Rationale and Objectives
To investigate the volume-doubling time (VDT) of histologically proved pulmonary nodules showing ground glass opacity (GGO) at multidetector CT (MDCT) using computer-aided three-dimensional volumetry.
Materials and Methods
We retrospectively evaluated 47 GGO nodules (mixed n = 28, pure n = 19) that had been examined by thin-section helical CT more than once. They were histologically confirmed as atypical adenomatous hyperplasia (AAH, n = 13), bronchioloalveolar carcinoma (BAC, n = 22), and adenocarcinoma (AC, n = 12). Using computer-aided three-dimensional volumetry software, two radiologists independently performed volumetry of GGO nodules and calculated the VDT using data acquired from the initial and final CT study. We compared VDT among the three pathologies and also compared the VDT of mixed and pure GGO nodules.
Results
The mean VDT of all GGO nodules was 486.4 ± 368.6 days (range 89.0–1583.0 days). The mean VDT for AAH, BAC, and AC was 859.2 ± 428.9, 421.2 ± 228.4, and 202.1 ± 84.3 days, respectively; there were statistically significant differences for all comparative combinations of AAH, BAC, and AC (Steel-Dwass test, P < .01). The mean VDT for pure and mixed GGO nodules was 628.5 ± 404.2 and 276.9 ± 155.9 days, respectively; it was significantly shorter for mixed than pure GGO nodules (Mann-Whitney U-test, P < .01).
Conclusion
The evaluation of VDT using computer-aided volumetry may be helpful in assessing the histological entities of GGO nodules.
The introduction of computed tomography (CT) lung cancer screening has increased the number of detected ground glass opacity (GGO) nodules. Henschke et al reported that 44 (19%) of 233 positive results were lesions with GGO nodules; 15 (34%) of the 44 lesions were malignant. Among lesions with a solid component (mixed GGO nodules), 63% were malignant, nodules without solid components (pure GGO nodules) had a lower malignancy rate (18%). GGO nodules may be attributable to focal inflammation, focal interstitial fibrosis , atypical adenomatous hyperplasia (AAH) , bronchioloalveolar carcinoma (BAC) , or adenocarcinoma (AC) . Although the differentiation of BAC and AC, which are malignant, from other diseases is important, it can be difficult on a single CT study . Many inflammatory lesions resolve spontaneously or with antibiotic treatment , on the other hand, the size of GGO nodules attributable to BAC or AC gradually increases . As focal interstitial fibrosis and AAH with pure GGO tend to remain stable in size for months or years , monitoring the nodule size for several months by high-resolution CT (HRCT) can help in obtaining a differential diagnosis. The reported average doubling time of BAC, calculated from the maximal tumor diameter with the Schwartz equation , is very long (457–813 days on average) , therefore, visual evaluation of the growth rate on axial CT image may be unreliable.
Accurate three-dimensional (3D) computer-aided volumetry (CAV) software to assess pulmonary nodules with volumetric data obtained at multidetector CT (MDCT) is available . However, most of the software used in earlier studies only evaluated solid pulmonary nodules and CAV of GGO nodules can be difficult . We developed enhanced CAV software to measure not only the volume of solid and of GGO nodules; it yielded sufficiently accurate and reproducible volume measurements .
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Materials and methods
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Patients and Nodule Selection
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Table 1
Clinical and Pathologic Characteristics of All 47 GGO Nodules
AAH BAC AC Nodules (patients) 13 (9) 22 (20) 12 (10) Patient sex Male 6 6 3 Female 7 16 9 Mean age (year) 58.8 ± 13.1 63.9 ± 9.0 67.4 ± 6.1 GGO subtype Pure-GGO 13 14 1 Mixed-GGO 0 8 11 Mean maximum diameter (mm) 10.1 ± 3.2 13.3 ± 5.6 13.4 ± 4.6 Mean CT attenuation (HU) −614.5 ± 98.4 −611.4 ± 123.0 −323.3 ± 210.7 Mean interval between two CT scans (days) 331.6 ± 436.9 123.9 ± 118.5 85.9 ± 39.8
AAH, atypical adenomatous hyperplasia; BAC, bronchioloalveolar carcinoma; AC, adenocarcinoma.
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Image Acquisition
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Computerized Volumetry of Pulmonary Nodules
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Evaluation of Volume Doubling Time
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VDT=[log2×t]/[log(V2/V1)], VDT
=
[
log
2
×
t
]
/
[
log
(
V
2
/
V
1
)
]
,
where V 1 and V 2 are the initial and final nodule volume and t is the interval between the two CT scans. The software calculates the VDT automatically by comparing the nodule volume on the two scans ( Fig 2 ). The average value of the two radiologists’ measurements of VDT was adopted.
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Statistical Analysis
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Results
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Discussion
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