RENAL Nephrometry Scoring System: The Radiologist s Perspective

Genitourinary Imaging Clinical Perspective Parsons et al. Nephrometry Score Genitourinary Imaging Clinical Perspective Rosaleen B. Parsons 1 Daniel Canter 2 Alexander Kutikov 3 Robert G. Uzzo 3 Parsons RB, Canter D, Kutikov A, Uzzo RG Keywords: nephron-sparing surgery, renal cell carcinoma, standardized reporting DOI:10.2214/AJR.11.8355 Received December 2, 2011; accepted after revision January 20, 2012. 1 Department of Diagnostic Imaging, Fox Chase Cancer Center, 333 Cottman Ave, Philadelphia, PA 19111. Address correspondence to R. B. Parsons (rosaleen.parsons@fccc.edu). 2 Department of Urology, Emory University, Atlanta, GA. 3 Department of Urology, Fox Chase Cancer Center, Philadelphia, PA. WEB This is a Web exclusive article. AJR 2012; 199:W355 W359 0361 803X/12/1993 W355 American Roentgen Ray Society RENAL Nephrometry Scoring System: The Radiologist s Perspective OBJECTIVE. The nephrometry score, which is determined from cross-sectional imaging, stratifies renal masses into low, intermediate, and high complexity. The purpose of this article is to understand how the score is determined and review the five key features that contribute to the nephrometry score. CONCLUSION. The scoring system has implications for surgical planning and has been widely adopted by urologists but is less familiar to radiologists. T he incidence of renal cell carcinoma (RCC) continues to rise because of the widespread use of cross-sectional imaging [1], with the greatest increase noted in renal tumors sized 2 4 cm [2]. Most new cases of localized RCC are detected incidentally as an enhancing renal mass on cross-sectional imaging [3]. In 2010, the estimated 58,240 new cases of renal tumors accounted for 4% and 3% of new cancer cases in men and women, respectively [4]. Surgical management of either partial or total nephrectomy results in a 99.2% recurrence-free survival rate [5]. The incidence of partial nephrectomies continues to increase. In 2005, approximately 27% of patients with tumors less than 4 cm underwent partial nephrectomy, with the majority undergoing total nephrectomy [6]. More recent data indicate that greater than 65% of patients with tumors less than 4 cm undergo partial nephrectomy [7, 8]. To date, treatment decision making for a given renal mass remains overly subjective because of provider and patient biases, precluding meaningful comparisons between studies due to the lack of standardized and quantifiable tumor descriptors. The RENAL (radius, exophytic/endophytic properties, nearness of tumor to the collecting system or sinus in millimeters, anterior/posterior location relative to polar lines) nephrometry scoring system was recently introduced as an objective reproducible means to describe salient renal tumor anatomy [9], similar to BI-RADS used in breast imaging and the recently introduced LI-RADS for liver imag- ing [10, 11]. Although there are other reported renal tumor methodologies, such as the PADUA (preoperative aspects and dimensions used for anatomic [classification]) and CI (centrality index) systems, the nephrometry score is the first objective system that quantifies the complexity of the renal tumor [12, 13]. Since its introduction, the RENAL nephrometry scoring system has been shown to provide important preoperative and perioperative information used to predict longterm outcomes and is increasingly being incorporated into clinical trials similar to the Response Evaluation Criteria in Solid Tumors guidelines (RECIST) [14]. Because of its increasing use, it is important that radiologists have an understanding of how to calculate the nephrometry score and include this number in diagnostic reports. Materials and Methods The nephrometry scoring system was developed using images obtained from MDCT, although MRI can also be used. Contrast-enhanced imaging is recommended. If contrast administration is contraindicated, unenhanced MRI can be used to assign the nephrometry score. Our standard CT protocol consists of a three-phase examination that includes unenhanced, nephrographic phase, and excretory phase imaging. Nephrographic phase imaging occurs at approximately 100 seconds and excretory phase imaging at 5 minutes after contrast administration. The scanning parameters are as follows: 240 mas and 120 kvp; slice thickness, 5 mm; increment, 5 mm; and pitch, 0.8. Coronal and sagittal reconstructions are obtained with 1.5 0.8 mm thickness. W355

