R.E.N.A.L. Nephrometry Score Predicts Non-neoplastic Parenchymal Volume Removed during Robotic Partial Nephrectomy

Objective: To assess the association between the R.E.N.A.L. Nephrometry score, the amount of non-neoplastic parenchymal volume (NNPV) removed, and the renal function decline in patients undergoing robotic partial nephrectomy (RPN). Patients and Methods: The Multi-institutional Mount Sinai Kidney Cancer Database was used to identify 1235 patients who underwent RPN between January 2008 and February 2016, of whom 366 had complete data, including NNPV removed. Mann-Whitney U tests and univariable linear regression models were used to assess the relationships between R.E.N.A.L. Nephrometry score, warm ischemia time (WIT), and NNPV removed. Univariable and multivariable regression models were then used to assess the independent relationships of each of these variables with percent change in estimated glomerular filtration rates (eGFR) and acute kidney injury (AKI) within the first 30 postoperative days in addition to percent change in eGFR and progression to chronic kidney disease at a median follow-up of 6.9 months. Results: Increasing R.E.N.A.L. Nephrometry score was shown to be a predictor of WIT (β = 0.92, p < 0.001) and of NNPV removed (β = 6.21, p < 0.001) in univariable analyses. In multivariable analysis, postoperative reduction in eGFR within the first 30 days of surgery was associated with both R.E.N.A.L. Nephrometry score (β = -2.02, p < 0.001) and NNPV removed (β = -5.19, p = 0.015). R.E.N.A.L. Nephrometry score (OR = 1.21, p = 0.013) and NNPV removed (OR = 1.90, p = 0.013) were also associated with an increased likelihood of AKI within the first 30 days. No significant association in this cohort was found between R.E.N.A.L. Nephrometry score, NNPV removed, or WIT and renal function decline at 6.9 months. Conclusion: The preoperative R.E.N.A.L. Nephrometry score can be used to predict postoperative pathologically determined healthy renal volume loss or NNPV removed. Removal of not just the tumor but also the healthy surrounding parenchyma is important in determining renal function decline. As our understanding of the importance of renal volume loss grows, NNPV removed gains increasing utility as an easily determinable postoperative variable.