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Since the advent of the first standardized renal tumor complexity system, many subsequent scoring systems have been introduced, many of which are complicated and can make it difficult to accurately measure data end points. In light of these limitations, we introduce the new zonal NePhRO scoring system.
Patients and Methods
The zonal NePhRO score is based on 4 anatomical components that are assigned a score of 1, 2, or 3, and their sum is used to classify renal tumors. The zonal NePhRO scoring system is made up of the (Ne)arness to collecting system, (Ph)ysical location of the tumor in the kidney, (R)adius of the tumor, and (O)rganization of the tumor. In this retrospective study, we evaluated patients exhibiting clinical stage T1a or T1b who underwent open partial nephrectomy performed by 2 genitourinary surgeons. Each renal unit was assigned both a zonal NePhRO score and a RENAL (radius, exophytic/endophytic properties, nearness of tumor to the collecting system or sinus in millimeters, anterior/posterior, location relative to polar lines) score, and a blinded reviewer used the same preoperative imaging study to obtain both scores. Additional data points gathered included age, clamp time, complication rate, urine leak rate, intraoperative blood loss, and pathologic tumor size.
One hundred sixty-six patients underwent open partial nephrectomy. There were 37 perioperative complications quantitated using the validated Clavien-Dindo system; their occurrence was predicted by the NePhRO score on both univariate and multivariate analyses (P = .0008). Clinical stage, intraoperative blood loss, and tumor diameter were all correlated with the zonal NePhRO score on univariate analysis only.
The zonal NePhRO scoring system is a simpler tool that accurately predicts the surgical complexity of a renal lesion.
During this same period, the advent of nephron-sparing surgery (NSS) has emerged as an oncologic equivalent surgical option for managing SRMs. When determining if a patient is a suitable candidate for NSS and which surgical approach will be adopted, it is critical to assess renal tumor anatomy and complexity. Urologists are left with the quandary of how to best quantify and standardize renal tumor complexity. The development of a universal complexity scoring system is imperative to (1) facilitate interphysician communication, (2) better quantitate risk assessment among patients, and (3) help characterize the likelihood of perioperative complications, being that yearly litigation rates are 11% among urologists.
Since 2009, 4 distinct renal tumor complexity scoring systems have been proposed to quantify renal tumor characteristics. The RENAL nephrometry scoring system was the first described and is based on 5 aspects (radius, exophytic/endophytic properties, nearness of tumor to the collecting system or sinus in millimeters, anterior/posterior, location relative to polar lines) of the preoperative cross-sectional imaging study.
Ficarra et al later proposed the PADUA classification system based on 7 parameters (tumor size, longitudinal location, renal rim location, exophytic rate, renal sinus involvement, urinary collecting system involvement, and anterior or posterior face).
The first 3 mentioned scoring systems have been tested and validated in relation to their correlation with warm ischemia time, with the C-index system showing the best relative correlation with this treatment end point.
It appears that although each system purports to identify renal tumor complexity, they are not all measuring the same characteristics of the tumors with regard to its anatomical relation to the renal unit. In certain cases, the system uses numbers and letters, which complicates the scoring system further.
In light of these great strides made in the nephrometry system since its inception, the aim of the present study was to define a simplified numeric scoring system based solely on tumor characteristics and physical attributes of the kidney but also encompassing the key features of the current nephrometry scoring system. It was forged from the strengths of the RENAL scoring system and built on some of its limitations. This new system differentiates itself from the other scoring tools by dividing the kidney and the tumor into discrete anatomical zones and avoids cumbersome use of numbers with letters and observer-dependent polar lines.
Patients and Methods
The surgical approach to any SRM is centered predominantly around 4 critical tumor parameters (as measured on preoperative imaging): size, location of the mass within the kidney, relationship to the collecting system, and spatial relationship of tumor to other organs or important vascular anatomy. In light of these parameters, we created a novel scoring system termed the zonal NePhRO scoring system—the first 2 components divide the kidney into anatomical zones and the latter 2 components divide the tumor into zones to assist with scoring. All the anatomical components are assigned a score of 1, 2, or 3. Once all 4 parameters have been scored, the individual numbers are tallied. This final cumulative score classifies the renal tumor as a low-, moderate-, or high-complexity renal tumor.
The first renal constituent is the tumor's (Ne)arness to the collecting system. It is quantified not by length in centimeters but by renal parenchymal architecture, such as cortical or medullary, or by its contact with the collecting system. Each segment of the renal architecture is denoted as a zone, as shown in Figure 1, and the renal unit is assigned a number based on its location within a given zone. If the tumor is located solely within the cortex, it is assigned 1 point; if it is within the renal medulla, 2 points are given. Finally, if the tumor is in contact with the collecting system or the inner lining of the renal parenchyma, it is given 3 points.
