Extrapulmonary malignant tumor cells can reach the lungs through the bloodstream, lymphatics, or direct extension, forming pulmonary metastasis.
Clinical presentation and pathology
Extrapulmonary malignant tumor cells return to the right heart through the systemic veins, and migrate to the lungs through the pulmonary artery. Metastasis in the hilar and mediastinal lymph nodes is disseminated to the intrapulmonary lymphatics; or malignant tumor in the mediastinum and chest wall can directly extend and invade the lungs. The clinical manifestations of pulmonary metastasis include cough, expectoration, thoracodynia, and hemoptysis. Most patients have symptoms of primary tumor, often accompanied by cachexia.
Imaging manifestations
X-ray
Hematogenous disseminated pulmonary metastases are manifested by multiple, homogeneous, variously sized, sharply marginated nodules or cannonball patterns in both lungs, mostly in the middle and lower fields of both lungs, but also unilateral lung fields; solitary spherical lesion may be present. Primary tumor with abundant blood supply may develop miliary metastases, mostly in the middle and lower lung fields; occasionally, they may show multiple, small, patchy, infiltrative opacities. Lymphatic metastasis may be manifested by enlargement of the hilar and/or mediastinal lymph nodes, and irregular linear opacities and beaded nodules radiating outward from the hilum.
Figure 1 Multiple pulmonary metastases
a. Frontal chest radiograph shows multiple, variously sized nodules in both lungs, mostly in the outer zone of the middle and lower lungs; b. CT lung window shows multiple, variously sized nodules in lower lungs, with smooth and clear edges.
CT
CT is more sensitive than chest x-ray to detect pulmonary metastatic lesions. Hematogenous lesions are manifested by diffuse, randomly distributed nodules or multiple spherical lesions in both lungs, with smooth edges and homogeneous density, mostly in the middle and lower lung fields and subpleural areas. Few metastatic tumors may have cavities, air cysts, or calcification. HRCT has unique advantages in the diagnosis of metastatic tumors through the lymphatic route; in addition to enlargement of the hilar and mediastinal lymph nodes, irregular thickening of the interlobular septa and beaded changes composed of multiple small nodules along the bronchial vascular bundles and interlobular septa can also be seen.
Diagnosis and differential diagnosis
On the basis of the history of primary tumor, multiple metastases in the lungs are easy to diagnose. If there is solitary metastasis in the lungs and the primary tumor is uncertain, the diagnosis is somewhat difficult; careful examination of each organ and blood tumor markers should be performed, and puncture biopsy of the lung mass can be performed to confirm the diagnosis if necessary.