Small patchy shadow in the left lower lung suggests limited infectious inflammation in the left lower lung. The cause of the infection needs to be further considered whether it is a common bacterial, viral infection, tuberculosis infection, or a tumor complication caused by tumor cells. Therefore, if chest imaging chest radiograph or CT reveals a small patchy shadow in the left lower lung, further systemic investigations, including routine blood tests, are needed to find out whether the infection is bacterial or not. Sputum test for Mycobacterium tuberculosis as well as tuberculosis antibody test should be done to further clarify whether the infection is tuberculosis. Do sputum test for tumor cells and chest enhancement CT, fiberoptic bronchoscopy to clarify whether the tumor is caused by obstructive pneumonia and other changes. Therefore, the small shadow in the left lower lung needs to be closely observed, and sometimes it can be given anti-infection for two weeks, and then review chest imaging, if the small shadow disappears in the review chest imaging, it is most likely to suggest that it is a common bacterial infection. If the small shadow in the left lower lung does not disappear, it is necessary to further investigate whether it is tuberculosis or neoplastic lesion.