The second renal component is the (Ph)ysical location of the tumor within the kidney in relation to the renal architecture. This is similarly divided into 3 respective zones as shown in Figure 1. Zone 1 is allocated to any tumor located in the lower pole of the kidney below the collecting system, thus obviating the need for polar lines. Zone 2 is assigned to a tumor located lateral to all of the collecting system but not touching the collecting system. It must also not be part of the upper pole or lower poles, as defined as being beyond the collecting system. Zone 3 is situated in the renal parenchyma superior to the collecting system and is also assessed to any tumor that touches the collecting system or touches any component of the renal hilum. Tumors located in each zone are assigned a specific quantitative number depending on the relative difficulty of surgical accessibility, as well as ease of surgical resection and reconstruction. Zone 1 is ascribed the numeric value of 1, zone 2 a numeric value of 2, and zone 3 a numeric value of 3.
The third parameter is based on renal tumor maximal (R)adius (or diameter). This is also assigned a specific value of 1, 2, or 3. Smaller tumors are categorized in lower zones, with a tumor having a diameter < 2.5 cm assigned a numeric value of 1. A renal tumor with a maximal diameter of ≥ 2.5 cm but < 4 cm is given a numeric value of 2. Finally, a tumor with a maximal diameter ≥ 4 cm is assigned a numeric value of 3.
The final measure is the last tumor zone–based variable, which quantifies renal tumor (O)rganization. Much like the RENAL scoring system, it quantifies the risk of complexity of renal surgery based on tumor structure. Again, the renal tumor is classified into zones, with a tumor that has > 50% exophytic growth assigned a low numeric value of 1. A zone 2 tumor would have ≥ 50% endophytic growth but ≤ 75% endophytic growth. These tumors are assigned a numeric value of 2. The third zone of the renal tumor has ≥ 75% endophytic growth based on its predominant location within the renal parenchyma. These tumors are given a numeric value of 3.
The 4 variables are then summed and this number is used to predict overall renal tumor surgical complexity. Tumors are stratified into 3 complexity levels. Low-risk tumors are scored between 4 and 6, whereas intermediate tumors are scored between 7 and 9, and high-risk tumors are scored between 10 and 12.
Before conducting the present study, an institutional retrospective review protocol was finalized and approved, with 200 patients undergoing partial nephrectomy performed by 2 genitourinary surgeons at a tertiary care referral center over a 3-year period (2008-2011). Patients were included in our study cohort if they had undergone NSS for suspicious SRMs of clinical stage T1a or T1b. Both surgeons used an open flank extraperitoneal approach on the inferior border of the 11th rib, with complete renal mobilization and en bloc clamping of the renal artery and vein under warm ischemia (using preclamping mannitol intravenous injection) with reconstruction renorrhaphy and placement of bolsters and sutures. Patients who underwent NSS were excluded if they had a solitary kidney or if they received any other concomitant procedure at the time of the partial nephrectomy. Data points examined included age at diagnosis, partial nephrectomy clamp time, and perioperative complication rate using the Clavien-Dindo system, including urinary leak (fistula) rate, intraoperative blood loss, and pathologic tumor size (maximal diameter). Each renal unit was assigned both a zonal NePhRO score and a RENAL nephrometry score using the same preoperative intravenous contrast-enhanced computed tomographic or magnetic resonance imaging study. All 3 medical professionals reviewing these imaging studies were blinded to their colleagues' findings, and they double checked all their measured scores to ensure data consistency and were timed during scoring. After the data were obtained, both univariate and multivariate Cox regression analyses were conducted ascertaining the prognostic significance of both the zonal NePhRO score and the RENAL nephrometry scoring system with regard to all our respective treatment end points (ie, clamp time, complication rate, urinary leak rate, blood loss, and pathologic tumor size). A P value of < .05 was considered statistically significant.
Of our cohort of 200 patients, the final pathologic examination of the surgical specimens found 3 cases of metanephric adenoma, 4 angiomyolipomas, 5 benign renal cysts, 16 oncocytomas, and 172 RCCs. Overall, 166 patients met our study inclusion criteria. Of these patients, 133 had pathologic stage T1a disease and 33 patients had pathologic stage T1b disease. The mean age at diagnosis was 59.8 years (range, 29-85 years), with the mean tumor diameter on preoperative imaging being 3.1 cm (range, 0.8-6.5 cm). The mean intraoperative blood loss was 293.7 mL (range, 25-2500 mL), and mean warm ischemia clamp time was 19.3 minutes (range, 0-57 minutes). The mean RENAL nephrometry score was 7.21, whereas the mean zonal NePhRO score was 8.62 (Table 1). Of the patients scored using the NePhRO scoring system, 37 patients were categorized in the low-risk category, 84 patients fell into the intermediate-risk category, and 79 patients were high risk (Table 2).
