The Volume of Nonneoplastic Parenchyma in a Minimally Invasive Partial Nephrectomy Specimen: Predictive Factors and Impact on Renal Function

Purpose: To identify predictors of nonneoplastic parenchymal volume excised during minimally invasive partial nephrectomy (PN) and determine the impact on postoperative renal function. Patients and Methods: A total of 206 patients underwent laparoscopic or robot-assisted PN between 2003 and 2011. Parenchymal volume was estimated by subtraction of calculated tumor volume from total specimen volume. Univariate and multivariate regression analyses were used to examine the association of parenchymal volume with tumor and surgical factors. Percent and absolute changes in estimated glomerular filtration rate (eGFR) on the day after surgery, 1 to 12 months, and >12 months after surgery were correlated with parenchymal volume. Results: Increased tumor size (P<0.001), earlier era of surgery (P=0.04), and longer ischemia time (P=0.05) were associated with higher parenchymal volume. Robotic surgery was not associated with better parenchymal preservation. Median percent change in eGFR at 1 to 12 months (mean=6.7 months) and >12 months (mean=28.3 months) was -10.9% and -12.1%, respectively. No association was found between the volume of parenchyma and change in eGFR. Longer ischemia time was associated with decrease in eGFR only the first day after surgery (P=0.005). Higher body mass index BMI and Charlson comorbidity index and lower preoperative eGFR were associated with decrease in eGFR 1 to 12 months after surgery (P=0.006, 0.04, 0.001, respectively). Conclusions: In our cohort, larger tumors, longer ischemia time, and earlier era of PN were associated with increased amount of nonneoplastic parenchyma excised during surgery. We did not observe a relationship between absolute volume of parenchyma and change in renal function after surgery. Baseline renal function and comorbidities were the strongest determinants of long-term renal function.