A shadow on the lungs means that a chest X-ray or CT of the lungs shows a mass, nodule, etc. It may mean congenital developmental abnormality of the lungs, lung infection, lung tumor and so on. 1. Congenital developmental abnormalities of the lungs. If the shadows presented in the images are round, thin-walled or slightly lobed masses, the patient may suffer from congenital developmental anomalies such as lung cysts and lung malformation tumors; 2. Bacterial, fungal or viral infection of the lungs. If the shadow is flaky or flocculent, then the patient may suffer from pneumonia, tuberculosis, pulmonary aspergillosis and other diseases; 3. Lung tumor. If it is lung cancer, the shadow is mostly spherical with lobulated edges. Pneumonic pseudotumor, on the other hand, is a spherical shadow with relatively clear edges. Shadows in the lungs may also be other types of diseases, and patients are advised to go to the hospital for a comprehensive examination in time to determine the specific disease, so as not to miss the best opportunity for treatment.