Apical posterior segment occupancy in the upper lobe of the left lung belongs to the imaging terminology and refers to the presence of a mass shadow in the upper lobe of the left lung, which may be benign or malignant. Benign occupying lesions are most commonly seen as cysts, abscesses, and inflammatory granulomas as well as hemangiomas, cellular adenomas, nodular hyperplasia, and inflammatory pseudotumors. If the lesion is small and the patient has no obvious discomfort, no treatment is needed for the time being and regular review is sufficient; if the lesion is large, surgical treatment can be considered to alleviate it. Malignant space-occupying lesions are mostly seen in lung sarcoma, bronchopulmonary carcinoma, alveolar cell carcinoma, lung metastasis of extrapulmonary malignant tumors, etc. Targeted treatments, such as surgical treatments, radiotherapy or chemotherapy, can be carried out after clarification through examinations such as lung-enhanced CT, pathological tissue biopsy, and so on.