Ground glass nodules in the apical posterior segment of the upper lobe of the left lung may be caused by diseases such as pneumonia, tuberculosis or lung cancer. 1. Pneumonia: After the lungs are attacked by bacteria, it causes inflammatory disease leading to the existence of pneumonia. After the lungs are stimulated by inflammation for a long time, it is easy to cause ground glass nodules in the apical posterior segment of the upper lobe of the left lung. 2. Tuberculosis: Tuberculosis occurs in the posterior apical segment of the upper lobe and the dorsal segment of the lower lobe, which is an infectious disease of the lungs caused by Mycobacterium tuberculosis. The basic pathological features of patients with tuberculosis are exudation, caseous necrosis, and other proliferative tissue reactions, and it is manifested as ground-glass nodules in the imaging examination. 3. Lung cancer: some early lung adenocarcinoma can be manifested as ground-glass nodules in CT. If found that the border of ground-glass nodules in the lungs is not clear or there is trichiasis, it is necessary to improve the examination of lung cancer markers, and if necessary, puncture for pathology or excision and send to pathology, so as to avoid further deterioration of the tumor. Frosted glass nodules in the posterior apical segment of the upper lobe of the left lung may also be caused by other reasons, and it is recommended that patients go to the hospital in time to receive treatment after the cause of the disease has been clarified.