There were a total of 37 perioperative complications using the validated Clavien-Dindo system. The zonal NePhRO score predicted this risk of complication on both univariate and multivariate analyses (P = .0043 and P = .0008, respectively) (Table 3). Of the 37 complications, only 8 patients exhibited urinary leaks (fistulas), which were not statistically correlated with either complexity scoring system. Five patients had local soft tissue cellulitis, which in all cases was managed with a short course of oral antibiotics. Four patients had postoperative renal hemorrhage within the partial nephrectomy surgical bed, but only 1 patient required selective interventional radiologic angioembolization. Three patients had urinary tract infections treated with an oral course of antibiotics, and 3 patients experienced urinary retention during the postoperative period. Three patients had postoperative seromas, and 2 patients had myocardial infarctions, 1 of which required emergent cardiac catheterization with coronary artery stent placement. Two patients had postoperative ileus managed conservatively, and 2 patients had chronic obstructive pulmonary disease exacerbations managed by a brief period of oral steroid administration. The remaining perioperative complications are detailed in Table 4.
Table 3Statistical Analysis Comparing the Prognostic Factors of Perioperative Complications
Univariate Analysis P Value
OR (95% CI)
Multivariate Analysis P Value
OR (95% CI)
Abbreviations: CI = confidence interval; OR = odds ratio.
In addition, tumor pathologic stage and maximal tumor diameter (pathologic) were significantly correlated on univariate analysis with NePhRO scores (P < .0001); however, these did not statistically correlate with the RENAL nephrometry score. On multivariate analysis, however, these variables were not correlated with either the zonal NePhRO or RENAL scoring systems. Of note, the RENAL nephrometry scoring system predicted clamp time better than did the zonal NePhRO scoring system, although this did not achieve statistical significance.
Since the RENAL nephrometry scoring system was first proposed, several subsequent scoring systems (PADUA, DAP, and C-index) have been described. The aim of the present study was to define a simplified numeric scoring system based solely on tumor characteristics and physical attributes of the kidney but also encompassing the key features of the current nephrometry scoring system. We set out to build on the strengths of these previous scoring systems while avoiding their imparted weaknesses, most notably, the difficulties in measuring certain of their variables such as polar lines (RENAL, DAP) and the z-point, which is our self-termed location to describe where lines x and y meet when using the C-index. The creation of a simple zonal scoring system may allow for better interphysician communication and reproducibility.
A major consideration for any standardized scoring system is its reproducibility and the ease with which health care professionals at all levels can be trained. To test our hypothesis that our scoring system was more reproducible and easier for health care professionals to use, we enlisted a physician that was unfamiliar with either scoring system. This physician was trained in the methodologies of the NePhRO and RENAL scoring systems and was then timed while scoring 10 patients from our cohort, using each respective system. The zonal NePhRO scoring system proved to be of greater ease to use (mean time, 15.1 seconds; range, 12.4-17.1 seconds) when compared with the RENAL nephrometry scoring system (mean time, 21.2 seconds; range, 18.3-24.1 seconds).
In addition, when measuring the renal tumor (L) component of the RENAL nephrometry system, the manmade conceptual polar lines demonstrated a concordance rate of 54% among health care professionals.
We, therefore, chose to remove this 1 specific variable from our adapted scoring system (among several other modifications) as a means to simplify it; we also removed any letters from the specific score attributed to a given SRM. Finally, this novel scoring system differs from the RENAL nephrometry scoring system by addressing the fact that SRMs < 4 cm constitute more than a third of such cases and thus may be better suited to smaller diameter scoring parameters.
To further underscore the ease of the zonal NePhRO scoring system and the imparted pitfalls of using the nephrometry scoring system with polar lines, we present a clinical example comparing both the RENAL and zonal NePhRO scoring systems in an individual case.
X is a 47-year-old patient who had a clinical stage T1a SRM and underwent NSS at our institution. Total clamp time was 19 minutes, and the intraoperative estimated blood loss was 600 mL. Preoperatively, the diameter of the tumor on computed tomographic scan was 3.2 cm and was graded by the RENAL nephrometry scoring system as 1 point based on its size. The entirely endophytic nature of the tumor would impart a score of 3 points, and it is < 4 mm from the collecting system, which would therefore constitute an additional 3 points. The tumor being neither anterior nor posterior would assign it the letter “x,” and its location above the polar lines would give it a score of 1 (Fig. 2). In summary, this patient's specific renal tumor, as analyzed by the RENAL nephrometry system, would be given a cumulative score of “8x,” grading this SRM as an intermediate-complexity renal surgical lesion. However, this same tumor would be scored quite differently using the zonal NePhRO scoring system. It would be given 3 points because it touches the collecting system, and being located in physical zone 3 it would be assigned an additional 3 points. Being that it has a diameter of 3.2 cm, it would be given 2 points and being that it has > 75% endophytic growth, it would be given an additional 3 points. This tumor would therefore be given a cumulative score using the zonal NePhRO scoring system of 11 points, making it a high-complexity renal lesion using this scoring system. This patient underwent an open NSS but went on to experience a urine leak postoperatively. This required a subsequent stent placement. Although this constitutes an individual case, we believe this example highlights the ability of the zonal NePhRO to better discriminate between intermediate- and high-complexity renal lesions in terms of their ancillary risks of perioperative surgical complications.
