Objective: The aim of the present study was to explore the utility of mathematically calculated tumor contact surface area (CSA), which has been introduced as a predictor of postoperative renal function, in patients who underwent partial nephrectomy (PN) for solitary renal mass at Siriraj Hospital – Thailand’s largest national tertiary referral center.

Materials and Methods: The authors retrospectively reviewed all patients who underwent PN as the management of solitary renal mass from 2012 to 2017 at Siriraj Hospital, Bangkok, Thailand. Only patients who had available pre-operative imaging and serum creatinine before and after PN were included. CSA was calculated using the formula 2πrd, where r = tumor radius, and d = intraparenchymal depth of tumor from preoperative computed tomography or magnetic resonance imaging. Estimated glomerular filtration rate (eGFR) was estimated by Chronic Kidney Disease Epidemiology formula. Postoperative eGFR was based on the best serum creatinine level within a year after surgery. Spearman’s correlation coefficient, univariate, and multivariate linear regression analyses were utilized to identify factors associated with percent eGFR change (PCE) after PN.

Results: Of 67 patients, the mean age was 58.3+12.5 years and 43 (64.2%) were male. Median tumor size, R.E.N.A.L. score, and CSA was 2.8 cm (interquartile range [IQR]: 2.2 to 3.5), 7 (IQR: 6 to 9), and 16.1 cm2 (IQR: 9.8 to 23.8), respectively. Open PN was performed in 32 patients (47.8%), and minimally invasive PN was performed in 35 patients (52.2%). Median preoperative and postoperative eGFR was 77 (IQR: 53 to 89) and 70 (IQR: 53 to 87) ml/min/1.73 m2, respectively. Median absolute eGFR change (ACE) was 4.6 ml/
min/1.73 m2 (IQR: 0.0 to 12.1), and the median PCE was 4.6% (IQR: 0.0 to 4.6). CSA was found to be significantly correlated with R.E.N.A.L. score (r = 0.55, p<0.001); however, neither CSA nor R.E.N.A.L. score was significantly associated with ACE or PCE. Multivariate analysis showed that male gender (p = 0.02) and cardiovascular disease (p = 0.03) were significantly associated with PCE.

Conclusion: Although calculated CSA from pre-operative imaging was feasible to predict postoperative renal function after PN, it failed to be associated with postoperative renal function in our study. Further study is needed to validate the utility of this technique.

Keywords: Partial nephrectomy, Renal mass, Contact surface area, Tumor contact surface area