Small cavities in the lungs may be due to infection by pathogenic bacteria such as tuberculosis, bacteria, fungi, etc. They are also seen in malignant tumors of the lungs. 1. Tuberculosis: Mycobacterium tuberculosis can cause cavitary lesions in the lungs, mostly in the posterior segment of the upper lobe and the dorsal segment of the lower lobe of both lungs. In addition to respiratory symptoms such as cough and sputum, symptoms of tuberculosis toxicity such as fever, malaise and night sweats may occur, and sputum is positive for antacid bacilli. 2. Bacteria: such as staphylococcus aureus, anaerobic bacteria and a few mycobacteria, usually with high fever, chills, combined with anaerobic infections, sputum pus-flavored, severe symptoms, fast onset, rapid changes in the lesions, and anti-infective treatment can be significantly improved. 3. Fungus: mostly seen in long-term use of hormones, malignant tumors and other immunocompromised people. Symptoms are mild, there may be crescent sign, halo sign and other typical lung CT manifestations. 4. Lung malignant tumor: long-term smokers suffer from non-small cell lung cancer such as squamous cell carcinoma, lung adenocarcinoma, etc., which is easy to form cancerous cavities and may be accompanied by elevated specific tumor markers, coughing, coughing up sputum, hemoptysis, emaciation, dyspnea and other symptoms. There are more reasons leading to small cavity shadow in the lung, and it is suggested that patients should consult the doctor for examination and relevant treatment as soon as possible.