Pulmonary cavities are formed when lung tissue is necrotic and liquefied and expelled through the bronchi and into the air. (1) Tuberculous cavities have the common features and common characteristics of secondary forms of pulmonary tuberculosis. Calcification and hypoperfusion are additional specific signs of tuberculous cavities. Calcification is mainly patchy, and laminar calcification is the most characteristic. Calcification of the adjacent bronchial wall and endothelium is correlated with the occurrence of tuberculosis and is formed by the collapse of calcified lymph nodes into the wall. In addition, the presence of multiple cavities with large differences in cavity morphology, relatively regular cavity walls, and the presence of mediastinal hilar lymph nodes is suggestive for the diagnosis of tuberculous cavities. (2) Among the imaging manifestations of cancerous cavities, wall nodules and large thick-walled cavities are relatively specific. However, since the tumor is extremely vascular, necrosis is usually not due to lack of blood vessels, but rather due to compression or destruction of blood vessels in the central part of the mass; the marginal contour and surrounding changes of cancerous cavities have common features of lung cancer: lobar sign, burr sign, spiny protrusion, vascular cluster sign, etc. Thickening of adjacent bronchial walls and luminal narrowing and obstruction are also more significant in suggesting malignant lesions. The cavities formed in acute lung abscesses are often single, large in size, and have irregular walls, while chronic lung abscesses have clear walls but irregular patterns and tend to form multiple cavities with smaller volumes. These two types of cavities have the characteristics of tension-type cavities. The cavity may also be surrounded by exudate and satellite foci, but the lung window and mediastinal window show significant changes in extent. In addition, enhanced examination shows an increase in the number of coarse but natural vascular shadows, which is known as the “beard sign”. The main imaging features of metastatic cavities are multiple, similar morphology, small size, and thick walls, and often coexist with multiple nodules. ⑤ Pulmonary cysts form cavity-like lesions with a thin wall of about 1 mm and the most regular shape. When repeatedly infected, the cyst wall can be thickened and deformed by fibrotic changes, and “air-fluid planes” can appear in the cavity, but the liquid contents are relatively low in density and homogeneous, and inflammatory infiltration can also appear around them, which should not be distinguished from lung abscess. (6) It is difficult to distinguish Wegener’s granulomatous cavity from some metastatic cavities in the lung, which generally have smooth and sharp edges, and the former have wandering characteristics on follow-up. Among the imaging manifestations of carcinoma cavities in lung cases, wall nodules and large thick-walled cavities are relatively specific. (7) Pulmonary fungal infections tend to form cavitary lesions, which are a type of inflammatory cavity in the lung, often manifesting as multiple high-density masses with residual irregular air-containing cavities, formed after the necrotic material in the center of the inflammatory granuloma drains from the bronchus. Some of the solitary masses are surrounded by the “air half-moon sign” and intraluminal motile Aspergillus balls. Fungal infections tend to form cavitary lesions, which are a type of inflammatory cavity in the lung.