<unk>  <unk> , SE) occurs when gas or air accumulates and seeps under the skin, where normally no gas should be present.<unk>  refers to the<unk>  tissue, and<unk>  refers to trapped air pockets resembling the pneumatosis seen in pulmonary<unk> . Since the air generally comes from the chest cavity,<unk>  usually occurs around the upper torso, such as on the chest, neck, face, axillae and arms, where it is able to travel with little resistance along the loose connective tissue within the superficial fascia.<unk>  has a characteristic crackling-feel to the touch, a sensation that has been described as similar to touching warm Rice Krispies. This sensation of air under the skin is known as<unk>  crepitation, a form of Crepitus. Numerous etiologies of<unk>  have been described. Pneumomediastinum was first recognized as a medical entity by Laennec, who reported it as a consequence of trauma in 1819. Later, in 1939, at The Johns Hopkins Hospital, Dr. Louis Hamman described it in postpartum woman; indeed,<unk>  is sometimes known as Hamman's syndrome. However, in some medical circles, it can instead be more commonly known as Macklin's Syndrome after L. Macklin, in 1939, and M.T. and C.C. Macklin, in 1944, who cumulatively went on to describe the pathophysiology in more detail.<unk>  can result from puncture of parts of the respiratory or gastrointestinal systems. Particularly in the chest and neck, air may become trapped as a result of penetrating trauma (e.g., gunshot wounds or stab wounds) or blunt trauma. Infection (e.g., gas gangrene) can cause gas to be trapped in the<unk>  tissues.<unk>  can be caused by medical procedures and medical conditions that cause the pressure in the alveoli of the lung to be higher than that in the tissues outside of them. Its most common causes are pneumothorax or a chest tube that has become occluded by a blood clot or fibrinous material. It can also occur spontaneously due to rupture of the alveoli, with dramatic presentation. When the condition is caused by surgery it is called surgical<unk> . The term spontaneous<unk>  is used when the cause is not clear.<unk>  is not typically dangerous in and of itself, however it can be a symptom of very dangerous underlying conditions, such as pneumothorax. Although the underlying conditions require treatment,<unk>  usually does not; small amounts of air are reabsorbed by the body. However,<unk>  can be uncomfortable and may interfere with breathing, and is often treated by removing air from the tissues, for example by using large bore needles, skin incisions or<unk>  catheterization.
Subcutaneous emphysema
Bronchophony
Tracheal deviation
Tracheobronchomegaly
Barrel chest
Visakhapatnam gas leak
Pleural friction rub
Grand Rounds