Definition of Pneumomediastinum:

Pneumomediastinum is air in the mediastinum. The mediastinum is the space in the middle of the chest, between the lungs.

Causes, incidence, and risk factors:

Pneumomediastinum is uncommon. The condition can be caused by injury or disease. Most often, it occurs when air leaks from any part of the lung or airways into the mediastinum.

Increased pressure in the lungs or airways may be caused by:

• Excessive coughing
• Repeated bearing down to increase abdominal pressure (such as pushing during childbirth or a bowel movement)
• Sneezing
• Vomiting

It may also happen after:

• Rapid rises in altitude, SCUBA diving
• Tearing of the esophagus (the tube that connects the mouth and stomach)
• Tearing of the trachea (windpipe)
• Use of a breathing machine
• Using inhaled recreational drugs such as crack cocaine

Pneumomediastinum also can occur with pneumothorax or other diseases.