What is a pulmonary nodule? Lung nodules are spherical shadows in the lungs less than 3cm in diameter detected by chest X-ray or chest CT. Lung cancer often has no symptoms in its early stage, and its “traces” can only be detected by chest CT – lung nodules. Secondly, benign lung tumors with low incidence also tend to present as lung nodules. There are also a few infectious diseases of the lung (such as tuberculosis, fungus, mechanized pneumonia, etc.) and chronic proliferative lesions (such as adenomatous hyperplasia) that can form pulmonary nodules.