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ing [10, 11]. Although there are other report-ed renal tumor methodologies, such as the PADUA (preoperative aspects and dimen-sions used for anatomic [classification]) and CI (centrality index) systems, the nephrom-etry 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 peri-operative information used to predict long-term outcomes and is increasingly being in-corporated into clinical trials similar to the Response Evaluation Criteria in Solid Tu-mors guidelines (RECIST) [14]. Because of its increasing use, it is important that radiolo-gists have an understanding of how to calcu-late the nephrometry score and include this number in diagnostic reports.

Materials and MethodsThe nephrometry scoring system was devel-

oped using images obtained from MDCT, al-though MRI can also be used. Contrast-enhanced imaging is recommended. If contrast administra-tion is contraindicated, unenhanced MRI can be used to assign the nephrometry score. Our stan-dard CT protocol consists of a three-phase exam-ination that includes unenhanced, nephrographic phase, and excretory phase imaging. Nephro-graphic phase imaging occurs at approximate-ly 100 seconds and excretory phase imaging at 5 minutes after contrast administration. The scan-ning 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.

RENAL Nephrometry Scoring System: The Radiologists Perspective

Rosaleen B. Parsons1 Daniel Canter2 Alexander Kutikov3 Robert G. Uzzo3

Parsons RB, Canter D, Kutikov A, Uzzo RG

1Department of Diagnostic Imaging, Fox Chase Cancer Center, 333 Cottman Ave, Philadelphia, PA 19111. Address correspondence to R. B. Parsons (rosaleen.parsons@fccc.edu).

2Department of Urology, Emory University, Atlanta, GA.

3Department of Urology, Fox Chase Cancer Center, Philadelphia, PA.

Genitour inar y Imaging Cl in ica l Perspect ive

WEB This is a Web exclusive article.

AJR 2012; 199:W355W359

0361803X/12/1993W355

American Roentgen Ray Society

The incidence of renal cell carci-noma (RCC) continues to rise because of the widespread use of cross-sectional imaging [1], with

the greatest increase noted in renal tumors sized 24 cm [2]. Most new cases of local-ized RCC are detected incidentally as an en-hancing renal mass on cross-sectional imag-ing [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 ei-ther partial or total nephrectomy results in a 99.2% recurrence-free survival rate [5].

The incidence of partial nephrectomies continues to increase. In 2005, approximate-ly 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 re-nal mass remains overly subjective because of provider and patient biases, precluding meaningful comparisons between studies due to the lack of standardized and quanti-fiable tumor descriptors. The RENAL (ra-dius, exophytic/endophytic properties, near-ness of tumor to the collecting system or sinus in millimeters, anterior/posterior lo-cation 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 re-cently introduced LI-RADS for liver imag-

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.

OBJECTIVE. The nephrometry score, which is determined from cross-sectional imag-ing, 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 con-tribute 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.

Parsons et al.Nephrometry Score

Genitourinary ImagingClinical Perspective

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ResultsThe RENAL nephrometry score is based on

the five most reproducible features that char-acterize the anatomy of a solid renal mass on contrast-enhanced cross-sectional imaging [9]. The features are referred to as (R) radius (tu-mor size as maximal diameter), (E) exophytic/endophytic properties of the tumor, (N) near-ness 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 as-signed to the tumor if an anterior or posterior designation is not possible. An additional suf-fix 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 13 (Table 1).

Imaging ClassificationThe R descriptor represents the maximum

diameter of the mass. A radius of 4 cm differen-tiates a T1a lesion from a T1b lesion and, until

recently, was considered the maximum dimen-sion for partial nephrectomy. Lesions 4 cm are assigned 1 point, those > 4 but < 7 cm are assigned 2 points, and those 7 cm are as-signed 3 points.

The E descriptor denotes the exophyt-ic or endophytic location of the tumor. Le-sions that are predominately endophytic pose

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. 13).

The N descriptor denotes the proximity to the collecting system measured in millimeters

TABLE 1: RENAL Nephrometry Scoring System

Component

Score

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

NoteSee Figure 7 for further explanation of L component.

