediate, and low in 10 (12%), 58 (67%), and 18 (21%) patients, respectively. Regarding perioperative outcomes, console time (111 minutes vs 100 minutes, p = 0.08) tended to be longer in the L′2 cohort compared with the L′1 cohort.

Meanwhile, operative time (153 minutes vs 150 minutes, p = 0.55) and ischemia time (17 minutes vs 17 minutes, p = 0.95) did not differ significantly. Estimated blood loss and length of hospital stay were also similar. Furthermore, positive surgical margin rate, complication rate, and renal functional outcome were similar between the two cohorts (Table 4).

Discussion

In the era of MIS, RAPN has been standardized for the surgical treatment of small renal tumors. Tumor complexity is quantified by the RENAL nephrometry score, classifying tumors as high, intermediate, or low complexity.⁵ This score is used for the preoperative evaluation of the anatomical tumor position and surgery difficulty to determine perioperative complication rate, oncologic outcome, and renal functional outcome.¹⁹

In this study, we developed the L′ component, a modified version of the L component, for the evaluation of the longitudinal tumor position, showing that the L′ component was significantly associated with console time. On analysis, upper located tumors required longer operative times compared with middle or lower tumors, which was consistent with our clinical experience.

In multivariate analysis, tumor size, number of renal arteries, L′ component, and MAP score showed significant association with prolonged operative time, and an especially strong association was recognized in an MAP score ≥3. The MAP score was first developed by Davidiuk et al. in 2014, which consists of perinephric fat thickness and stranding.¹⁴ We also previously reported that an MAP score ≥3 was significantly associated with operative time prolongation, especially in the dissection phase.¹⁰ Therefore, we included the MAP score in the present analysis.

Perinephric fat thickness and stranding have been reportedly associated with the presence of adherent perinephric fat, and such patients were likely to be elderly, male, or to have high BMI, history of smoking, and cardiovascular disease.¹⁰ Khene et al. analyzed the predictive ability of the MAP score for perioperative outcomes, reporting that it was correlated with operative time, estimated blood loss, and conversion to radical nephrectomy or open surgery in RAPN; however, they did not affect the complication rate.²⁰ A possible reason for this is that major perioperative complications, including bleeding and urine leak, may be associated with the tumor resection phase.

The present analysis focused on the new longitudinal classification model as a predictive marker for surgical difficulty. Multivariate analysis showed significant console time prolongation in upper located tumors. After adjusting the background characteristics, console, ischemia, and operative times were longer in the upper located tumors than in the midlocated tumors, which was consistent with our surgical experience. During transperitoneal RAPN for anterior, middle, small renal tumors, surgeons can easily recognize the target tumor in front of the surgical field. Therefore, dissection around the tumor capsule can be minimal, and tumor resection can be performed without difficulty.

Meanwhile, upper located tumors require wide dissection of Gerota's fascia to rotate the tumor capsule in front of the surgical field. Furthermore, forceps handling tends to be limited due to the range of motion (ROM) in the da Vinci surgical system.

Among the several nephrometry scoring systems developed since 2009, the first-generation RENAL and preoperative aspects and dimensions used for an anatomical (PADUA) scores have been mainly used for objectifying the anatomical complexity of a renal tumor decision-making for nephron sparing surgery, and predicting perioperative outcomes.^21,22

Ficarra et al. also introduced the Simplified PADUA RENAL (SPARE) scoring system, in which two components—longitudinal location and urinary collecting system involvement—were excluded from the PADUA score. Although the longitudinal location was removed due to univariate analysis, the predictive ability for complication in the SPARE score was similar to the original PADUA score.²³ Moreover, Cacciamani et al. performed a meta-analysis on the association between perioperative outcomes and tumor complexity using the RENAL score in RAPN, reporting that complex tumors (RENAL ≥7) had a longer operative time, more estimated blood loss, longer warm ischemia time, and more complications compared with noncomplex tumors (RENAL <7). Larger or hilar tumors were especially associated with various perioperative outcomes.²⁴

Currently, a longitudinal classification, which only distinguishes between middle or polar locations, may be insufficient to predict perioperative outcomes. Thus, in the present study, we divided polar located tumors into the upper and lower locations. To simplify this classification, we defined L′1 as L3, L′2 as lower, and L′3 as upper, consequently showing the significant differences in operative time and ischemia time between upper and midlocated tumors.

