Size Measurement and T-staging of Lung Adenocarcinomas Manifesting as Solid Nodules ≤30 mm on CT

Rationale and Objectives

This study aimed to compare long-axis diameter to average computed tomography (CT) diameter measurements of lung adenocarcinomas manifesting as solid lung nodules ≤30 mm on CT, as referenced to pathologic measurements, and to determine the impact of the two CT measurement approaches on tumor (T)-staging of nodules.

Materials and Methods

This institutional review board-approved study included all 274 radiologic solid adenocarcinomas resected at our institution over 10 years. Two observers measured long- and short-axis diameters on pre-resection chest CT in lung and mediastinal windows. T-stages were determined. CT measurements and T-stages were compared to pathology measurements and T-stages using Wilcoxon signed rank test and McNemar test. Inter- and intraobserver variability was determined with intraclass correlation coefficients (ICC) and Bland-Altman plots.

Results

For lung and mediastinal windows, nodule size was significantly larger using long-axis diameter rather than average diameter (16.93 vs. 14.92 mm, P < .001; and 14.02 vs. 12.17 mm, P < .001, respectively). The correlation of CT with pathologic measurements was stronger with long-axis than with average diameter (ICC 0.808 vs. 0.730; and 0.731 vs. 0.621, respectively). Lung window measurements correlated stronger with pathology than mediastinal window measurements. CT T-stages differed from pathology T-stages in more than 20% of nodules ( P < .001). Inter- and intraobserver variability was small with long-axis and average diameter (ICC range 0.96–0.991, and 0.970–0.993, respectively), but long-axis diameter showed wider scatter on Bland-Altman plots.

Conclusions

Long-axis CT diameter is preferable for T-staging because it better reflects the pathology T-stage. Average CT diameter might be used for longitudinal nodule follow-up because it shows less measurement variability and is more conservative in size assessment.

Introduction

The size of solid lung nodules detected on computed tomography (CT) has a substantial impact on their management. Indeed, current management guidelines consider nodule size a key parameter for both incidentally detected nodules and those seen in the framework of CT lung cancer screening . The approaches to how nodule size is measured and expressed, however, differ. Whereas some authors recommend that the long-axis diameter of a nodule should be used , others suggest that the average of long-axis and short-axis diameters should be calculated . To date, no general consensus has been reached over which of these two approaches is more accurate.

This may, in part, be caused by the paucity of studies comparing CT measurements of solid nodules to measurements obtained by pathology, which is commonly considered the reference standard for determining nodule size . Such comparisons could help quantify potential differences between the two measurement approaches and gauge the consequences that these differences have for the management of solid nodules, notably with respect to tumor (T)-staging.

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Materials and Methods

Study Material

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CT Acquisition

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Nodule Measurements

CT

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Pathology

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TABLE 1

The Number of Nodules Allocated to Stages T1a, T1b, and T2a, by Pathology and CT Measurements

Pathology CT Average Diameter Long-axis Diameter Lung Window Mediastinal Window Lung Window Mediastinal Window T1a † 194(70.80%) 222(81.02%) 238(86.86%) 193(70.44%) 223(81.39%) T1b † 59(21.53%) 52(18.98%) 36(13.14%) 72(26.28%) 45(16.42%) T2a † 21(7.66%) 0 \* 0 \* 9(3.28%) 6(2.19%)

AJCC, American Joint Committee on Cancer; CT, computed tomography.

The overall number of nodules was 274.

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Statistical Analysis

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Comparison of CT diameters and pathology diameters

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Comparison of long-axis diameter and average CT diameter

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Variability of CT measurements

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Results

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TABLE 2

Mean Diameters ± Standard Deviation (95%CI) of All 274 Nodules Measured by Pathology and the Two Observers on CT

Pathology Diameter (mm) CT Diameter (mm) Average Diameter Long-axis Diameter Lung Window Mediastinal Window Lung Window Mediastinal Window 17.76 ± 8.28

(16.78; 18.75) Observer 1 14.89 ± 5.78 12.06 ± 6.44 16.90 ± 6.69 13.94 ± 7.35 (14.20; 15.58) (11.29; 12.82) (16.11; 17.69) (13.07; 14.81) Observer 2 14.96 ± 6.28 12.29 ± 6.76 16.95 ± 7.23 14.09 ± 7.76 (14.21; 15.70) (11.49; 13.09) (16.09; 17.81) (13.17; 15.01)

CI, confidence interval; CT, computed tomography.

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Comparison of CT Diameters and Pathology Diameters

Long-axis CT Diameter

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Average CT Diameter

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Comparison of Long-axis Diameter and Average CT Diameter

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Variability of CT Measurements

Interobserver Variability

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Intraobserver Variability

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Discussion

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Acknowledgment

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References

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Size Measurement and T-staging of Lung Adenocarcinomas Manifesting as Solid Nodules ≤30 mm on CT

Rationale and Objectives

Materials and Methods

Results

Conclusions

Introduction

Materials and Methods

Study Material

CT Acquisition

Nodule Measurements

CT

Pathology

Statistical Analysis

Comparison of CT diameters and pathology diameters

Comparison of long-axis diameter and average CT diameter

Variability of CT measurements

Results

Comparison of CT Diameters and Pathology Diameters

Long-axis CT Diameter

Average CT Diameter

Comparison of Long-axis Diameter and Average CT Diameter

Variability of CT Measurements

Interobserver Variability

Intraobserver Variability

Discussion

Acknowledgment

References

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