Fig. 145-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.

Fig. 263-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.

Fig. 373-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.

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and is best determined on excretory images. As with the R descriptor, the point scale is di-vided between values of 4 and 7 using millime-ters rather than centimeters. Tumors again are divided into three categories: 7 mm or great-er 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 as-signed a point value. The a/p descriptor is determined from axial imaging. If the tumor lies primarily on the ventral surface of the

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 le-sion, 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 de-termined 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 as-signed (Fig. 7). Lesions that abut the main renal vein or artery are given the suffix h to define the hilar location. This h designa-tion does not impact the point scale.

The Nephrometry Score GradingUsing the scoring system, tumor complex-

ity is determined: low complexity (nephrome-try score = 46), moderate complexity (neph-rometry score = 79), and high complexity (nephrometry score = 1012) (Figs. 810).

Fig. 438-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.

Fig. 558-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. 652-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. 7Assigning 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.

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physicians that persisted when the house staff and the medical student were included. The highest concordance was with the R desig-nation, and the N component, which mea-sures the distance of the tumor from the col-lecting system, had the lowest concordance. The authors concluded that assigning a neph-rometry score was reliable and required min-imal 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 ne-phrectomy are difficult to compare because of the subjectivity of preoperatively determining surgical complexity. The reported complica-tion rates for open laparoscopic or robotically assisted partial nephrectomy range from 4.5% to 10.6% [5]. Patients with a low-complexi-ty nephrometry score are less likely to expe-rience 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 post-operative urologic complication. A higher nephrometry score has been shown to corre-late with ischemia time during partial nephrec-tomy 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,

DiscussionPerforming a partial nephrectomy is techni-

cally challenging. For stage I tumors, the out-comes have been shown to be equivalent for par-tial 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 chron-ic kidney disease, in particular cardiovascular diseases [18]. Partial nephrectomy prevents fu-ture reduction of renal function compared with matched patients undergoing radical or total ne-phrectomy [19, 20]. Despite these data, partial nephrectomy remains underutilized. Data pub-lished 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].

Cross-sectional imaging is crucial in the preoperative planning for management of a re-nal mass. The decision to perform a partial ne-phrectomy is subjective, and, before the devel-opment of the nephrometry score, there was no standard method to score renal mass com-plexity. The five featuresR (radius), E (exo-phytic/endophytic), N (nearness), A (anteri-or), 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 be-come more common in urologic practice. In one retrospective study of 95 patients, six re-viewers, including staff urologists, radiolo-gists, house staff, and one medical student, independently assigned a nephrometry score after reviewing the instructions from the Nephrometry Website [22]. The authors re-ported substantial agreement among the three

A

Fig. 949-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

A

Fig. 858-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.

B

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and death from renal cell carcinoma [22]. Al-though the numbers were small, the data suggest that the anatomic features described in the neph-rometry score may predict metastatic potential.

Radiologists are familiar with the RECIST criteria, and nephrometry scores are beginning to be incorporated into clinical trial measure-ments. In one recent study, patients with un-resectable renal cell carcinoma were treated with neoadjuvant sunitinib and were assigned a RENAL nephrometry score. At baseline, 81% of tumors were categorized as high complex-ity and 46% were downgraded to moderately complex after treatment, which facilitated sur-gery. Decrease in the tumor proximity to the central hilar structures was the main parame-ter that reduced the nephrometry score and de-creased the surgical complexity [26].

In conclusion, the RENAL nephrometry scoring system provides an easy methodolo-gy to stratify the complexity of renal tumors, aiding in treatment decision making and coun-seling as well as providing a platform for stan-dardized 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 duplica-tion, are not included in the scoring system, and as nephrometry becomes more widely adopted, modifications might become neces-sary. 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.

AcknowledgmentWe thank Maryann Krajkowski for editorial

assistance in the preparation of the manuscript.

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Fig. 1061-year-old man with high-complexity left clear cell carcinoma (arrow). Nephrometry score is 2 + 2 + 3 + a + 3 = 10a.

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