Lung nodule 4a is a classification of imaging test, this classification indicates that this mass has some possibility of malignancy, it is recommended to further perform biopsy and other tests to clarify the benign or malignant nature. There are many causes of lung nodules, including malignant tumors such as lung adenocarcinoma, benign tumors such as lung malignancy, and benign inflammatory lesions such as tuberculous granuloma or pulmonary nodular disease. Depending on their respective imaging characteristics, these nodules are commonly categorized by the LUNG-RADS classification, with category 4a indicating that the nodule has a 5% to 15% chance of being malignant. For nodules with this classification, further PET-CT examination is recommended, after which pathological biopsy or surgical resection will be performed for lesions with a higher likelihood of malignancy according to the results of PET-CT examination. For lesions with a high likelihood of benignity on PET-CT, regular follow-up is recommended to observe the growth of the nodule, and timely surgical intervention is recommended in case of progressive enlargement. In conclusion, the presence of category 4a nodules is recommended to go to the hospital in time.