Lung nodule class 4a suggests that the nodule is suspicious for malignancy and further PET-CT is recommended; if it is resorbed on follow-up, it suggests a benign lesion that is not serious; if it is enlarged, it is more serious and surgical resection is recommended. Lung nodules undergo CT examination, if the nodule is graded 4a using Lung-RADS, it indicates that the nodule has the possibility of malignancy, and its degree of malignancy is between 5% and 15%. Further PET-CT is recommended to evaluate the nature of the nodule. If PET-CT shows negative or mild uptake, CT follow-up is recommended in about half a year, and if there is any increase in size, pathologic biopsy or surgical resection is required. If the PET-CT test shows moderate or strong uptake, immediate pathologic biopsy or surgical resection is recommended. The presence of a pulmonary nodule category 4a is not always malignant, but caution is advised. The presence of pulmonary nodule category 4a requires active medical consultation and rational treatment as prescribed by the doctor.