Subcutaneous emphysema pathophysiology

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Pathophysiology[edit | edit source]

Air is able to travel to the soft tissues of the neck from the mediastinum and the retroperitoneum (the space behind the abdominal cavity) because these areas are connected by fascial planes.^[1] From the punctured lungs or airways, the air travels up the perivascular sheaths and into the mediastinum, from which it can enter the subcutaneous tissues.^[2] Spontaneous subcutaneous emphysema is thought to result from increased pressures in the lung that cause alveoli to rupture.^[3]In spontaneous subcutaneous emphysema, air travels from the ruptured alveoli into the interstitium and along the blood vessels of the lung, into the mediastinum and from there into the tissues of the neck or head.^[3]

Trauma[edit | edit source]

Conditions that cause subcutaneous emphysema may result from both blunt and penetrating trauma;^[3] SCE is often the result of a stabbing or gunshot wound.^[4]

Chest trauma, a major cause of subcutaneous emphysema, can cause air to enter the skin of the chest wall from the neck or lung.^[5] When the pleural membranes are punctured, as occurs in penetrating trauma of the chest, air may travel from the lung to the muscles and subcutaneous tissue of the chest wall.^[5] When the alveoli of the lung are ruptured, as occurs in pulmonary laceration, air may travel beneath the visceral pleura (the membrane lining the lung), to the hilum of the lung, up to the trachea, to the neck and then to the chest wall.^[5] The condition may also occur when a fractured rib punctures a lung;^[5] in fact, 27% of patients who have rib fractures also have subcutaneous emphysema.^[6] Rib fractures may tear the parietal pleura, the membrane lining the inside of chest wall, allowing air to escape into the subcutaneous tissues.^[7]

Subcutaneous emphysema is a frequently found in pneumothorax (air outside of the lung in the chest cavity)^[8][9] and may also result from air in the mediastinum, pneumopericardium (air in the pericardial cavity around the heart).^[10] A tension pneumothorax, in which air builds up in the pleural cavity and exerts pressure on the organs within the chest, makes it more likely that air will enter the subcutaneous tissues through pleura torn by a broken rib.^[7] When subcutaneous emphysema results from pneumothorax, air may enter tissues including those of the face, neck, chest, armpits, or abdomen.^[11] When subcutaneous emphysema occurs with pneumomediastinum, the condition is known as Hamman's syndrome.^[12] Pneumomediastinum can result from a number of events. For example, foreign body aspiration, in which someone inhales an object, can cause pneumomediastinum (and lead to subcutaneous emphysema) by puncturing the airways or by increasing the pressure in the affected lung(s) enough to cause them to burst.^[2]

Subcutaneous emphysema of the chest wall is commonly among the first signs to appear that barotrauma, damage caused by excessive pressure, has occurred,^[11][13] and it is an indication that the lung was subjected to significant barotrauma.^[14] Thus the phenomenon may occur in diving injuries.^[3]

Trauma to parts of the respiratory system other than the lungs, such as rupture of a bronchial tube, may also cause subcutaneous emphysema.^[7] Air may travel upward to the neck from a pneumomediastinum that results from a bronchial rupture, or downward from a torn trachea or larynx into the soft tissues of the chest.^[7] It may also occur with fractures of the facial bones, neoplasms, during asthma attacks, when the Heimlich maneuver is used, and during childbirth.^[3] It is estimated to occur with pneumomediastinum in one in every 2000–100,000 deliveries.^[12] Injury with pneumatic tools, those that are driven by air, is also known to cause subcutaneous emphysema, even in extremities (the arms and legs).^[15] It can also occur as a result of rupture of the esophagus; when it does, it is usually as a late sign.^[16]

Medical Treatment[edit | edit source]

Subcutaneous emphysema is a common result of certain types of surgery; for example it is not unusual in chest surgery.^[17] It may also occur from surgery around the esophagus, and is particularly likely in prolonged surgery.^[18] Other potential causes are anesthesia, in which its occurrence is frequently unexpected,^[19] laparoscopy,^[18] and cricothyrotomy. In a pneumonectomy, in which an entire lung is removed, the remaining bronchial stump may leak air, a rare but very serious condition that leads to progressive subcutaneous emphysema.^[17] Air can leak out of the pleural space through an incision made for a thoracotomy to cause subcutaneous emphysema.^[17] On infrequent occasions, the condition can result from dental surgery, usually due to use of high-speed tools that are air driven.^[20] These cases result in usually painless swelling of the face and neck, with an immediate onset, the crepitus (crunching sound) typical of subcutaneous emphysema, and often with subcutaneous air visible on X-ray.^[20]

One of the main causes of subcutaneous emphysema, along with pneumothorax, is an improperly functioning chest tube.^[21] Thus subcutaneous emphysema is often a sign that something is wrong with a chest tube; it may be clogged, clamped, or out of place.^[21] The tube may need to be replaced, or, when large amounts of air are leaking, a new tube may be added.^[21]

Since mechanical ventilation can worsen a pneumothorax, it can force air into the tissues; when subcutaneous emphysema occurs in a ventilated patient, it is an indication that the ventilation may have caused a pneumothorax.^[21] It is not unusual for subcutaneous emphysema to result from positive pressure ventilation.^[22]

Another possible cause is a ruptured trachea.^[21] The trachea may be injured by tracheostomy or endotracheal intubation; in cases of tracheal injury, large amounts of air can enter the subcutaneous space.^[21] An endotracheal tube can puncture the trachea or bronchi and cause subcutaneous emphysema.^[4]

Infection[edit | edit source]

Air can be trapped under the skin in necrotizing infections such as gangrene, occurring as a late sign in gas gangrene,^[21] of which it is the hallmark sign. Subcutaneous emphysema is also considered a hallmark of fournier gangrene.^[23] Symptoms of subcutaneous emphysema can result when infectious organisms produce gas by fermentation. When emphysema occurs due to infection, signs that the infection is systemic, i.e. that it has spread beyond the initial location, are also present.^[5][15]

References[edit | edit source]

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