Alveolar Rupture

Tracheobronchial Injury

Esophageal Injury

Iatrogenic Injury

Extension from Neck or Abdomen

Mediastinitis (Rare)

Alveolar rupture due to asthma, coughing, Valsalva maneuver, volutrauma, alveolar lung disease, or interstitial lung disease

Iatrogenic injury due to chest tube placement or tracheostomy

Ectopic gas in mediastinum; often clinically evident

Lucency along heart border that often extends into neck; lucent regions around mediastinal structures

Continuous diaphragm sign: Gas outlines inferior aspect of heart (also in pneumopericardium)

Pneumothorax in other portions of pleural space

If not loculated, will rapidly shift with change in position

Lacks distinct pleural line of pneumomediastinum

Artifact no longer apparent when excluding dense heart from field of vision

Does not extend above level of hila; continuous diaphragm sign

Rapidly shifts with change in position

Lacks distinct pleural line of pneumomediastinum; may see indistinct black line (gas in skin fold)

Often nonanatomic orientation; disappears on repeat studies

Small gas-filled foci at thoracic inlet along right posterolateral aspect of trachea

Connection to trachea rarely seen