To investigate the high resolution CT (HRCT) features of lung adenocarcinoma for differentiating synchronous multiple lung adenocarcinoma from lung adenocarcinoma with intrapulmonary metastasis.

The clinical and imaging features of 131 lesions from 62 patients of synchronous multiple primary lung adenocarcinoma (primary group) and 67 lesions from 31 patients of lung adenocarcinoma with intrapulmonary metastases (metastasis group) were retrospectively analyzed. According to the types of lesion, including pure ground glass nodule (pGGN), mixed ground glass nodule (mGGN) and solid nodule (SN), the image feature matching types of patients were divided into 7 types. The differences of image feature matching types between the primary group and the metastasis group were compared. Multiple lesions in the lung of patients were classified into the main lesion and the concomitant lesions according to their size. The differences including the size of the main lesion and the concomitant lesion (long diameter of nodule, long diameter of solid component in nodule), whether it contains ground glass components in nodule, shape, lobulation, margin, spiculation, bubble-like lucency, pleural retraction and pleural attachment were recorded and analyzed. The differences of image features of main lesion and the concomitant lesion in the primary group and the metastasis group were compared.

The image feature matching types of pGGN + mGGN and mGGN + mGGN were more common in the primary group, and the ground glass component contained pGGN or mGGN was accounted for 62.9%(39/62). At least one lesion containing the ground glass component was accounted for 96.8% (60/62). There were two types in metastatic groups, mGGN+ SN and SN+ SN accounting for 6.5% (2/31) and 93.5% (29/31), respectively. There were significant differences in image feature matching types between the primary group and metastatic group (P<0.01). Univariate analysis of the main lesions between the two groups showed that the gender, smoking history, long diameter of the main lesion, long diameter of the solid component, the ground glass component and pleural attachment were statistically different (P<0.05). Further analysis by multivariate logistic regression showed that the male (OR=5.742, P=0.010), SN (OR=41.291, P<0.01) and pleural attachment (OR=9.288, P=0.001) were the three significant risk factors associated with the main lesions in metastasis group.The most common concomitant lesions in primary group were pGGN, containing the ground glass component. However, all of the concomitant lesions in the metastatic group were SN (P<0.01), showing round lesions with well-defined margin, attaching the pleura (P<0.05).

The HRCT features of lung adenocarcinoma can differentiate synchronous multiple lung adenocarcinoma from lung adenocarcinoma with intrapulmonary metastasis. At least one lesion contains ground glass components (pGGN or mGGN) in synchronous multiple primary lung adenocarcinoma, while SN is more common in lung adenocarcinoma with lung metastasis. Lung cancer with intrapulmonary metastasis can be considered when the main lesion is SN with pleural attachment and the intrapulmonary accompanying lesion is also solid nodules without lobular, speculation and bubble-like lucency.

Lung neoplasms; Adenocarcinoma; Multiple primary; HRCT; Tomograph, X-ray computed; Differential diagnosis