BEYOND THE COMPLEXITY OF TUMOR EXCISION DURING PARTIAL NEPHRECTOMY:IDEATION AND HISTOPATHOLOGICAL VALIDATION OF THE SURFACE-INTERMEDIATEBASE (SIB) MARGIN SCORE

Introduction/Aim: Tumor excision is a fundamental step during partial nephrectomy (PN), yet resection technique (RT) is rarely reported in current nephron-sparing surgery (NSS) literature. We recently proposed the Surface-Intermediate-Base (SIB) margin score as a new classification model for standardized reporting of RT during NSS. The aim of the study was to validate the SIB model from a histopathological perspective. Materials and Methods: Data were prospectively collected from a cohort of 40 patients undergoing NSS, between June and September 2014, at a single Institution. The SIB score was assigned in the operating room by the surgeon. The score-specific areas (SSA) were outlined on a digital picture as anatomic landmarks for histopathological analysis. Two dedicated uropathologists inked the landmark areas and measured, in a blinded fashion, the maximum, minimum and mean thickness of healthy renal margin (HRM) within the SSAs (360 overall histologic measures, Figure 1). The Mann- Whitney U-test was used to assess the correlation between the SIB visual definitions of RTs and the thickness of HRM at histopathological analysis. Results: The overall RT was classified as pure enucleation, hybrid enucleation and pure enucleoresection in 28 (70%), 7 (17%) and 3 (7%) patients, respectively, while as hybrid enucleoresection and resection in 1 (3%) patient each. At histopathological analysis, the maximum, minimum and mean thickness of HRM was significantly different among SSAs visually defined as enucleation (S=0: median=0.18mm (interquartile range (IQR)=0.08-0.30), I or B=0: median=0.20 mm (IQR=0.08- 0.36)), enucleoresection (S=1: median=0.80 mm (IQR=0.67- 1.16), I, B=1: median=0.88 mm (IQR=0.60-1.00)) and resection (S=1, I, B=2: median=2.95 mm (IQR=2.18-5.75). (Figure 2) (p<0.001). Conclusion: The SIB margin score is the first standardized reporting system to communicate RT during NSS. Our study proved the applicability of the model in a realworld clinical setting and provided robust histopathological validation of its utility.