Pneumomediastinum may be classified according to cause into spontaneous pneumomediastinum and secondary pneumomediastinum. Both the categories have multiple causes.

Pneumomediastinum is mainly classified according to the cause into 2 groups^[1]:

• Spontaneous, also known as idiopathic pneumomediastinum: Cause of sponateous pneumomediastinum is use of tobacco and recreational drugs such as cocaine, marijuana, methamphetamine.
• Secondary pneumomediastinum:
  • Iatrogenic: Endoscopic procedures, intubation/extubation, central vascular access procedure, pleural cavity instrumentation, chest or abdominal surgery.
  • Traumatic: Blunt force trauma, penetrating chest or abdominal injury.
  • Non-traumatic: Predisposing factors are preexisting medical conditions such as asthma, interstitial lung disease, COPD, bronchiectasis, lung cysts, lung malignancy, excessive vomiting.

• Pneumomediastinum can also be classified according to the entry of air into the mediastinal cavity: Head/neck/upper respiratory tract, lower respiratory tract, lungs, gastrointestinal tract, or external environment. ^[2]