In the comparison between the L′1 and L′3 cohorts after matching, significant differences were observed in operative time and warm ischemia time, whereas no differences in complication rate and oncologic and renal functional outcomes were found. These differences may be affected by the need for wide dissection around the kidney and the limited ROM during tumor resection for upper tumors. However, this difference indicates that only upper tumors require additional operative time, excluding surgical difficulty affecting trifecta achievement if performed by an expert surgeon. Furthermore, the benefit of L′ component classification may be inadequate to replace the RENAL nephrometry scoring system.

Meanwhile, significant differences in the operative time were not observed between L′1 and L′2 through propensity score-matched analysis. This may be due to the decreased number of cases in the matching process and the lower percentage of males and MAP scores after matching. In addition, ROM limitation in the forceps handling of lower tumors may be minimal compared with that of upper tumors.

This study has several limitations, including its retrospective nature, the collection of data from a single high-volume academic institution, and the study population's composition of tertiary care patients. The number of cases was reduced through propensity score matching because the cases that deviated from the common background in each cohort were excluded from the matched cohort analysis. Therefore, the main outcome is that the multivariate analysis and the propensity score matching results are supplementary. Furthermore, the learning curve of the surgeon may have affected perioperative outcomes, although we excluded the first 100 RAPN cases and did not change the surgical procedure throughout the study period.¹⁰

The present study excluded posteriorly located tumors, since the retroperitoneal approach has often been adopted for posterior tumors due to early access to the renal hilum and tumor. From our clinical experience, upper tumors were more difficult and time-consuming compared with midtumors due to the similar reason of the transperitoneal approach. Therefore, our new longitudinal classification may be applicable for retroperitoneal RAPN; however, further analysis will be necessary. The advantage of this study is that we showed the predictive ability of the new longitudinal classification (L′ component), which is associated with prolonged operative time.

Conclusion

We proposed a new longitudinal component in the RENAL nephrotomy scoring system, showing that the operative time was longer in upper tumors, compared with middle or lower tumors. This new L′ component will have a complementary benefit with the RENAL nephrometry scoring system in predicting the difficulty of RAPN.

Footnotes

Author Disclosure Statement

No competing financial interests exist.

Funding Information

No funding was received for this article.

Abbreviations Used

References

Haseebuddin

, Benway

, Cabello

, Bhayani

. Robot-assisted partial nephrectomy: Evaluation of learning curve for an experienced renal surgeon. J Endourol, 2010; 24:57–61.

Ghali

, Elbakry

, Hamilton

, et al. Robotic partial nephrectomy for clinical T2a renal mass is associated with improved trifecta outcome compared to open partial nephrectomy: A single surgeon comparative analysis. World J Urol, 2020; 38:1113–1122.

Tachibana

, Takagi

, Kondo

, Ishida

, Tanabe

. Robot-assisted laparoscopic partial nephrectomy versus laparoscopic partial nephrectomy: A propensity score-matched comparative analysis of surgical outcomes and preserved renal parenchymal volume. Int J Urol, 2018; 25:359–364.

Ficarra

, Novara

, Secco

, et al. Preoperative aspects and dimensions used for an anatomical (PADUA) classification of renal tumours in patients who are candidates for nephron-sparing surgery. Eur Urol, 2009; 56:786–793.

Kutikov

, Uzzo

. The R.E.N.A.L. nephrometry score: A comprehensive standardized system for quantitating renal tumor size, location and depth. J Urol, 2009; 182:844–853.

Simhan

, Smaldone

, Tsai

, et al. Objective measures of renal mass anatomic complexity predict rates of major complications following partial nephrectomy. Eur Urol, 2011; 60:724–730.

