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Keywords:

  • kidney neoplasms;
  • pathology;
  • radiography;
  • retrospective study;
  • CT

Abstract

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. PATIENTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. CONFLICT OF INTEREST
  8. REFERENCES

OBJECTIVE

To evaluate the difference between radiographic size on computed tomography (CT) and the pathological size of renal tumours, in contemporary patients.

PATIENTS AND METHODS

We retrospectively reviewed the records of 521 patients undergoing surgical resection of a renal mass between 2000 and 2007, who had tumour sizes recorded from both preoperative CT and pathological evaluation of the tumour specimen. Data on histological tumour type were also extracted. The paired Student’s t-test was used to compare the mean radiographic size as measured on CT with the mean pathological size, with P < 0.05 considered to indicate statistical significance.

RESULTS

For all patients, the mean radiographic size and mean pathological size was 4.79 and 4.69 cm, respectively (P = 0.02). Therefore, on average, radiographic size overestimated pathological size by 1 mm. In patients with a tumour of 4–7 cm, radiographic size overestimated pathological size by 0.21 cm (P = 0.007). However, there was no significant difference in patients with a tumour of <4 cm or >7 cm.

CONCLUSIONS

Using contemporary patients, there was a statistically significant overestimation of renal tumour sizes by CT compared with the pathological assessment. However, the overall difference between radiographic and pathological tumour size was 1 mm, suggesting that CT provides an accurate method with which to estimate renal tumour size.


Abbreviations
PN

partial nephrectomy

RN

radical nephrectomy.

INTRODUCTION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. PATIENTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. CONFLICT OF INTEREST
  8. REFERENCES

Tumour size has substantial clinical implications for patients with a renal mass. Knowing the tumour size permits proper staging, facilitates a discussion of prognosis, and guides treatment strategy, specifically the choice between radical nephrectomy (RN), partial nephrectomy (PN) and observation. However, in current reports tumour size is largely represented by pathological size, which is routinely recorded during pathological sectioning [1,2]. Thus, when counselling patients before surgery the physician must assume that radiographic size is equivalent to pathological size when addressing the expected outcome and specifically when making recommendations for therapy (i.e. PN vs RN).

Several previous observations suggest that there is an overestimation of the pathological size of renal tumours when compared with radiographic size [3–5]. Thus, if a specific size threshold (largely determined by the pathological size in most published series) is used to identify patients for PN [6–8], radiographic overestimation might diminish the number of patients who would otherwise be candidates for a nephron-sparing approach [4]. However, most reports addressing this issue are limited by including few patients and used older imaging techniques [3,4]. We examined a contemporary group of patients to determine if radiographic size overestimates pathological size of renal tumours, and if so, by how much.

PATIENTS AND METHODS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. PATIENTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. CONFLICT OF INTEREST
  8. REFERENCES

Upon approval from the institutional review board, we identified 561 patients in the Memorial Sloan-Kettering Cancer Center kidney cancer database who were treated surgically for a renal cortical tumour and who had both pathological and radiographic (CT) tumour sizes available. This database is prospectively maintained and includes >150 variables for each patient, including radiographic and pathological tumour size. Of these patients, 40 were excluded due to preoperative CT obtained >4 months before surgery. Among the remaining 521 patients, 27 (6%) had multifocal tumours. For these patients, the largest tumour diameter on CT and pathological size was used for comparison. Patient demographics, including age, sex, histology, type of procedure and cancer stage, were collected from our database, and are detailed in Table 1.

Table 1.  The demographic data
FeatureMedian or n (%)
  • *

    Provided for 454 patients with RCC.

Age, years 61 (51–69)
Sex
 Male328 (63)
 Female193 (37)
Type of procedure
 Laparoscopic PN 58 (11)
 Laparoscopic RN 31 (6)
 PN271 (52)
 RN161 (31)
Histology
 Clear cell309 (59)
 Papillary 56 (11)
 Chromophobe 56 (11)
 RCC other 33 (6)
 Oncocytoma 45 (9)
 Angiomyolipoma 12 (2)
 Benign other 10 (2)
Primary tumour classification*
 T1a224 (49)
 T1b 72 (16)
 T2 28 (6)
 T3a 66 (15)
 T3b 61 (13)
 T4  3 (<1)

The histological subtypes of each tumour were taken from the official pathological report and categorized as clear cell, papillary, chromophobe, RCC other, oncocytoma, angiomyolipoma, or benign other. The paired Student’s t-test was used to compare the mean CT size with mean pathological size, with P < 0.05 considered to indicate statistically significant differences.

