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.

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.

Pneumomediastinum may not be accompanied by any symptoms. Usually, it causes severe chest pain below the sternum (breastbone) that may radiate to the neck or arms. The pain may be worse with breathing or swallowing.

During a physical examination, the doctor may feel small bubbles of air under the skin of the chest, arms, or neck. A chest x-ray or CAT scan of the chest may be done to confirm the presence of air in the mediastinum.

Often, no treatment is required as the air is gradually absorbed from the mediastinum. If pneumomediastinum is accompanied by pneumothorax, a chest tube may be placed. Breathing high concentrations of oxygen may allow the air in the mediastinum to be absorbed more quickly.

The outlook depends on the disease or events that caused the pneumomediastinum.

In rare cases, so much air may accumulate in the mediastinum that veins are compressed, leading to low blood pressure.

Go to the emergency room or call the local emergency number (such as 911) if you have severe chest pain or difficulty breathing.