Pneumothorax is defined as the air in pleural cavity. Pleural cavity normally does not contain any air.
It could be either primary or secondary.
A primary pneumothorax is one that occurs without an apparent cause and in the absence of significant lung disease, while a secondary pneumothorax occurs in the presence of pre-existing lung pathology.
In addition, pneumothorax is of following types
The opening in the lung leading to air in the pleural cavity is very small and heals very rapidly. This allows the lung to re-expand.
In such cases, the opening in the lung remains patent leading to air in the pleural cavity at a pressure equal to atmospheric pressure.
Tension pneumothorax occurs in valvular openings. In such cases, the air enters the pleural cavity during inspiration but cannot escape during expiration due to closure of the opening [Due to its valvular nature].
This leads to positive pressure in the pleural cavity. Tension pneumthorax needs to be attended on emergency basis.