RESULTS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. PATIENTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. CONFLICT OF INTEREST
  8. REFERENCES

A summary of patient demographics is detailed in Table 1 and a scatter plot of radiographic and pathological size shown in Fig. 1. The patients included 193 (37%) women and 328 (63%) men, with an overall median (range) age of 61 (51–69) years. Among the 521 patients, 329 (63%) had a PN and 192 (37%) a RN. Among the 329 patients treated with PN the mean (sd) size on CT was 3.31 (1.49) and the mean pathological size was 3.11 (1.53) (P < 0.001). There was no significant difference in mean size on CT, of 7.34 (3.35) cm, and mean pathological size, of 7.38 (3.63) cm, for patients treated with RN (P = 0.7).

image

Figure 1. A scatter plot of CT and pathological estimates of tumour size. For reference, the line of perfect correlation is shown.

Download figure to PowerPoint

The mean size on CT and mean pathological size for all 521 patients was 4.79 and 4.69 cm, respectively. The mean difference in size for all tumours examined was 0.10 cm larger in the CT assessment than in the pathological measurement (P = 0.02). All 521 patients with renal tumours had a median difference in size (interquartile range) of 0.20 (−0.30, 0.60) with the maximum negative difference of −5.10 and maximum positive difference of 4.4.

Table 2 lists the mean CT and pathological tumour sizes separated into 1-cm intervals by CT size. There were statistically significant overestimates in renal tumour size by CT in the 2–<5 cm range. The largest difference in radiographic size vs pathological size was in the 4–<5 cm CT size category, with an overestimate of 0.32 cm (P = 0.004). The only underestimate by CT was in the 1–<2 cm range, where the pathological size was 0.24 cm larger than the CT size (P = 0.02).

Table 2.  The mean CT and pathological estimates of tumour size by 1 cm CT categories, clinical size stages and histological subtype
CategorynMean (sd) estimate byMean difference (95% CI)P
CTPathology
CT estimate, cm
 <110.6 (–)1.4 (–)  0.8 (–)
 1 to <2631.51 (0.27)1.75 (0.76)  0.24 (0.05, 0.42)0.020
 2 to <3902.42 (0.28)2.28 (0.55)−0.14 (−0.25, −0.03)0.010
 3 to <41093.44 (0.30)3.27 (0.90)−0.17 (−0.34, −0.01)0.050
 4 to <5714.38 (0.31)4.06 (0.93)−0.32 (−0.54, −0.11)0.004
 5 to <6585.40 (0.29)5.18 (1.13)−0.21 (−0.48, 0.06)0.100
 6 to <7336.36 (0.34)6.36 (1.30)  0 (−0.44, 0.44)1
 ≥79610.14 (2.43)10.09 (3.10)−0.05 (−0.38, 0.28)0.800
 Total5214.79 (3.06)4.69 (3.25)−0.10 (−0.20, −0.02)0.020
CT clinical size, cm
 <42632.62 (0.83)2.56 (0.99)−0.06 (−0.15, 0.03)0.200
 4–71665.19 (0.86)4.98 (1.41)−0.21 (−0.37, −0.06)0.007
 >79210.28 (2.39)10.23 (3.10)−0.05 (−0.39, 0.29)0.700
 Total5214.79 (3.06)4.69 (3.25)−0.10 (−0.20, −0.02)0.020
Histological subtype
 Clear cell3094.944.71−0.23<0.001
 Papillary564.364.72  0.370.020
 Chromophobe565.685.62−0.050.700
 RCC other334.714.83  0.120.500
 Oncocytoma453.753.66−0.100.500
 Angiomyolipoma124.23.86−0.340.200
 Benign other103.253.54  0.290.400

Table 2 also lists the mean CT and pathological tumour sizes divided into clinically significant ranges of <4, 4–7 and >7 cm. In patients with a tumour of 4–7 cm the CT size was an overestimate vs the pathological size, of 0.21 cm (P = 0.007). However, there was no significant difference in patients with tumours of <4 or >7 cm. Among 258 patients with a CT size of >4 cm and thought to have a ≥T1b tumour, 30 (11.6%) had a final pathologic size of <4 cm. Among 92 patients with a CT size of >7 cm and thought to have a ≥T2 tumour, seven (7.6%) had a final pathological size of <7 cm.

Table 2 also shows a comparison of histological subtypes of renal tumours and the difference in size between mean CT and pathological size. Among the 309 patients with clear cell histology, tumour size was overestimated by 0.23 cm on CT (P < 0.001). Among the 56 patients who had papillary renal tumours the CT size was underestimated by 0.37 cm (P = 0.02). In the remaining histological subgroups there was no significant difference between the CT and pathological tumour sizes.