Parsons et al. TABLE 1: RENAL Nephrometry Scoring System Score Component Results The RENAL nephrometry score is based on the five most reproducible features that characterize the anatomy of a solid renal mass on contrast-enhanced cross-sectional imaging [9]. The features are referred to as (R) radius (tumor size as maximal diameter), (E) exophytic/ endophytic properties of the tumor, (N) nearness of the deepest portion of the tumor to the collecting system or renal sinus, (A) anterior (a)/posterior (p) descriptor, and the (L) location relative to the polar line. 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 if the tumor abuts the main renal artery or vein. All components except for the (A) descriptor are scored on a scale of 1 3 (Table 1). 1 Point 2 Points 3 Points R (radius, maximal diameter) (cm) 4 > 4 but < 7 7 E (exophytic/endophytic) 50 % exophytic < 50% exophytic Completely endophytic N (nearness to collecting system/renal sinus) (mm) 7 > 4 but < 7 4 A (anterior/posterior locator) No points given. Descriptor of a, p, or x assigned to describe mass location. L (location relative to polar lines) Entirely below lower polar or above upper polar line Mass crosses polar line 50% of mass is across polar line or mass is entirely between polar lines or mass crosses axial midline Note See Figure 7 for further explanation of L component. Fig. 1 45-year-old woman with 3-cm right clear cell renal cancer (arrow). Solid line shows expected renal contour used to determine E exophytic/endophytic attribute. Tumor projects more than 50% outside renal cortex and should be assigned E score of 1. Nephrometry score is 1 + 1 + 1 + a + 1 = 4a. recently, was considered the maximum dimension for partial nephrectomy. Lesions 4 cm are assigned 1 point, those > 4 but < 7 cm are assigned 2 points, and those 7 cm are assigned 3 points. The E descriptor denotes the exophytic or endophytic location of the tumor. Lesions that are predominately endophytic pose Fig. 2 63-year-old man with small clear carcinoma of right kidney (arrow) that is < 50% exophytic with E score of 2. Nephrometry score is 1 + 2 + 1 + p + 1 = 5p. Solid line shows expected renal contour used to determine E exophytic/ endophytic attribute of nephrometry score. a greater surgical challenge than those that are exophytic. Lesions that project more than 50% outside the renal cortex are assigned 1 point, those less than 50% are assigned 2 points, and those that are entirely endophytic are assigned 3 points (Figs. 1 3). The N descriptor denotes the proximity to the collecting system measured in millimeters Imaging Classification The R descriptor represents the maximum diameter of the mass. A radius of 4 cm differentiates a T1a lesion from a T1b lesion and, until Fig. 3 73-year-old man with centrally located clear cell renal carcinoma (arrow). Nephrometry score is 2 + 3 + 3 + x + 3 = 11x; x denotes central location. E score is 3. W356

Nephrometry Score and is best determined on excretory images. As with the R descriptor, the point scale is divided between values of 4 and 7 using millimeters rather than centimeters. Tumors again are divided into three categories: 7 mm or greater from the collecting system or renal sinus (1 point), tumors > 4 but < 7 mm (2 points), and tumors 4 mm or less from the central collecting system (3 points) (Figs. 4 and 5). The A descriptor indicates the anterior or posterior location of the tumor and is not assigned a point value. The a/p descriptor is determined from axial imaging. If the tumor lies primarily on the ventral surface of the Fig. 4 38-year-old man with small right papillary renal cell cancer (arrow) that is > 5 mm from collecting system. Nephrometry score is 1 + 2 + 2 + p + 1 = 6p. N score is 1. kidney the anterior (a) descriptor is assigned. Tumors located on the dorsal renal surface are assigned a posterior (p) designation. Tumors that do not fall into one of these categories, such as a purely lateral or a central apical lesion, are assigned the designation x (Fig. 6). The L descriptor defines the location of the tumor with respect to the polar lines. The superior and inferior polar lines are defined by the renal vascular pedicle and can be determined on either axial or coronal images. Tumors that sit entirely above or below the polar boundaries are assigned a score of 1; if the lesion crosses the polar line, a score of 2 is assigned; and if > 50% of the mass crosses the polar line or the mass is located entirely between the polar lines, as score of 3 is assigned (Fig. 7). Lesions that abut the main renal vein or artery are given the suffix h to define the hilar location. This h designation does not impact the point scale. The Nephrometry Score Grading Using the scoring system, tumor complexity is determined: low complexity (nephrometry score = 4 6), moderate complexity (nephrometry score = 7 9), and high complexity (nephrometry score = 10 12) (Figs. 8 10). Fig. 5 58-year-old man with central clear cell carcinoma (arrow) that is less than 4 mm from collecting system. N score is 3. Nephrometry score is 1 + 3 + 3 + p + 3 = 10p. Fig. 6 52-year-old man with centrally located clear cell renal cancer (arrow) with both x and h attributes: x because it is central apical tumor and h because it touches main renal vasculature. Suffix x is assigned to tumor if anterior or posterior designation is not possible. Additional suffix h is used to designate hilar location if tumor abuts main renal artery or vein. Nephrometry score is 2 + 2 + 3 + x + 2h = 9xh. Fig. 7 Assigning location (L) score. Blue lines delineate polar lines. In image 1, L = 1 because masses are above or below polar lines. In image 2, L = 2 because masses cross polar lines. In image 3, L = 3 because mass a crosses polar line > 50%; b is located between polar lines; and c crosses axial midline. W357

