Definition of Pneumomediastinum:

Pneumomediastinum is a condition in which air is present in the mediastinum (the space in the chest between the two lungs). This can be caused by a traumatic injury or disease.

Causes, incidence, and risk factors:

Pneumomediastinum is uncommon. It occurs when air leaks from any part of the lung or airways into the mediastinum.

One cause is when increased pressure within the lungs or airways ruptures the air sacs or airways, allowing air to escape into surrounding structures. Such pressure can be caused by excessive coughing, sneezing, vomiting or repeated Valsalva maneuvers (bearing down to increase abdominal pressure, such as during childbirth or defecation). It may also occur following perforation of the trachea (windpipe), rapid ascents in altitude, SCUBA diving, or use of a breathing machine (mechanical ventilation).

Pneumomediastinum also can occur in association with pneumothorax or other diseases.