Thickening of the interlobular septum of the lungs may be the result of chest CT, chest X-ray, and may be caused by lung infection, cardiac insufficiency, malignant lung diseases, etc. 1. Lung infection: Inflammation of the lungs due to infection by bacteria, Mycobacterium tuberculosis, parasites, etc., which may cause congestion and edema of the interlobular septa and thickening of the interlobular septa when it is more obvious. 2. Cardiac insufficiency: pulmonary edema, connective tissue disease, secondary interstitial lung disease and other diseases caused by cardiac insufficiency may lead to thickening of the interlobular septum. 3. Malignant lung diseases: such as bronchopulmonary cancer, alveolar cell carcinoma, foci caused by metastasis of cancers from other organs to the lungs, causing thickening of interlobular septa in both lungs. Therefore, if the chest CT result shows thickening of interlobular septum of lungs, one should go to the hospital as soon as possible to clarify the cause of the disease, and actively cooperate with the doctor to carry out standardized treatment after the diagnosis is confirmed.