pneumothorax
(NOO-moh-THOR-ax)
An abnormal collection of air in the space between the thin layer of tissue that covers the lungs and the chest cavity. This can cause all or part of the lung to collapse. A pneumothorax may be caused by a chest injury, certain medical procedures, lung disease, or other damage to lung tissue. Sometimes the cause of a pneumothorax is not known. The most common symptoms are sudden chest pain and trouble breathing. Some types of pneumothorax may go away on their own, but others may be life threatening.