Predictors of CT Morphologic Features to Identify Spread Through Air Spaces Preoperatively in Small-Sized Lung Adenocarcinoma

Abstract

Objectives: This study aimed to explore the predictive CT features of spread through air spaces (STAS) in patients with small-sized lung adenocarcinoma.

Methods: From January 2017 to May 2019, patients with confirmed pathology of small-sized lung adenocarcinoma (less than or equal to 2 cm) and who underwent surgery were retrospectively analyzed. The clinical, pathological, and surgical information and CT features were analyzed.

Results: A total of 47 patients with STAS (males, 61.7%; mean age, 56 ± 8years) and 143 patients without STAS (males, 58%; mean age, 53 ± 11 years) were included. Pathologically, papillary, micropapillary, solid predominant subtypes, and vascular and pleural invasion were most commonly observed features in the STAS group. Radiologically, higher consolidation tumor ratio (CTR), presence of spiculation, satellites, ground glass ribbon sign, pleural attachment, and unclear tumor-lung interface were more commonly observed features in the STAS group. CTR, presence of ground glass ribbons and pleural connection, and absence of cystic airspaces were considered as stable predictors of STAS in multivariate logistic models. The receiver operating characteristic curve (ROC) analysis for predicting STAS demonstrated higher area under the curve (AUC) in the model that used CTR (0.760, 95% confidence interval, 0.69-0.83) for predicting STAS than in the model that used long diameter of entire lesion (0.640).

Conclusions: CTR is the best CT sign for predicting STAS in small-sized lung adenocarcinoma. The ground glass ribbon is a newly found indicator and has the potential for predicting STAS.

Keywords: adenocarcinoma of lung; bronchial neoplasms; spread through air spaces; tomography; x-ray computed.

Figure 1

Flowchart of patient selection procedure. STAS, spread through air spaces; CT, computed tomography.

Figure 2

(A) Axial CT image of pGGO performed STAS pathologically. A ground glass ribbon sign was observed on the margin of the lesion and extended to the adjacent costal parietal pleura (white arrow), which was defined as a CT finding of a band-shaped ground glass opacity with blurred edge that emits from the edge of the nodule and extends into the adjacent lung (B). Multi-plane reconstruction with ground glass ribbon sign as the long axis. The shape of ribbon sign was displayed more clearly after adjusting the window width and level.

Figure 3

Bar graph shows the comparison of predominant subtypes between STAS-positive and STAS-negative groups (A); there is statistically significant difference in CTR between the two groups (B); the number of SNs in STAS group is more than that in non-STAS group (C); presence of spiculation, satellites, and ground glass ribbon sign, pleural attachment, and unclear tumor–lung interface was more common in STAS group (D). *P<0.05; **P<0.01; ***P<0.001; ****P<0.0001.

Figure 4

(A, D) Baseline axial (A) and coronal (D) CT images of STAS-positive adenocarcinoma in a 51-year-old man. An irregular ground glass nodule with multiple cystic cavities was detected with clear edges, so he was recommended 6–12 months follow-up (B, C, E). Axial CT images on the 8-month follow-up (B, C). The entire size of the lesion did not change, but some cysts were larger than before, and a ground glass ribbon sign was newly found on the edge of the lesion (black arrow), which was defined as a CT finding of a band-shaped ground glass opacity with blurred edge that emits from the edge of the nodule and extends into the adjacent lung (E). Coronal reconstructed image clearly shows the ribbon sign, stretching to the adjacent visceral pleural (black arrow) (F). The patient was recommended lung lobe resection and was confirmed invasive adenocarcinoma with STAS pathologically. Photomicrograph shows single cell pattern STAS consisting of scattered discohesive single cells (green arrow).

Figure 5

The ROC analysis for predicting STAS demonstrated higher area under the curve (AUC) in the model that used CTR (0.760, 95% confidence interval, 0.69–0.83) for predicting STAS than in the model that used long diameter of entire lesion (0.640).

Figure 6

STAS in a 45-year-old man with micropapillary predominant subtype of invasive adenocarcinoma (A). Multiplanar reconstructed CT image (width, 1,500 HU; level, −600 HU) shows a ground glass-density spiculation extending into the adjacent lungs (arrow), and several ground glass-density satellite foci with a diameter of 1–2 mm were observed at the edge of the lesion (white triangle) (B). Photomicrograph shows multiple solid nests clusters alveolar disseminations at the edge of one side of the lesion (arrow), spreading through the interlobular fissure (black triangle) to the alveolar cavities of the adjacent pulmonary lobe (C). Volume render reconstructed image shows visceral pleural indentation (D). Photomicrograph shows visceral pleural invasion, indentation, and thickening.