Standardized Reporting of Resection Technique During Nephron-sparing Surgery: The Surface-Intermediate-Base Margin Score

Nephron-sparing surgery (NSS) is the reference standard for the treatment of renal masses of <4 cm. Both the European Association of Urology (EAU) and the American Urological Association guidelines support routine use of NSS for T1 tumors [1,2], as NSS affords conservation of normal renal parenchyma while preserving oncologic efficacy. Since the initial description of NSS [3], a number of technical strategies for excision of the tumor from normal renal parenchyma have been described. These strategies can be grouped into three main categories: simple enucleation (SE), enucleoresection (ER), and wedge resection (WR). Unfortunately, standardized definitions for each technique are lacking. Indeed, the descriptors SE, ER, and WR are used largely interchangeably. The precise resection methodology is rarely reported [4], despite a relationship between technique and complication rates, preserved parenchymal volume, surgical margins (SMs), local recurrence, and oncologic outcomes [3,5]. Debates regarding the optimal width of a normal parenchymal margin around the tumor persist in the literature. Emphasis is placed on complete resection of the tumor, while the extent of the healthy margin size does not appear to correlate with local recurrence [5]. Of note, current guidelines state that a ‘‘minimal’’ tumor-free SM is sufficient to avoid local recurrence, without specifying its exact thickness [1,2]. Despite this, the prudence of SE is often debated [5]. Although SE has been defined as a safe minimal partial nephrectomy (PN) ‘‘in perfect harmony’’ with the EAU guidelines, questions regarding the interpretation ofSMsand oncologic safety remain [6,7]. In practice, these three methods may all be used in the same case, with WR more likely at the peripheral cortex, ER in the medulla, and SE at the bottomof the resection as the tumor is reduced fromthe collecting system or the renal sinus fat [6]. Few NSS series address or describe which particular resection technique was used, thereby undermining meaningful comparisons and interpretations of the literature [3,8,9]. This lack of uniformity and inconsistent nomenclature hinder progress and limit effective communication by rendering comparisons of various surgical series difficult. The literature fully ignores mixed resection techniques, as described. Given the relationship between techniques and outcomes aswell as the recognized $().2DFGIT[]gi importance of standardized training models for surgical education, especially for robotic surgery [10], an accurate definition ofNSS resection techniques could improve the planning for modular training.Webelieve that a standardized reporting system to communicate tumor resection technique is important and propose amodel based on an analysis of the margin of healthy parenchyma visually scored at the superficial surface, the intermediate surface, and the base of the tumor: the surface–intermediate–base (SIB) scoring system. Standardized definitions should include resection to designate removal of the tumor with a substantial margin in which the contour of the tumor cannot be visualized through the resected parenchyma; ER, in which there is a minimal margin (1 mm) of normal parenchyma that allows for clear visualization of the tumor’s contours; and enucleation, in which only a tumor’s pseudocapsule is seen, without resection of surrounding tissue (margins less than approximately 1 mm) [11,12]. In all cases, there should be no violation of the pseudocapsule. The SIB scoring system for standardized reporting ofNSS resection techniques is presented in Figure 1. The surface of each area is circumferentially analyzed by the surgeon, and the minimal margin of each area is recorded. The score is first assigned to the resection method at the superficial interface of the tumor and the renal parenchyma. Zero points are assigned for enucleation,while 1 point is given to ER or resection. Points are then assigned to the intermediate and to the deepest portions of the tumor as they relate to the renal parenchymal surface. Zero, 1, or 2 points are given for enucleation, ER, or resection, respectively (Fig. 1). Higher point value designates a wider margin. In this manner, resection that first begins with a wide margin at the surface but cones down to a ‘‘peel away’’ at the tumor base can be easily reported. At the extremes this would mean that a tumor that is excised with a full rim of normal parenchyma is scored as 1 + 2 + 2 = 5, while a fully enucleated resection is scored as 0 + 0 + 0 = 0. The SIB score is designed so that the score sum can be grouped into the following resection subtypes: pure enucleation (SIB sum: 0 or 1), hybrid enucleation (SIB sum: 2), pure ER (SIB sum: 3), hybrid ER (SIB sum: 4), and resection (SIB sum: 5) (Fig. 2). A subscript c should designate a capsulotomymade during the resection. Use of such a surgeon-based, visually assigned quantification system would achieve a precise anatomic grading of PN. In summary, we believe that (1) the lack of standardized terminology to describe NSS technique, (2) the current inability to communicate the complexity that may be inherent in a given tumor’s resection, and (3) the nearly complete absence of routine reporting of resection type potentially undermine the interpretation of NSS outcomes and prohibit meaningful comparisons of results among surgeons and institutions. We believe that the SIB standardized reporting methodology that we propose will enable quantification of resection technique, will significantly raise the quality of the reported NSS data, and thus will make outcome assessments and comparisons of surgical series more meaningful. Because intraoperative variables can change the surgical strategy, a standardized reportingsystem that takes into account the actual surgical result represents an important change toward objectification.