Left lung hyperdense shadow refers to lesions or foci in the left lung that are denser than normal lung tissue on imaging, which are commonly seen in lung infections, lung tumors, old foci and other diseases. 1. Lung infection: high density shadow in the left lung is most common in pneumonia, including viral pneumonia, bacterial pneumonia, mycoplasma pneumonia and so on. Tuberculosis, fungal infection of the lung, lung abscess, bronchiectasis and other imaging examinations of the lung can also appear dense shadow. 2. Lung tumors: including malignant tumors (e.g. primary lung cancer, metastatic lung cancer, etc.) and benign tumors (e.g. misshapen tumors, pulmonary sarcoidosis, etc.), which can be manifested as mass or rounded high-density solid shadows. 3. Old foci: commonly found in fibrous foci and calcified foci left after tuberculosis or lung infection. 4. Other diseases: such as pulmonary edema caused by various reasons, traumatic pulmonary hematoma, idiopathic pulmonary fibrosis and so on. High density shadow in the left lung, suggest that the patient go to the hospital in time to avoid delaying the condition.