Tumor Contact Surface Area As a Predictor of Functional Outcomes After Standard Partial Nephrectomy: Utility and Limitations

Objective: To evaluate contact surface area (CSA) between the tumor and parenchyma as a predictor of ipsilateral parenchyma and function preserved after partial nephrectomy (PN). Previous studies suggested that CSA is a strong predictor of functional outcomes but the limitations of CSA have not been adequately explored. Patients and Methods: Four hundred nineteen patients managed with standard PN for solitary tumor with necessary studies to evaluate and analyze ipsilateral preoperative or postoperative parenchymal mass and function. Parenchymal mass and CSA were measured using contrast-enhanced computed tomography <2 months prior and 3-12months after PN. CSA was calculated: 2πrd, where r = radius and d = intraparenchymal depth. Pearson-correlation evaluated relationships between CSA and ipsilateral parenchymal mass or function preserved. Multivariable regression assessed predictors of function preserved. Conceptually, the CSA paradigm should function better for exophytic tumors than endophytic ones. Results: Median tumor size was 3.5 cm and R.E.N.A.L. was 8. Median global and ipsilateral glomerular filtration rate preserved were 89% and 79%, respectively. Median ipsilateral parenchymal mass preserved was 85% and significantly higher for exophytic masses (P =.001). Median CSA was 22.8 cm² and significantly less for exophytic masses (P =.02). CSA associated with both ipsilateral function and mass preserved (both P <.05), but the correlations were only modest (r = 0.25 and 0.36, respectively). On multivariable analysis, CSA associated with function preserved for exophytic masses (P =.01), but not for endophytic ones (P =.27). Conclusion: CSA associates with functional outcomes after standard PN, although the strength of the correlations was modest, unlike previous studies, and CSA was not an independent predictor for endophytic tumors. Further study will be required to evaluate the utility of CSA in various clinical settings.