Subcutaneous emphysema (SE) is the presence of air trapped beneath the skin, specifically within the subcutaneous tissue layer. This condition is not a disease but a sign that air has escaped from an internal organ or external source and collected in the body’s soft tissues. The most recognizable symptom is a distinctive crackling sensation, known as crepitus, when the affected area is gently pressed. While SE often resolves spontaneously as the body absorbs the trapped air, its presence signals an underlying issue that requires medical evaluation.
The Underlying Mechanism of Air Migration
The movement of air into the subcutaneous space is governed by a positive pressure gradient. Air escapes from a high-pressure source, such as the lungs or a ruptured airway, into a lower-pressure area like the loose connective tissues beneath the skin. This air travels along the body’s fascial planes, which are layers of connective tissue that separate and surround muscles and organs.
These planes offer paths of least resistance for gas to travel. When a leak occurs in the chest, air often first accumulates in the mediastinum, a condition called pneumomediastinum. From this central location, air tracks upward into the neck. Because the subcutaneous tissue of the neck and chest is particularly loose, the air spreads easily, leading to the characteristic swelling that defines subcutaneous emphysema.
Primary Causes: Leakage from the Chest and Lungs
The most frequent sources of subcutaneous emphysema involve the lungs and chest cavity. A common cause is pneumothorax, where air leaks from the lung surface into the pleural space. If this air breaches the chest wall, it escapes into the surrounding soft tissues, manifesting as subcutaneous emphysema.
Traumatic injuries to the chest are a major pathway for air to escape. Examples include rib fractures, which can puncture the lung tissue, and penetrating wounds from stabbing or gunshot. Similarly, blunt force trauma can rupture a bronchus, allowing a substantial volume of air to leak out rapidly.
Iatrogenic and Pressure-Related Causes
Certain medical procedures and interventions are also frequent causes, often referred to as iatrogenic causes. Air leakage can occur following chest surgery, such as a thoracotomy, or due to complications associated with chest tube insertion. Barotrauma, injury caused by excessive pressure, leads to alveolar rupture in the lungs, forcing air into the chest cavity and then subcutaneously. This is often seen in patients on mechanical ventilation or after severe coughing fits in those with underlying lung conditions.
Secondary Causes: Trauma and Procedures Affecting the Head and Neck
Subcutaneous emphysema can also originate from leaks in the airway or sinuses located in the head and neck. Procedures that directly involve the upper airway pose a risk, such as a tracheostomy or traumatic intubation. These procedures can cause a tear in the trachea, allowing air to escape into the neck tissues.
Trauma to the face and neck, including fractures of the facial bones or the larynx and trachea, can introduce air into the soft tissues. Air from the sinuses can be forced into the subcutaneous layer following a fracture. Additionally, certain dental or oral surgical procedures can be implicated, particularly when pressurized air is used, which inadvertently forces air into the surrounding soft tissues.
Identifying and Treating Subcutaneous Emphysema
Diagnosis begins with a physical examination when a healthcare provider palpates the skin and detects crepitus. This clinical finding is confirmed using imaging studies to visualize the trapped air pockets. A chest X-ray or Computed Tomography (CT) scan clearly shows the presence of air in the soft tissues, helping to map its extent and identify the source of the leak.
Management focuses entirely on addressing the underlying cause of the air leak. The trapped air is gradually reabsorbed by the body over days to weeks once the source has been sealed. Treatment involves interventions like inserting a chest tube to manage a pneumothorax or repairing a traumatic tear in the airway. In rare, severe instances where swelling compromises breathing or circulation, a provider may create small incisions or insert catheters to manually release the trapped air and relieve pressure.