Purpose or Case Report: There is no standardized system for assessment of which pediatric tumors are amenable to partial nephrectomy – a surgery that is considered in pediatric patients with bilateral renal masses and those with predisposition syndromes. The RENAL Nephrometry score is the most widely used system to assess renal tumor complexity for surgical decision making in adults. We evaluated the RENAL Nephrometry score and imaging features that might predict perioperative clinical outcomes.
Methods & Materials: An IRB approved urological database was searched for all patients who underwent partial nephrectomy for a renal mass from 2006-2019. Pre-op CT/MR imaging was anonymized for review. Following training sessions, 2 pediatric radiologists and 2 pediatric urologists scored images using a 14-question survey instrument that included RENAL Nephrometry features of tumor size, distance from the collecting system, and location in the kidney. Patients were grouped based on Nephrometry score (low complexity:<9, high complexity: >9). Fleiss's kappa and the intraclass correlation coefficient (ICC) were performed in R. Consensus Nephrometry scores were calculated using the median (continuous numeric variables) and mode (categorical variables). Outcome data was obtained from the EMR.
Results: 28 patients had 33 surgeries. Median age at surgery was 3.2 years old (IQR: 1.8-4.0). 17 patients (52%) were female and 14 (42%) had renal mass predisposition syndromes- most commonly Beckwith Wiedemann Syndrome (n=7; 21.2%). The cross-sectional imaging closest to surgery was MR for 27 and CT for 7 patients. Mean imaging-to-OR time was 15 days (Range: 7-44 days).

Good-to-excellent agreement was seen for tumor size (ICC=0.91), distance from collecting system (ICC=0.72), and exophytic nature of the tumor (ICC=0.77) (ps<0.001). Moderate-to-substantial agreement for whether the tumor crossed the renal midline (κ=0.74) and whether the tumor touched the hilar vessels (κ=0.56) (ps<0.001).

Median Nephrometry score = 9 (range:4 - 11). High complexity tumors were associated with longer OR times (367 vs 267 min, p=0.003), increased length of stay (7 vs 4 days, p=0.006), and higher estimated blood loss (275 vs 200, p=0.28).
Conclusions: A standardized morphologic scoring system of renal tumors is reproducible, correlates with perioperative outcomes, and therefore has promise for pediatric patients undergoing partial nephrectomy. High tumor complexity correlated with increased hospital stay, operative time and blood loss at resection.