Pneumomediastinum

Basics

Presence of free air or gas within the mediastinum (mediastinal emphysema)
May originate from esophagus, alveolar, or bronchial tree (aerodigestive process)
May occur spontaneously (primary pneumomediastinum) or as result of trauma, surgery, or other pathologic processes (secondary pneumomediastinum)
Spontaneous pneumomediastinum:
- Caused by extrapleural tracheobronchial injury:
  - Increased intra-alveolar pressure, low perivascular pressures, or both
  - Terminal alveolar rupture into the lung interstitium and bronchovascular tissue sheath
  - Dissection of air into the hilum and subsequently the mediastinum along a pressure gradient
  - Mediastinal air then dissects into the fascial planes, most commonly into the tissues of the neck
- Often in setting of a Valsalva maneuver, forceful vomiting, in association with bronchospasm (i.e., asthma exacerbations) or inhalational drug use
- Men > women (2:1 in some series)
- Young > old (most common in second/third decades of life in most series)
- Rare in pediatric patients, but with a bimodal age distribution of peak incidence (<7 and 13–17 yr)
Relatively rare, 1/30,000–50,000 hospital admissions

Primary or spontaneous pneumomediastinum:
- Associated with forced Valsalva maneuvers:
  - Forceful vomiting
  - Forceful straining during exercise
  - Straining during defecation
  - Coughing/sneezing
  - Intense screaming
  - Labor and delivery
  - Playing wind instruments
  - Pulmonary function testing
  - Anorexia nervosa
  - Obesity
  - Pre-existing lung disorders (interstitial lung disease, pulmonary fibrosis, pneumonitis)
  - Illicit inhalation drug use (marijuana, cocaine, methamphetamine)
  - Tobacco abuse
  - Rapid ascent in scuba divers
- A majority of cases will have no identified precipitating event/cause
- Has been rarely described after dental extraction/procedures
Secondary pneumomediastinum:
- Secondary to thoracic barotrauma
- Blunt trauma is the most common mechanism
- Common traumatic mechanisms:
  - Motor vehicle collision
  - Fall
  - Blows to chest or neck
  - Open facial/neck injury
  - Recent esophageal/tracheobronchial instrumentation/endoscopy
- Positive-pressure mechanical ventilation
- Esophageal rupture (Boerhaave syndrome)
- In association with mediastinal infection caused by gas-forming organisms
Tension pneumomediastinum:
- Rare but life-threatening event
- Usually in patients on positive-pressure ventilation
May be associated with pneumopericardium and/or extension of a pneumothorax/tension pneumothorax

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