Pneumomediastinum

Basics

Description

  • 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

Etiology

  • 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

There's more to see -- the rest of this topic is available only to subscribers.