It is evident that the nephrometry scoring system was the first risk stratification model that assigned a complexity score to a surgical renal lesion and hence should be recognized as a major evolution to better characterize these renal lesions before surgical resection. We hope the provided example nicely portrays the inherent flaws of the RENAL nephrometry scoring system, with the use of polar lines and assignment of scores that integrate both numbers and letters to quantify complexity—clearly suboptimally. This case also demonstrates the better accuracy and ease of scoring when using this novel system. It is our realization that the polar line scores are difficult to use for tumors that have endophytic growth and are situated in the upper pole. In the clinical example we have presented, the zonal NePhRO scoring system showed a higher complexity score with corresponding greater risk of perioperative complications, more accurately predicting the specific outcome . We strongly believe that our proposed scoring system encompasses key anatomical features of renal masses that are not captured in other scoring systems.
Our cohort of patients in this study is similar to those evaluated in other studies
in which other renal scoring systems were assessed. The study cohort described by Canter et al appears to be similar to our study population, in which the mean age at diagnosis was 59 years (range, 25-89 years) and the mean tumor diameter was 4.6 cm; 62% of surgically resected lesions were clear cell RCCs. Additionally, their mean RENAL score of 7.49 was similar to our mean RENAL score of 7.21.
Importantly, there are several limitations to the present study that we must highlight. First, our study is limited by the fact that it is retrospective in design, which imparts an inherent selection bias. In addition, this is a single-center study; hence, it requires multicenter study validation. Finally, our new scoring system did not show superiority on multivariate analysis, except in terms of predicting perioperative complications. Hence, this novel scoring system needs further investigation as to its merits when contrasted with other currently described and validated NSS scoring systems, including the C-index, DAP, and PADUA, using a host of definitive surgical outcome end points.
The zonal NePhRO scoring system represents what we believe is the next evolutionary step in the development of novel complexity scoring systems for renal tumor surgery. It draws from the strengths of the RENAL nephrometry scoring system but lacks its inherent manmade polar lines and avoids combining letters and numbers that can result in confusion when scoring end points. Our currently described zonal NePhRO system is simpler, easier to use, and predictive of the risk of perioperative complications. We also suspect it may be more reproducible than the currently available scoring systems, making it a practical tool in clinical research and surgical practice. We invite colleagues around the world to validate our proposed zonal NePhRO scoring system, with the hope that they similarly find high reproducibility, ease of use among health care professionals at various levels of training and, most importantly, clinical utility.
Clinical Practice Points
The development of a universal complexity scoring system is imperative in facilitating interphysician communication, better quantitating risk assessment among patients, and helping characterize the likelihood of perioperative complications.
Currently, there are 4 distinct renal tumor complexity scoring systems that have been proposed to quantify renal tumor characteristics. Although each system intends to identify renal tumor complexity, they do not all measure the same characteristics of the tumor with regard to its anatomical relationship to the renal unit. Each system has its inherent strengths and weaknesses.
We strived to create a simplified numeric scoring system based solely on tumor characteristics and physical attributes of the kidney, encompassing the key features of the current nephrometry scoring systems but eliminating their inherent weaknesses.
The zonal NePhRO score predicted the risk of complication on both univariate and multivariate analyses in our study cohort. In addition, tumor pathologic stage and maximal tumor diameter (pathologic) were significantly correlated on univariate analysis with NePhRO scores; however, these did not statistically correlate with the RENAL nephrometry score.
The zonal NePhRO scoring system represents what we believe is the next evolutionary step in the development of novel complexity scoring systems for renal tumor surgery. We suspect it may be more reproducible than the currently available scoring systems, making it a practical tool in clinical research and surgical practice.
The authors have stated that they have no conflicts of interest.
The authors would like to thank Nicholas Gould for the development of the diagrams detailing our zonal NePhRO scoring system. His medical graphic talents were greatly beneficial to our work.
The R.E.N.A.L. nephrometry score: a comprehensive standardized system for quantitating renal tumor size, location and depth.