A pneumothorax is a condition in which air becomes trapped in the pleural space. This is usually caused by trauma to the lung, or a “punctured” lung. The patient continues to breathe, pulling air into the injured lungs, but the air escapes into the chest cavity. It cannot follow the path back up and out of the mouth as intended. As this air begins to accumulate, it causes pressure to build up inside the thorax. When pressure begins to affect other nearby organs, this is known as a tension pneumothorax. It is quite possible to have a punctured or collapsed lung without having a buildup of pressure- this is simply called a pneumothorax.