There are many causes of lung tissue necrosis, such as ischemic necrosis, infectious necrosis, tumor necrosis and so on. 1. Ischemic necrosis: ischemic necrosis of lung tissue is mostly seen in patients with severe pulmonary thromboembolism, when the pulmonary artery branch is severely embolized within the scope of its blood supply, ischemic necrosis can occur, called pulmonary infarction. 2. Infectious necrosis: Infectious necrosis is mostly secondary to bacterial or tuberculosis infection, bacteria or tuberculosis seriously damage normal lung tissue can lead to lung tissue necrosis, and then form lung abscess or caseous necrosis. 3. Tumor necrosis: lung cancer or metastatic lung tumor can invade normal lung tissue, secondary infection and then cause lung tissue necrosis, forming cavities or abscesses. In addition to the above reasons, pneumoconiosis, fungal infection of the lung and rejection reaction after lung transplantation can cause lung tissue necrosis.