Vascularized Parenchymal Mass Preserved with Partial Nephrectomy: Functional Impact and Predictive Factors

Background: Percentage parenchymal mass preserved (PPMP) is a key determinant of functional outcomes after partial nephrectomy (PN); however, predictors of PPMP have not been defined. Objective: To provide a comprehensive analysis of the functional impact of and potential predictive factors for PPMP. Design, setting, and participants: We analyzed data for 464 patients managed with PN at our center with necessary studies to determine vascularized parenchymal mass and function preserved within the operated kidney. PPMP was measured from computed tomography scans <2 mo before and 3–12 mo after PN. Intervention: PN. Outcome measurements/statistical analysis: Recovery from ischemia was defined as percentage ipsilateral glomerular filtration rate (GFR) preserved normalized by PPMP. We used Pearson correlation to evaluate the relationships between GFR preserved and PPMP. Multivariable logistic regression was used to assess predictors of PPMP. Result and limitations: Ninety-six patients (21%) had a solitary kidney. The median tumor size and RENAL score were 3.5 cm and 8, respectively. Cold/warm ischemia were utilized in 183/281 patients for which the median ischemia time were 28/20 min. The median preoperative and postoperative vascularized parenchymal mass in the operated kidney were 194 and 157 cm³, respectively, resulting in median PPMP of 84%. GFR preservation correlated strongly with PPMP (r = 0.64; p < 0.001). Recovery from ischemia was suboptimal (<80%) in 71 patients (15%), while suboptimal PPMP (<80%) was a more common adverse event, occurring in 160 patients (34%; p < 0.001). Multivariable analysis demonstrated that greater tumor size and complexity were associated with lower PPMP (p ≤ 0.04), while solitary kidney and hypothermia were associated with higher PPMP (p < 0.001). Longer ischemia time was also associated with lower PPMP (p = 0.003), probably reflecting the complexity of the surgery. Limitations include the retrospective design. Conclusion: PPMP correlates strongly with functional outcomes after PN, and lower PPMP is the most common and important source of functional decline after PN. Larger tumors, greater tumor complexity, and prolonged ischemia time were associated with lower PPMP, while PPMP tended to be greater for solitary kidneys, confirming that PPMP is a modifiable factor. Patient summary: Kidney function after partial nephrectomy primarily depends on the amount of vascularized kidney preserved by the procedure. Lower recovery of function is seen when operating on larger tumors in unfavorable locations, but preservation of the parenchymal mass can be improved when truly necessary, such as when operating on a tumor in a solitary kidney. Suboptimal percentage parenchymal mass preservation (PPMP) is the predominant cause of lower functional recovery after partial nephrectomy. Larger tumors and greater tumor complexity are associated with lower PPMP, while PPMP was greater for tumors in a solitary kidney, suggesting that PPMP is a modifiable parameter.