Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online.In medicine (pulmonology), a pneumothorax is a potential medical emergency wherein air or gas is present in the pleural cavity. A pneumothorax can occur spontaneously. It can also occur as the result of disease or injury to the lung, or due to a puncture to the chest wall. A pneumothorax can result in a collapsed lung, or can be created therapeutically to collapse a lung. Pneumothoraces are divided into tension and non-tension pneumathoraces. A tension pneumothorax is a medical emergency as air accumulates in the pleural space with each breath. The increase in intrathoracic pressure results in massive shifts of the mediastinum away from the affected lung compressing intrathoracic vessels.