DISCUSSION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. PATIENTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. CONFLICT OF INTEREST
  8. REFERENCES

To our knowledge, we present the largest comparison of radiographic and pathological tumour sizes for patients with a renal mass. Consistent with previous observations, CT overestimated the pathological size when comparing all patients, but the overall difference between the CT and pathological estimates was only 1 mm. While it was statistically significant we do not think that 1 mm represents a clinically significant difference in tumour size. Thus, we consider that our data confirm that contemporary CT imaging adequately estimates the true tumour size. This information should prove useful when counselling patients about the risk of metastases and when deciding on an appropriate operative approach.

When evaluating the subgroups according to 1-cm intervals, the largest differences in size were in patients with tumours of <5 cm. Interestingly, patients with tumours estimated on CT as <2 cm tended to have pathological tumours that were significantly larger. However, the difference in size for these patients was slightly more than 2 mm, which we argue is a clinically insignificant artefact. The largest overestimate for CT was in patients with tumours of 4–5 cm. This difference, while statistically significant, was again only 3 mm and probably only significant because there were so many patients. Differences in CT and pathological tumour size were less pronounced for patients with larger tumours. Indeed, the CT size and pathological size for patients with tumours of 6–7 cm were identical (mean 6.36 cm for both). This observation is in agreement with Schlomer et al.[4], who observed similar trends in their cohort of 126 patients.

Tumour size is an important clinical and pathological feature for evaluating patients with RCC. For tumours limited to the kidney, the pT1a, pT1b and pT2 primary classifications are determined solely by tumour size [9]. In the present study, of the 258 patients with a CT estimate of >4 cm and thought to have a ≥T1b tumour, 30 had a final pathological size of <4 cm. A similar effect was found among the 92 patients with a CT estimate of >7 cm and thought to have ≥T2 tumour; seven had a final pathological size of <7 cm. Although this discrepancy in tumour stage might seem to have an effect on patient selection for different treatments, we think that this was true for only a few patients and therefore would not change the overall management.

Tumour size is an independent predictor of progression-free survival and cancer-specific survival after surgery [10]. Furthermore, tumour size has largely been used when recommending PN for patients in an elective situation. Traditionally, a 4-cm threshold has been proposed [6], although more recent observations suggest that a threshold of 7 cm for appropriately selected patients is safe [7,8]. Thus, tumour size is widely used and represents a key factor to dictate therapy for patients with RCC.

Another important prognostic indicator, that might also have a role in deciding treatment, is the histopathological features of RCC. Because >30% of patients have renal tumours with histology other than conventional clear cell carcinoma, studies have assessed the correlation between size, histology and metastatic potential [11,12]. Tumours of histology other than clear cell carcinoma appear to have a better prognosis and might be suitable for PN regardless of size [13,14]. We evaluated the difference between mean CT tumour size and mean pathological size within each histological subgroup. There were statistically significant differences in the clear cell and papillary types, but the difference were small (2–3 mm) and unlikely to be clinically significant. With the current focus on nephron-sparing surgery for renal masses, we anticipate that tumour size will have an expanded role in the preoperative management of patients with a renal mass.

With the increased frequency of cross-sectional imaging, small and incidental renal masses are being diagnosed more often than in the past [15,16]. Thus, more patients, especially those with significant medical comorbidities, are being considered for observation [17]. In addition, chronic renal failure is more prevalent than previously thought among patients with a renal mass [18]. More than 25% of all patients with a renal mass have at least Grade 3 chronic kidney disease at presentation [18]. Furthermore, a recent retrospective observation suggested that PN is associated with a better overall survival for patients with small renal masses than RN [19]. Thus, we anticipate that PN will be used more often.

Our data suggest that while CT might overestimate the true tumour size, this overestimate is unlikely to be of clinical importance. While evaluation within the histological subgroups showed significant differences between the CT and pathological sizes in clear cell and papillary tumours, these variations were again small. We think that this study confirms the accuracy of CT for establishing the size of renal masses.

The present study has several limitations; our review was a retrospective, single-institution analysis of patients and is subject to the biases that surround these study types. Further bias might result from routine pathological processing with formalin fixation, a process that has been shown to reduce tumour volume [20]. Another important weakness is that there was no central review of the radiographic studies.

In conclusion, using a contemporary cohort of patients, there was a statistically significant overestimation of renal tumour sizes when comparing CT with pathology. However, the overall difference for tumours was 1 mm, which suggests that CT estimates renal tumour size in a manner that is adequate for clinical decision-making.

REFERENCES

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. PATIENTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. CONFLICT OF INTEREST
  8. REFERENCES