Visceral pleural invasion by pulmonary adenocarcinoma ≤3 cm: the pathological correlation with pleural signs on...

(I) To categorize and quantitatively analyze pleural signs on CT of pulmonary adenocarcinoma (≤3 cm); (II) to evaluate the association between pleural signs and visceral pleural invasion (VPI) of adenocarcinoma.

The clinical data of 52 pulmonary adenocarcinoma patients with 91 involved pleurae were retrospectively analyzed in one single institution. Pleural signs were categorized into five types of non-interlobar fissure pleura (group A) and four types of interlobar fissure pleura (group B). A new parameter called pleural indentation fraction (PIF) was firstly defined to quantitatively evaluate the level of pleural shift.

In group A, type I pleural sign accounted for 15.79%, type II for 31.58%, type III for 21.05%, type IV for 10.53%, type V for 21.05%. The PIF of type II-III was 0.494±0.204. In group B, type I accounted for 67.65%, type II for 14.71%, type III for 8.82%, type IV for 8.82%. The PIF of type I was 0.188±0.083, significantly different with type II-III of group A (t=-7.444, P<0.001). The PIF of type I in group B had significant linear correlation with the tumor distance to the primary pleura. 41 patients with 75 involved pleurae formed the study part of pathological correlation with pleural signs. The rate of VPI was 87.5% (type III), 80% (type IV) in group A and 84.2% (type I), 40% (type II) in group B (t=30.895, P<0.001). The ratio of type III in group B was 2/2. Four cases with non-intact extrapleural fat layer were pathologically confirmed with VPI in type IV of group A. Six of seven cases with mediastinal pleural abnormality (type II-IV) were confirmed with VPI.

Pleural signs can be categorized into five types of group A and four types of group B in the study. Type III-IV of group A and type I and III of group B may be indicators to VPI. Non-intact extrapleural fat layer and mediastinal pleural abnormality may increase the diagnosis accuracy of VPI.