A thin-walled air-containing cavity in the anterior segment of the upper lobe of the left lung is often considered to be caused by pulmonary alveoli, pulmonary cysts, emphysema and other diseases. 1. Pulmonary alveolus: due to the lesion of small bronchial tubes in the lungs, the pressure of alveolus rises, rupture and fusion will form an air-containing cavity, which can be detected by chest CT or chest X-ray. 2. Lung cysts: manifested as cystic lesions of different sizes of gas or air-fluid in the lungs, and air-containing cavities may appear, which are mostly related to lung infections and congenital embryonic dysplasia. 3. Emphysema: due to the loss of elasticity of alveoli and alveolar sacs, causing over-inflation and expansion of alveoli, which may lead to the emergence of air-containing cavities. A thin-walled air-containing cavity in the anterior segment of the upper lobe of the left lung can also be seen in other diseases, and it is recommended that the patient go to the hospital in time for examination to find out the cause of the disease, and actively cooperate with the doctor to receive treatment.