In the process of PIL developing to MIA and IAC, with the increase of tumor cell infiltration and tumor size, the growth rate and resistance of tumor cells in all directions were uneven, the degree of cell differentiation is diverse, and the morphological signs are gradually relatively obvious. According to a study by Oda et al. [15], the occurrence rate of spicule sign in IAC was higher than that in PIL, the difference was statistically significant. Wang et al. [16] reported that the incidence of pleural traction sign, lobulation sign, bronchial cut-off sign, air bronchogram sign and spicule sign in IAC was significantly higher than that in MIA and PIL, while there was no significant difference in cavity sign among the three groups. In our research there was no significant difference in the distribution of vacuole sign in PIL, MIA and IAC, but the incidence of cavity sign in IAC was higher than that in the other two groups, and the difference was statistically significant(P<0.01). The subjects of Wang’s paper were all small adenocarcinomas with a certain proportion of ground-glass density lesions, but our study included solid lesions, which may be the reason why the results were inconsistent.
The formation of lobulation sign is mainly related to the different growth rates of lesions in different directions. According to the study of Lee et al. [17], the size, density, lobulation sign, spicule sign and pleural traction sign of the lesion are of great significance in the differential diagnosis between IAC and non-IAC. The findings of our study suggest that the incidence of lobulation sign in IAC group was significantly higher than that in PIL and MIA, which were consistent with the above view. Xiang et al. [18] reported that the signs of air bronchogram and tumor vascular are meaningful for predicting the infiltration degree of lung adenocarcinoma. The occurrence of air bronchogram sign in PIL, MIA and IAC were 14.1%, 15.9% and 43.7% respectively in our paper, and the incidence rate of tumor vascular sign in the three groups was 4.2%, 6.8% and 38.4% respectively. The results showed that the incidence of the two signs in IAC was meaningfully higher than that in the other two groups, and the difference was statistically momentous (P < 0.05). The conclusions of the two studies were consistent. According to many articles in the field, the incidence of these two signs in IAC is higher than that in non-IAC, which is consistent with the consequences of our investigation. It shows that air bronchogram sign and tumor vascular sign have important significance in the differential diagnosis between IAC and non-IAC [19].
The size of the lesion was divided into three grades in our paper, the results display the size of PIL was no significant difference from MIA (P > 0.05), the size of IAC lesions was significantly larger than that of PIL and MIA (P < 0.05). Recent research has reported that the average axial diameter of IAC is larger than that of non-IAC lesions [20]. The above outcome are consistent with the results of our study, which indicated that pure ground-glass density lesions accounted for 80.3%, 70.5% and 3.9% of PIL, MIA and IAC, no solid lesions were found in 71 cases of PIL, solid lesions accounted for 2.3% and 68.1% of MIA and IAC (P<0.05). In the results of Heidinger et al. [21], PIL can be shown pure-ground glass density lesions, and the incidence of pure ground-glass density lesions in MIA was about 40%, while the incidence in IAC was significantly less, which was consistent with the results of our study. Then the study by Eguchi et al. [22] also considered that the degree of infiltration for lung adenocarcinoma was positively correlated with the size and density of the lesion, which was consistent with the results of our study. In pure ground-glass lesions, the distribution of air bronchogram sign, spicule sign, and vascular cluster sign in PIL and MIA was different [23]. However, there was no difference in the signs between the two groups in this study. The reason for the different results may be that the lesions collected in this paper included pure ground-glass, mixed ground-glass and solid cases.
The results of previous studies [24-26] could show that the size, density, lobulation, spicule and pleural traction signs of lung adenocarcinoma were different in the incidence of highly and poorly differentiated adenocarcinoma, but there was no statistical difference in the incidence of air bronchogram and tumor vascular signs. In our study, pleural traction sign, spicule sign, tumor vascular sign, bronchial cut-off sign and cavity sign in poorly differentiated subgroup were significantly higher than in the other two subgroups, then there was no difference in vacuole sign among the three subgroups (P > 0.05). In this study, the incidence of air bronchogram sign in the highly differentiated subgroup were higher than the moderately subgroup while the lobulation sign was the lowest among subgroups (P < 0.05), which was consistent with the Ref. [27]. And those differences could be related to the different grouping methods of these studies.
In our study the incidence of lesions of ≤1.5cm, 1.5~3cm and >3cm in the highly differentiated subgroup was about 7.4%, 75.8% and 16.8% respectively, and the lesions of 1.5~3cm were significantly higher than the other two subgroups (P<0.05). Only one case in moderate differentiation subgroup was less than 1.5 cm in 66 cases, while in the poorly differentiated subgroup, the lesion was more than 3 cm, accounting for 69.5%, which was significantly higher than that in the other two subgroups (P < 0.05). The incidence of pure ground-glass lesions in the highly differentiated subgroup was significantly higher than that of the other two subgroups, the most common lesions in the poorly differentiated subgroup were solid lesions (P < 0.05). The incidence of mixed ground-glass density lesions in the high and moderate differentiation subgroups were higher than that in the poorly differentiated subgroup (P <0.05). The study indicated that with the increase of differentiation degree of invasive adenocarcinoma, the density and size of the lesions gradually increased, which were consistent with the Ref. [28-29].