Using CT features of cystic airspace to predict lung adenocarcinoma invasiveness

Background: Lung adenocarcinoma associated with cystic airspace (LACA) was once considered an uncommon manifestation of lung adenocarcinoma (LUAD), and understandings of it are limited; however, it is being observed more frequently in clinical practice. This study sought to assess the prevalence of LACA, and compare the high-resolution computed tomography (HRCT) features of LACA in patients with varying degrees of invasiveness.

Methods: This study retrospectively reviewed the HRCT scans of 1,525 patients with LUAD ≤3 cm in diameter at the Shanghai Chest Hospital between January 2016 and May 2016. Each nodule was examined to detect the presence of cystic airspace. Additionally, we analyzed the qualitative HRCT findings of the cystic airspaces, including the pattern, number, wall component density, distribution, inner surface, mural nodules, septa, and vessels passing through the cystic airspace using the Pearson χ² test or Fisher's exact test as appropriate. We also analyzed the quantitative measurements, such as the cystic airspace diameter, wall thickness, and thin-wall proportion, using a one-way analysis of variance or the Kruskal-Wallis rank-sum test as appropriate.

Results: LACAs were observed on HRCT in 11.5% (176/1,525) of the patients, of whom 7.1% (36/505) had pure ground-glass nodules, 13.5% (112/830) had mixed ground-glass nodules, and 14.7% (28/190) had solid nodules (P=0.001). The surgical procedures for LACAs varied (P=0.012). The incidence of LACAs increased as nodule diameter and invasiveness increased (both P<0.001). Statistically significant differences were observed in the wall component density, distribution, septa, vessels passing through the cystic airspace, cystic airspace diameter, wall thickness, and thin-wall proportion among the preinvasive lesion (PL), minimally invasive adenocarcinoma (MIA), and invasive adenocarcinoma (IAC) groups (P<0.001, P=0.024, P=0.001, P=0.025, P=0.001, P<0.001, and P<0.001, respectively). Wall component density increased as invasiveness increased (P<0.001). Unlike those in the MIAs and IACs, cystic airspaces in PLs typically lacked septa (P=0.001, and P<0.001, respectively). The IACs had larger cystic airspace diameters than the PLs (6.5 vs. 3.7 mm) (P<0.001). The IACs also had thicker wall thickness (11.8 vs. 6.8 mm, 11.8 vs. 8.3 mm) (P<0.001, and P<0.001, respectively) and smaller thin-wall proportions (181.5° vs. 264.8°, 181.5° vs. 223.8°) (P<0.001, and P=0.039, respectively) than the PLs and MIAs.

Conclusions: The prevalence and characteristics of cystic airspaces on HRCT can be used to predict invasiveness in patients with LUADs ≤3 cm in diameter.