Radiological prediction of tumor invasiveness of lung adenocarcinoma on thin-section CT

Abstract

To evaluate thin-section computed tomography (CT) (TSCT) features that differentiate adenocarcinoma in situ (AIS), minimally invasive adenocarcinoma (MIA), and invasive adenocarcinoma (IVA), and to determine the size of solid portion on CT that correlates to pathological invasive components. Forty-eight patients were included. Nodules were classified into ground-glass nodule (GGN), part-solid, solid, and heterogeneous. Visual density of GGNs was subjectively evaluated using reference standard images: faint GGN (Ga), <-700 Hounsfield unit (HU); intermediate GGN (Gb), from -700 to -400 HU; dense GGN (Gc), >-400 HU; and mixed (Ga + Gb, Ga + Gc, and Gb + Gc). The evaluated TSCT findings included margin of nodule, distribution of solid portion, distribution of air bronchiologram, and pleural indentation. The longest diameters of the solid portion and the entire tumor were measured. Invasive diameters were measured in pathological specimens. Twenty-two AISs (16 GGNs [7 Ga, 5 Gb, 2 Gc, 1 Ga + Gc, 1 Gb + Gc], 4 part-solids, and 2 heterogeneous), 6 MIAs (1 GGN [Gb + Gc], 3 part-solids, and 2 solids), and 20 IVAs (1 GGN [Gb], 3 part-solids, and 16 solid) were found. The longest diameter (mean ± standard deviation) of the solid portion and total tumor were 9.7 ± 9.7 and 18.9 ± 5.6 mm, respectively. Significant differences in TSCT findings between AIS and IVA were margin of nodule (Pearson chi-squared test, P = 0.004), distribution of air bronchiologram (P = 0.0148), and pleural indentation (P = 0.0067). A solid portion >5.3 mm on TSCT indicated MIA or IVA, and >7.3 mm indicated IVA (receiver operating characteristic analysis, P < 0.0001). Irregular margin, air bronchiologram with disruption and/or irregular dilatation, and pleural indentation may distinguish IVA from AIS. A 5.3 to 7.3 mm solid portion on TSCT indicates MIA/IVA, and a solid portion >7.3 mm on TSCT indicates IVA.

Figure 1

Tumor diameter (red arrow) was 15 mm, and collapse diameter (green arrow) was 1.5 mm. As seen in this case, if multiple microinvasive areas (blue arrow-1, 3 mm; and blue arrow-2, 1.5 mm) are found in 1 tumor, the largest invasive diameter (blue arrow-1) was selected and the size was recorded. The diameter of invasive component in this case was 3 mm.

Figure 2

Visual classification of nodules. (A) Ground-glass nodule (GGN), (B) part-solid nodule, (C) solid nodule, (D) heterogeneous nodule: this type of nodule indicates GGN with complicated distribution of solid-like portions.

Figure 3

Classification of ground-glass nodule (GGN) by 3 ranges of Hounsfield unit (HU). Faint GGN (Ga): CT value is <−700 HU. Intermediate GGN (Gb): CT value is from −700 HU to −400 HU. Dense GGN (Gc): CT value is >400 HU.

Figure 4

Each thin-section CT finding in 2 cases of adenocarcinoma in situ (AIS) and in 1 case of invasive adenocarcinoma (IVA). This nodule was histopathologically confirmed as AIS. CT image showed ground-glass nodule, which consisted of 2 kinds of ground-glass densities (Ga + Gc). (B) This nodule was histopathologically confirmed as AIS. CT image showed part-solid nodule, in which solid portion included air bronchiologram without any disruptions and irregular dilatations. Solid portion correlated to the pathological collapse area. (C) This nodule was histopathologically confirmed as IVA with acinar, papillary, and micropapillary cells. CT image showed irregular solid nodule including air bronchiologram with disruptions and irregular dilatations. Pleural indentation can be seen.

Figure 5

Receiver operating characteristic analysis for 2 groups: nodules with pathological invasiveness ≤5 mm (n = 33) and >5 mm (n = 15). Cutoff value of solid portion on thin-section CT was more than 7.3 mm to predict the pathological invasiveness >5 mm (P < 0.0001): sensitivity, 93.3%; specificity, 66.7%.

Figure 6

Receiver operating characteristic analysis for 2 groups: nodules with adenocarcinoma in situ (n = 22) and nodules with minimally invasive adenocarcinoma (MIA) or invasive adenocarcinoma (IVA) (n = 26). Cutoff value of solid portion on thin-section CT was more than 5.3 mm to predict the histological diagnosis (MIA or IVA) based on the pathological invasiveness (P < 0.0001): sensitivity, 92.3%; specificity, 90.9%.