Kidney cancer. Principles and practice. Second edition. Primo N. Lara, Jr. Eric Jonasch (Editors). Springer International Publishing (2015)
Despite, or because of, the myriad treatment options available to the patient and treating urologist, clinical decision making for localized RCC is overly subjective. It is based on numerous often qualitative factors, including competing health risks (real or perceived), the interpreted tumor anatomy, physician experience and comfort, and patient preference/perceptions of the ease/efficacy of various treatment modalities.
We introduced the RENAL nephrometry scoring system as a means to objectify the salient anatomic features of a renal mass on crosssectional imaging. This system may be utilized to compare outcomes and develop metrics for treatment decision making  (Fig. 9.2). In the absence of a common nomenclature to describe the anatomical attributes of a renal tumor, treatment decision making is subject to an unmeasured physician’s biases and individual experience. A tumor’s nephrometry score is a structured and quantifiable method to describe the tumor’s relevant anatomical features as they relate to the complexity of a tumor, its difficulty of resection, and potential treatment risks.
The scoring system is based on the five most reproducible features that characterize the anatomy of a solid renal mass: (R)adius (scores tumor size as maximal diameter), (E)xophytic/ endophytic properties of the tumor, (N)earness of the deepest portion of the tumor to the collecting system or renal sinus, (A)nterior (a)/posterior (p) descriptor, and (L)ocation relative to the polar line. All components except for the (A) descriptor are scored on a 1-, 2-, or 3-point scale. The (A) describes the principal mass location to the coronal plane of the kidney. The suffix “x” is assigned to the tumor if an anterior or posterior designation is not possible. An additional suffix “h” is used to designate a hilar location of the tumor (abutting the main renal artery or vein).
The RENAL nephrometry scoring system represents the first-introduced method to attempt to standardize the reporting of the salient anatomy of an enhancing renal mass. Subsequently, the PADUA score was introduced as another objective method to describe the anatomical features of a renal mass . The PADUA score is remarkably similar to nephrometry with the exception of “the definition of the sinus lines and the evaluation of the anatomical relationship between the tumor and urinary collecting system or renal sinus” . Lastly, the C-Index Method was introduced to characterize a tumor’s centrality. This method requires a complex geometric calculation using cross-sectional imaging to determine the distance from the tumor center to the center of the kidney . We believe that the RENAL nephrometry scoring system is unique in that it is an accessible system that can be learned rapidly and applied that reliably describes the most salient renal mass features.
By creating a reproducible system based on the renal mass anatomy, we have objectified the descriptions of renal masses that previously were simply referred to in terms such as “simple” or “difficult,” thereby creating a platform to ascertain the optimal surgical approach. For example, in a recent evaluation of our institutional database, 94% of low-complexity (nephrometry score = 4–6) masses were treated with a PN, most using an MIS technique. Nephrometry has several additional uses beyond aiding in surgical treatment decision making. Recent investigators have adopted nephrometry to examine its ability to predict for functional, perioperative, and pathologic outcomes. Cha et al. showed that patients with higher “nephrometric variables,” (R) and (E), were more likely to experience postoperative renal impairment after a MIS-PN . Two other groups have shown that higher nephrometry scores predict for increased blood loss and longer ischemia time when undergoing either MIS-PN or open PN [34, 35]. Additionally, a prospective study at our institution validated that higher nephrometry scores can be used to predict prolonged warm ischemia time . Finally, despite prior work reporting no significant biological differences between centrally and peripherally located tumors , nephrometry was recently evaluated to determine its ability to preoperatively predict the histology and grade of enhancing renal masses. In this work, the authors found a high correlation between nephrometry score and tumor grade (p < 0.0001) and histology (p < 0.0001) . Specifically, papillary RCCs had the lowest total nephrometry score, while clear cell RCCs had higher nephrometry scores. Furthermore, benign lesions tended to be smaller, more endophytic, and non-hilar .
Nephrometry creates a platform to standardize salient renal mass anatomy. In doing so, objective treatment decision making can be performed when the urologist considers the functional, perioperative, and preoperative pathologic information that one can derive from the RENAL nephrometry scoring system.
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