Metastatic lesions from malignant growths elsewhere are frequently observed in the lungs, and such lesions may be very extensive without producing signs or symptoms of pulmonary disease.
If such metastatic lesions involve the pleura, effusion may produce distressing symptoms, but so long as the nodules remain in the parenchyma of the lungs they rarely occasion any discomfort. In contrast to this, a small malignant nodule arising in the lumen of the bronchus may produce marked evidence of pulmonary disease because of the occurrence of bronchial occlusion.
The presence or absence of bronchial obstruction is the most reliable criterion for differentiating primary and secondary malignant disease in the lungs, and yet it has been pointed out that growths that are secondary in the lungs may ulcerate through the wall of the bronchus and cause partial bronchial obstruction, with the production of the signs and symptoms that are seen in growths that