• What is it:
  • Pneumomediastinum is the presence of air or gas within the mediastinum.
  • It occurs due to the rupture of air-containing structures (e.g., alveoli, trachea, esophagus) or direct introduction of air from trauma or procedures.
• Etymology:
  • Derived from the Greek words pneuma (air) and mediastinum (middle compartment), it describes air accumulation in the central thoracic space.
• AKA:
  • Mediastinal emphysema.
• How does it appear on each relevant imaging modality:
  • Chest X-ray:
    • Air outlines mediastinal structures, such as the heart, great vessels, and pericardium.
    • Lucent streaks of gas may appear along the cardiac border or the superior mediastinum.
    • The “continuous diaphragm sign” may be present when air outlines the central diaphragm beneath the heart.
  • Chest CT (preferred):
    • Parts: Air pockets in the mediastinum without mass effect.
    • Size: Variable; large pneumomediastinum may compress mediastinal structures.
    • Shape: Irregular or streaky lucencies outlining mediastinal structures.
    • Position: Air is often found along the anterior mediastinum, trachea, esophagus, or vascular structures.
    • Character: Sharp outlines of mediastinal structures due to air contrast; may coexist with subcutaneous emphysema or pneumothorax.
  • Ultrasound:
    • Rarely used; may show reverberation artifacts (ring-down or comet-tail artifacts) due to air.
• Differential diagnosis:
  • Trauma: Blunt or penetrating chest trauma, esophageal rupture (Boerhaave syndrome).
  • Iatrogenic: Tracheal intubation, esophageal instrumentation, or chest surgery.
  • Spontaneous: Rupture of alveoli with air tracking along bronchovascular sheaths (Macklin effect).
  • Infectious: Gas-forming mediastinitis (e.g., from esophageal perforation).
  • Other causes: Valsalva maneuvers (e.g., forceful vomiting, coughing, childbirth).
• Recommendations:
  • Further evaluation:
    • Contrast esophagography or CT with oral contrast if esophageal rupture is suspected.
    • Bronchoscopy if tracheobronchial injury is a concern.
  • Clinical correlation:
    • Assess for symptoms such as chest pain, dyspnea, or subcutaneous emphysema.
    • Consider recent trauma, surgical history, or vigorous activities.
  • Management:
    • Observation for mild, asymptomatic cases of spontaneous pneumomediastinum.
    • Emergency intervention (e.g., thoracic surgery) for tension pneumomediastinum or esophageal rupture.
• Key considerations and pearls:
  • Pneumomediastinum is often self-limiting when spontaneous but may signal severe underlying pathology (e.g., Boerhaave syndrome).
  • The Macklin effect explains how alveolar rupture leads to air dissection into the mediastinum, often seen on CT.
  • Always evaluate for associated findings such as pneumothorax, subcutaneous emphysema, or pneumopericardium.
  • The presence of mediastinal air without trauma or infection often resolves with conservative management, including oxygen therapy to accelerate air reabsorption.

This structured approach highlights the key imaging features, differential diagnoses, and management considerations for pneumomediastinum.

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