A pneumothorax is commonly known as a collapsed lung. Normally, the outer surface of the lung sits next to the inner surface of the chest wall. The lung and the chest wall are covered by thin membranes called pleura.
A collapsed lung occurs when air escapes from the lungs or leaks through the chest wall and enters the space between the two membranes (pleural cavity). As air builds up, it causes the nearby lung to collapse.
A collapsed lung is most often caused by an injury to the lungs or chest wall, such as:
A penetrating injury, such as a knife or gunshot wound
Blunt trauma from a fall or car accident
Medical procedures, such as removal of fluid from the pleural cavity with a needle (thoracentesis) or a lung biopsy
Occasionally, a lung will collapse without any direct injury to the lung or chest. This is called a spontaneous pneumothorax. This is more likely to happen in people with lung disease.
It is particularly common in emphysema, which causes air-filled sacs, called blebs, to form. When one of these sacs bursts, air is released into the pleural cavity, causing the lung to collapse. It also occurs in people with asthma, cystic fibrosis and pneumonia.
A spontaneous pneumothorax also can develop in people who don't have any obvious lung disease. It's most common in tall, thin men between the ages of 20 and 40 and smokers.
In most cases of pneumothorax, some air can move in and out through the tear in the lung or chest wall. If air can only move into the chest cavity, but not out, pressure builds up inside the pocket of trapped air. This is called a tension pneumothorax.
A tension pneumothorax can cause complete collapse of the nearby lung and can push the heart and major blood vessels to the other side of the chest. This is a life-threatening emergency. Tension pneumothorax most commonly occurs in people with penetrating chest injuries.