A 4mm ground glass nodule in the upper apical segment of the left lung is usually not serious. A 4mm ground glass nodule on the left lung is usually not serious if there are no uncomfortable symptoms. It is recommended that a repeat thin-layer chest CT be performed 6 to 12 months after discovery. If the solid component increases, surgery can be performed for treatment. If the size of the nodule is small, it means that the possibility of lung cancer is relatively low, and usually does not require special treatment, but still needs regular follow-up according to medical advice. It is important to note that although this is not a serious condition, it still needs to be taken seriously. This is mainly because most lung ground-glass nodules are malignant, so they should be examined in the thoracic surgery department without letting down your guard. There are many reasons for the presence of ground glass nodules in the upper apical segment of the left lung, such as lung infection and early lung adenocarcinoma. Usually, good results can be achieved after timely treatment, so do not panic too much.