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Background: Currently, no standard manner exits to compare renal tumor complexity in children and adolescents, making it impossible to speak a “common language” when comparing lesions and the impact of tumor complexity on surgery and outcomes. Recently, such a standardized system has been developed in adults. The RENAL nephrometry system is a valid instrument across institutions and between users which reliably predicts tumor complexity and clinical outcomes such as the ability to complete partial nephrectomy (PN) and the incidence of peri-operative complications. We propose that such a standardized system would be a useful in children, adolescents, and young adults with renal masses. Our goal was to describe RENAL nephrometry in such a population and correlate this score with surgical and pathologic outcomes.
Materials and Methods: We reviewed all patients at our institution who underwent resection of a renal malignancy between 2002-13, and who had pre-operative, contrast-enhanced, cross-sectional imaging available. We assessed the RENAL nephrometry score for each affected kidney. RENAL nephrometry is based on 5 features characterizing renal tumor anatomy as they relate to resectability. Each feature in the score is designated by a letter: (R)adius (maximal tumor diameter), (E)xophytic/endophytic tumor, (N)earness of tumor to collecting system or sinus, (A)nterior (a)/posterior (p)/both(x) descriptor and (L)ocation relative to polar line(PL). R-scoring - 1:≤4cm, 2:4-7cm, 3:≥7cm. E-scoring - 1:≥50%Exophytic, 2:<50%Exophytic, 3:Entirely endophytic. N-scoring - 1:≥7mm, 2:4-7mm, 3:≤4mm. L-scoring - 1:Entirely above upper PL or below lower PL, 2:Crosses the PL, 3:>50% of mass across PL or mass crosses axial renal midline or entirely between the PL. The mass is assigned low (4-6), moderate (7-9) or high (10-12) complexity based on the RENL sum score. We then compared tumor characteristics and outcomes between the groups of low, moderate, and high complexity masses.
Results: We identified 65 patients and 67 kidneys meeting study criteria. Median age at diagnosis was 3.5yr (0.1-27.6). 36 kidneys were imaged with CT and 31 with MRI. We identified 5 low-complexity, 10 moderate-complexity, and 52 high-complexity lesions (Table). In comparing the clinical and pathologic features between groups, we observed that less complex masses were observed in older patients, more commonly managed with PN, and more often represented Renal Cell Carcinoma (RCC), and non-Wilms Tumor (WT) pathology. We did not observe a statistically significant correlation between tumor complexity and EBL, Operative time, Intraoperative transfusion, Positive margins, or Tumor rupture.
Conclusion: Renal lesions in this population are generally of high-complexity. RENAL nephrometry appears most useful in evaluating and discriminating RCC and masses in older children and adolescents. However, it requires further refinement to capture nuances in distinguishing the complexity of other pediatric renal malignancies such as WT.
Table: Comparison of Renal Masses with Low, Moderate, and High Complexity RENAL Nephrometry Scores

	Low Complexity N=5	Moderate Complexity N=10	High Complexity N=52	Overall p-value	Low vs. Mod p-value	Mod vs. High p-value	Low vs. High p-value
Age at Diagnosis (Years)	15.9 (3.1-27.6)	6.7 (0.1-17.7)	3.3 (0.1-23.3)	0.009	0.075	0.11	0.006
Sex	1M:4F	4M:6F	28M:24F	0.29	0.6	0.52	0.194
R - Largest tumor diameter				<0.001	0.5	<0.001	<0.001
1: ≤4cm	5 (100%)	7 (70%)	3 (5.8%)
2: 4 to 7cm	0 (0%)	3 (30%)	4 (7.7%)
3: ≥7cm	0 (0%)	0 (0%)	45 (86.5%)
E - % Exophytic				<0.001	0.001	0.36	<0.001
1: ≥50%	4 (80%)	3 (30%)	0 (0%)
2: <50%	1 (20%)	7 (70%)	8 (15.4%)
3: Entirely Endophytic	0 (0%)	0 (0%)	44 (84.6%)
N - Nearness to CS/Sinus				<0.001	0.004	1	<0.001
1: ≥7mm	4 (80%)	0 (0%)	0 (0%)
2: 4 to 7mm	1 (20%)	0 (0%)	0 (0%)
3: ≤4mm	0 (0%)	10 (100%)	52 (100%)

	Low Complexity N=5	Moderate Complexity N=10	High Complexity N=52	Overall p-value	Low vs. Mod p-value	Mod vs. High p-value	Low vs. High p-value
A - Ant vs. Post Location				0.012	0.74	0.003	0.22
a: Completely Anterior	2 (40%)	3 (30%)	10 (19.2%)
p: Completely Posterior	1 (20%)	4 (40%)	3 (5.8%)
x: Both	2 (40%)	3 (30%)	39 (75.0%)
L - Location relative to PLs				<0.001	0.007	<0.001	<0.001
1:	5 (100%)	2 (20%)	0 (0%)
2:	0 (0%)	8 (80%)	3 (5.8%)
3:	0 (0%)	0 (0%)	49 (94.2%)
Sum Score	4: 2 (40%)	7: 0 (0%)	10: 6 (11.5%)
	5: 2 (40%)	8: 2 (20%)	11: 11 (21.2%)
	6: 1 (20%)	9: 8 (80%)	12: 35 (67.3%)
Surgery
Radical Nephrectomy (RN)	2 (40%)	3 (30%)	51 (98.1%)	<0.001	1	<0.001	0.001
Partial Nephrectomy (PN)	3 (60%)	7 (70%)	1 (1.9%)
Completed Case as PN	3 (100%)	7 (100%)	1 (100%)
Positive Margin	1 (20%)	1 (10%)	5 (9.6%)	0.77	1	1	0.44
Tumor Spill	0 (0%)	0 (0%)	3 (5.8%)	0.64	1	1	1
EBL (mL)	75 (25-700)	150 (65-550)	50 (5-1860)	0.31	0.76	0.19	0.35
Intraoperative Transfusion	1 (20%)	2 (20%)	12 (23.1%)	0.97	1	1	1
Operative Time (min)	199 (159-240)	261.5 (215-508)	283.5 (77-711)	0.22	0.34	0.98	0.08
Pathology				0.014	0.45	0.039	0.006
Wilms Tumor	1 (20%)	4 (40%)	37 (71.2%)
Renal Cell Carcinoma	4 (80%)	3 (30%)	4 (7.7%)
CCSK	0 (0%)	0 (0%)	4 (7.7%)
Congenital MN	0 (0%)	1 (10%)	2 (3.8%)
Rhabdomyosarcoma	0 (0%)	0 (0%)	2 (3.8%)
IMT	0 (0%)	1 (10%)	0 (0%)
Fibrosarcoma	0 (0%)	0 (0%)	1 (1.9%)
JGA Tumor	0 (0%)	1 (10%)	0 (0%)
MCN	0 (0%)	0 (0%)	1 (1.9%)
Metanephric Adenoma	0 (0%)	0 (0%)	1 (1.9%)
RCC vs.	4 (80%)	3 (30%)	4 (7.7%)	<0.001	0.12	0.076	0.194
All other pathologies	1 (20%)	7 (70%)	48 (92.3%)
Wilms Tumor/CCSK vs.	1 (20%)	4 (40%)	41 (78.8%)	0.003	0.6	0.02	0.014
All other pathologies	4 (80%)	6 (60%)	11 (21.2%)