Stroup

, Palazzi

, Kopp

, et al. RENAL nephrometry score is associated with operative approach for partial nephrectomy and urine leak. Urology, 2012; 80:151–156.

Kaouk

, Khalifeh

, Hillyer

, et al. Robot-assisted laparoscopic partial nephrectomy: Step-by-step contemporary technique and surgical outcomes at a single high-volume institution. Eur Urol, 2012; 62:553–561.

Zorn

, Gong

, Mendiola

, et al. Operative outcomes of upper pole laparoscopic partial nephrectomy: Comparison of lower pole laparoscopic and upper pole open partial nephrectomy. Urology, 2007; 70:28–34.

10.

Ishiyama

, Kondo

, Takagi

, et al. Impact of the Mayo adhesive probability score on the complexity of robot-assisted partial nephrectomy. J Endourol, 2018; 32:928–933.

11.

Motoyama

, Matsushita

, Watanabe

, et al. Initial learning curve for robot-assisted partial nephrectomy performed by a single experienced robotic surgeon. Asian J Endosc Surg, 2020; 13:59–64.

12.

Mottrie

, De Naeyer

, Schatteman

, et al. Impact of the learning curve on perioperative outcomes in patients who underwent robotic partial nephrectomy for parenchymal renal tumours. Eur Urol, 2010; 58:127–132.

13.

Kondo

, Takagi

, Morita

, et al. Early unclamping might reduce the risk of renal artery pseudoaneurysm after robot-assisted laparoscopic partial nephrectomy. Int J Urol, 2015; 22:1096–1102.

14.

Davidiuk

, Parker

, Thomas

, et al. Mayo adhesive probability score: An accurate image-based scoring system to predict adherent perinephric fat in partial nephrectomy. Eur Urol, 2014; 66:1165–1171.

15.

Matsuo

, Imai

, Horio

, et al. Revised equations for estimated GFR from serum creatinine in Japan. Am J Kidney Dis, 2009; 53:982–992.

16.

Dindo

, Demartines

, Clavien

. Classification of surgical complications: A new proposal with evaluation in a cohort of 6336 patients and results of a survey. Ann Surg, 2004; 240:205–213.

17.

Faries

and SAS

Institute

.: Analysis of observational health care data using sas. SAS Publishing: Cary, North Carolina, 2010.

18.

Macleod

, Hsi

, Gore

, Wright

, Harper

. Perinephric fat thickness is an independent predictor of operative complexity during robot-assisted partial nephrectomy. J Endourol, 2014; 28:587–591.

19.

Diana

, Lughezzani

, Uleri

, et al. Multi-institutional retrospective validation and comparison of the simplified PADUA REnal Nephrometry System for the prediction of surgical success of robot-assisted partial nephrectomy. Eur Urol Focus, 2021; 7:1100–1106.

20.

Khene

, Peyronnet

, Kocher

, et al. Predicting morbidity after robotic partial nephrectomy: The effect of tumor, environment, and patient-related factors. Urol Oncol, 2018; 36:338.e319–338.e326.

21.

Veccia

, Antonelli

, Uzzo

, et al. Predictive value of nephrometry scores in nephron-sparing surgery: A systematic review and meta-analysis. Eur Urol Focus, 2020; 6:490–504.

22.

Alvim

, Audenet

, Vertosick

, Sjoberg

, Touijer

. Performance prediction for surgical outcomes in partial nephrectomy using nephrometry scores: A comparison of arterial based complexity (ABC), RENAL, and PADUA systems. Eur Urol Oncol, 2018; 1:428–434.

23.

Ficarra

, Porpiglia

, Crestani

, et al. The Simplified PADUA REnal (SPARE) nephrometry system: A novel classification of parenchymal renal tumours suitable for partial nephrectomy. BJU Int, 2019; 124:621–628.

24.

Cacciamani

, Gill

, Medina

, et al. Impact of host factors on robotic partial nephrectomy outcomes: Comprehensive systematic review and meta-analysis. J Urol, 2018; 200:716–730.