Causes of Subcutaneous Emphysema
Subcutaneous emphysema results from air entering the subcutaneous tissues through disruption of air-containing structures, most commonly from tracheal/bronchial injury, pneumothorax, or iatrogenic causes during medical procedures.
Primary Mechanisms and Causes
Traumatic Causes
The most common traumatic etiology is tracheal and bronchial rupture, which rapidly produces mediastinal emphysema and subcutaneous emphysema in the suprasternal fossa that spreads to the neck, face, and chest 1. Both penetrating and blunt trauma can cause these injuries, leading to the typical manifestations of tracheal injury with gas collection along the anterior spine and severe mediastinal gas accumulation 1.
Iatrogenic Causes
Chest tube drainage complications represent a major iatrogenic source, occurring through several mechanisms 2:
- Poor tube placement or anchorage
- Tube blockage leading to increased intrathoracic pressure
- Side-port migration into subcutaneous tissue
- Malpositioned, kinked, or clamped tubes
Dental procedures have emerged as an increasingly recognized cause, with a significant rise in cases over time 3. The primary culprits are:
- Air-driven handpieces during dental extractions (51% of cases)
- Air syringes (9% of cases)
- Surgical extractions of posterior mandibular teeth carry the highest risk
- Air injection under pressure into tissues 4
Other iatrogenic causes include central line insertion, positive pressure ventilation, and various surgical procedures involving the aerodigestive tract 5, 4.
Pulmonary and Airway Pathology
Pneumothorax is frequently associated with subcutaneous emphysema, particularly when:
- Large or bilateral pneumothoraces are present
- Bronchopleural fistulae exist
- Mechanical ventilation creates pressure gradients 2
Alveolar rupture allows air to enter pulmonary veins and track along fascial planes into subcutaneous tissues 5.
Infectious Causes
Gas-forming organisms in necrotizing soft tissue infections can produce subcutaneous emphysema 6, 7. Gas in deep fascial planes is a hallmark of necrotizing fasciitis and represents a surgical emergency 7, 8.
Anatomical Considerations
A continuum of fascial planes connects cervical soft tissues with the mediastinum and retroperitoneum, permitting air from any of these areas to spread elsewhere 9. This explains why air can track extensively from a single point of origin.
Clinical Context-Specific Causes
In trauma patients: Look for tracheal/bronchial injury, pneumothorax, or esophageal perforation 1, 5.
Post-chest tube insertion: Consider tube malposition, blockage, or side-port migration—these are avoidable causes associated with increased morbidity and mortality 2.
Following dental work: Suspect air-driven handpiece use during extractions, especially of lower molars 3.
With mechanical ventilation: Barotrauma from positive pressure creates pressure gradients favoring air dissection into tissues 9, 4.
Spontaneous cases: Consider underlying pulmonary disease, coughing, or Valsalva maneuvers that increase intra-alveolar pressure 9.
Critical Pitfalls
The presence of subcutaneous emphysema itself is not dangerous, but failure to recognize the underlying cause is the primary hazard 9. Certain trauma-related causes require immediate surgical intervention, particularly tracheal/bronchial rupture or necrotizing fasciitis 1, 7.
Avoid routine use of tracheostomy or mediastinal drains for subcutaneous emphysema alone—treat the underlying cause 9. However, when subcutaneous emphysema develops with chest tube drainage and worsens despite intervention, urgent tube replacement may be necessary 2.
In rare factitious cases, patients may self-inject air—examine for puncture marks when presentation is unexplained and recurrent 10.