When there is gas accumulation in the subcutaneous tissue of the chest, it is called subcutaneous emphysema. When the skin of subcutaneous emphysema is pressed by hand, it can cause the gas to move in the subcutaneous tissue, and the feeling of twisting hair or gripping snow can appear. When pressing the subcutaneous emphysema with a stethoscope, a sound similar to the twisting of hair can be heard. Subcutaneous emphysema in the chest is usually caused by gas escaping from the lesion and accumulating under the skin after damage to the lung, trachea or pleura. Occasionally it occurs as a result of localized gas-producing bacillus infection. In severe cases, gas may spread subcutaneously from the chest wall to the neck, abdomen, or other areas of the skin. Etiology This pathology is caused by rupture of the cervical or subclavian air sac due to improper management or rough catching, or by gas spilling subcutaneously due to puncture of the air sac by other sharp objects, resulting in subcutaneous emphysema. In addition, the gas can also escape into the subcutis due to the fracture of bones with gas cavity such as humerus, urochondrium and sternum. 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, it is seen secondary to endoscopic injury. There are usually three ways for air to enter the subcutaneous tissue through the damaged area: 1.When the pneumothorax is accompanied by wall pleura 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 tissues of the chest; 3, air enters subcutaneous tissues directly through the body surface wound of the chest wall.