Pulmonary cysts can be seen in a variety of diseases, such as bronchopulmonary cysts caused by congenital lung dysplasia, cavities associated with tuberculosis infection, air sac infections associated with congenital pulmonary air sacs, cyst-like cavities arising from thickened walls of large pulmonary alveoli, bronchial infections with cystic changes in bronchial dilatation, and cancerous irregular cavities formed in cancer patients. If a cystic cavity appears on the lung, CT will indicate whether the size of the cavity is regular and whether the wall of the cavity is thickened. If the wall of cystic cavity is accompanied by liquid and gas plane, it means that the cystic cavity is accompanied by infection, and if the wall of cystic cavity appears irregular thickening, it should also be alert to whether it is the early manifestation of malignant tumor.