Parsons et al. Fig. 8 58-year-old man with papillary renal cancer. A and B, Axial (A) and coronal (B) CT images show low-complexity cancer (arrow), Nephrometry score is 1 + 1 + 1 + p + 1 = 4p. Discussion Performing a partial nephrectomy is technically challenging. For stage I tumors, the outcomes have been shown to be equivalent for partial and radical nephrectomy [15, 16]. After total nephrectomy, the incidence of chronic kidney disease is high [17], and emerging data report long-term deleterious health effects from chronic kidney disease, in particular cardiovascular diseases [18]. Partial nephrectomy prevents future reduction of renal function compared with matched patients undergoing radical or total nephrectomy [19, 20]. Despite these data, partial nephrectomy remains underutilized. Data published recently report that approximately 27% of all patients with localized renal masses are treated with nephron-sparing surgery regardless of anatomic features [6]. In one study, the rate of partial nephrectomy for lesions less than 4.0 cm increased to 40%; however, many would argue that this rate is still too low [21]. A Cross-sectional imaging is crucial in the preoperative planning for management of a renal mass. The decision to perform a partial nephrectomy is subjective, and, before the development of the nephrometry score, there was no standard method to score renal mass complexity. The five features R (radius), E (exophytic/endophytic), N (nearness), A (anterior), L (location) capture the key anatomic elements of the renal mass that in turn can be used to rank the surgical complexity into low, intermediate, and high categories. Assigning a nephrometry score has become more common in urologic practice. In one retrospective study of 95 patients, six reviewers, including staff urologists, radiologists, house staff, and one medical student, independently assigned a nephrometry score after reviewing the instructions from the Nephrometry Website [22]. The authors reported substantial agreement among the three B physicians that persisted when the house staff and the medical student were included. The highest concordance was with the R designation, and the N component, which measures the distance of the tumor from the collecting system, had the lowest concordance. The authors concluded that assigning a nephrometry score was reliable and required minimal training. In another recently published article, the L component was reported as the most challenging of the five components to reliably score [23]. The complication rates from partial nephrectomy are difficult to compare because of the subjectivity of preoperatively determining surgical complexity. The reported complication rates for open laparoscopic or robotically assisted partial nephrectomy range from 4.5% to 10.6% [5]. Patients with a low-complexity nephrometry score are less likely to experience a postoperative bleed or urinary fistula compared with moderate-complexity masses, whereas lesions with scores between 12 and 14 were five times more likely to have a postoperative urologic complication. A higher nephrometry score has been shown to correlate with ischemia time during partial nephrectomy and greater likelihood of developing a postoperative urinary fistula [24, 25]. In addition to greater surgical complications, higher nephrometry scores have been shown to correlate with pathologic stage, nuclear grade, A Fig. 9 49-year-old woman with clear cell carcinoma. A and B, Axial (A) and coronal (B) CT images show moderately complex right renal cancer (arrow). Nephrometry score is 1 + 1 + 3 + a + 2h = 7ah; h is assigned because tumor touches central vascular structures. B W358

Nephrometry Score Fig. 10 61-year-old man with high-complexity left clear cell carcinoma (arrow). Nephrometry score is 2 + 2 + 3 + a + 3 = 10a. 13. Simmons MN, Ching CB, Samplaski MK, et al. Kidney tumor location measurement using the C index method. J Urol 2010; 183:1708 1713 14. Therasse P, Arbuck SG, Eisenhauer EA, et al. New guidelines to evaluate the response to treatment in solid tumors: European Organization for Research and death from renal cell carcinoma [22]. Although the numbers were small, the data suggest that the anatomic features described in the nephrometry score may predict metastatic potential. Radiologists are familiar with the RECIST criteria, and nephrometry scores are beginning to be incorporated into clinical trial measurements. In one recent study, patients with unresectable renal cell carcinoma were treated with neoadjuvant sunitinib and were assigned a RENAL nephrometry score. At baseline, 81% of tumors were categorized as high complexity and 46% were downgraded to moderately complex after treatment, which facilitated surgery. Decrease in the tumor proximity to the central hilar structures was the main parameter that reduced the nephrometry score and decreased the surgical complexity [26]. In conclusion, the RENAL nephrometry scoring system provides an easy methodology to stratify the complexity of renal tumors, aiding in treatment decision making and counseling as well as providing a platform for standardized academic reporting. Although the data are preliminary, the nephrometry score appears to correlate with long-term outcomes. Renal abnormalities that might contribute to surgical morbidity, such as fusion or duplication, are not included in the scoring system, and as nephrometry becomes more widely adopted, modifications might become necessary. The interpreting radiologists will find that assigning a nephrometry score is simple, and doing so will ensure that the salient features of a renal carcinoma are reported for operative planning. The scoring system can be found on the Internet at www.nephrometry.com. Acknowledgment We thank Maryann Krajkowski for editorial assistance in the preparation of the manuscript. References 1. Chow WH, Devesa SS, Warren JL, Fraumeni JF Jr. Rising incidence of renal cell cancer in the United States. JAMA 1999; 281:1628 1631 2. Hollingsworth JM, Miller DC, Daignault S, Hollenbeck BJ. Rising incidence of small renal masses: a need to reassess treatment effect. J Natl Cancer Inst 2006; 98:1331 1334 3. Parsons JK, Schoenberg MS, Carter HB. Incidental renal tumors: casting doubt on the efficacy of early intervention. Urology 2001; 57:1013 1015 4. Jemal A, Siegel R, Xu J, Ward E. Cancer statistics. CA Cancer J Clin 2010; 60:277 300 5. Campbell SC, Novick AC, Belldegrun A, et al. 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