Pneumomediastinum

Basics

Description

  • Presence of free air or gas within the mediastinum (mediastinal emphysema)
  • May originate from esophagus, alveolar, or bronchial tree (aerodigestive process)
  • Can be spontaneously (primary pneumomediastinum) or as result of trauma, surgery, infection, or other pathologic processes (secondary pneumomediastinum)
  • Spontaneous pneumomediastinum:
    • 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 dissects into fascial planes, most commonly the tissues of the neck
    • Men > women (2:1 in some series)
    • Young > old (most common in 2nd/3rd decades of life)
    • Rare in pediatric patients, but with a bimodal age distribution of peak incidence (<7 yr and 13–17 yr)
  • Relatively rare, 1/30,000–50,000 hospital admissions

Etiology

  • Primary or spontaneous pneumomediastinum:
    • Associated with forced Valsalva maneuvers (most common):
      • Vomiting and straining
      • Coughing and bronchospasm (ie, asthma)
      • Intense screaming
      • Labor and delivery
      • Playing wind instruments
      • Pulmonary function testing
      • Anorexia nervosa
      • Obesity
      • Preexisting lung disorders (ILD, pulmonary fibrosis, pneumonitis)
      • Illicit inhalation drug use (marijuana, cocaine, methamphetamine)
      • Tobacco abuse
      • Improper decompression/ascent in scuba divers
    • A majority of cases will have no identified precipitating event/cause
    • Has been rarely described after dental
    • extraction/procedures
    • COVID-19 has a 65% increase
    • incidence of Pneumomediastinum, in some studies
    • Generally caused by the Macklin effect, a three step process:
      • Blunt traumatic alveolar rupture
      • Air dissects along bronchovascular sheaths
      • Spreading of the emphysema into the mediastinum
    • When the Macklin effect is noted, esophageal rupture can be ruled out
  • 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 ventilation (PPV)
    • 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 PPV
  • May be associated with pneumopericardium and/or extension of a pneumothorax (PTX)/tension PTX

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