Subcutaneous emphysema of the chest wall is usually secondary to sternal and/or rib fractures with pneumothorax, especially in patients with multiple multiple rib fractures with tension pneumothorax, and can also be complicated by tracheal, bronchial, pulmonary, and esophageal injuries. Occasionally, they are seen secondary to endoscopic injuries. There are usually three ways for air to enter the subcutaneous tissue through the damaged area: 1, when the pneumothorax is accompanied by wall pleural damage, the air in the chest cavity can enter the subcutaneous tissue of the chest wall through the damaged area; 2, when the trachea, bronchus or esophagus is ruptured, the air can enter the mediastinum directly through the rupture, and then diffuse to the neck, face and subcutaneous tissue of the chest through the superior sternal recess; 3, when the air enters the chest wall directly through the rupture. 3. air enters the subcutaneous tissue directly through the body surface wound of the chest wall. This pathology is due to improper management, rough catching, rupture of the cervical air sac or subclavian air sac, or gas spillage under the skin due to other sharp objects piercing the air sac, forming subcutaneous emphysema. In addition, gas can also escape into the subcutis when fractures occur in bones with air cavities, such as the humerus, ossicles and sternum. Patients with subcutaneous emphysema generally have no conscious symptoms, and the only effect on the patient is difficulty in opening the eyes. Patients with mediastinal emphysema often complain of chest tightness or pain behind the sternum, and may also have hoarseness of voice. The subcutaneous tissue is swollen and has a spongy sensation to touch and a sensation of twisting and stepping on snow. If a rough crunching sound is heard along with the heartbeat, this is seen in mediastinal emphysema. Severe mediastinal emphysema may affect venous return, resulting in jugular venous dilatation, tachycardia, respiratory distress, and even heart failure. The skin of chest wall is swollen after chest injury, and if sponge sensation and twisting pronunciation are palpated by light finger pressure, it indicates subcutaneous emphysema, which is generally not easily missed or misdiagnosed. Careful clinical observation is helpful to clarify the source of emphysema. If the emphysema first manifests in the neck, its source should be considered as a possible mediastinal emphysema. X-ray examination can help to further identify the source of the emphysema.