Primary spontaneous pneumothorax and subpleural blebs
A primary spontaneous pneumothorax is air in the pleural space (the gap between the lung and the chest wall) that occurs without injury, a medical procedure or known lung disease.
Remember
Think of a primary spontaneous pneumothorax in a tall, thin young person with healthy lungs and no injury, usually from rupture of small blebs (bubble-like swellings on the lung surface just under the pleura, the thin membrane covering the lung).
A pneumothorax is air in the pleural space, the gap between the lung and the chest wall. Pneumothoraces can be defined by their cause. In a primary spontaneous pneumothorax, spontaneous means it happens by itself, with no injury or medical procedure, and primary means the lungs were previously healthy.
It most commonly affects young, tall, thin males who have no lung disease and no injury. The usual explanation is the rupture of small subpleural blebs. Blebs are bubble-like swellings on the lung surface, and subpleural means just under the pleura, the thin membrane covering the lung. When one bursts, air leaks from the lung into the pleural space and the lung collapses.
Exactly how a primary spontaneous pneumothorax occurs is not fully understood. A burst can follow a small rise in pressure in the chest, for example during exercise, although it often happens at rest. Classically it presents with sudden pleuritic chest pain (sharp pain that is worse on deep breathing, coughing or sneezing), breathlessness and reduced breath sounds on the affected side.
The other types are also defined by their cause. A secondary spontaneous pneumothorax happens in a lung that is already diseased, for example by asthma. A traumatic pneumothorax follows an injury to the chest, and an iatrogenic one is caused by a medical procedure. Tension is different: it describes a dangerous state in which trapped air builds up pressure, so it is not a classification by cause.
Key facts
- Pneumothorax
- air in the pleural space, the gap between the lung and the chest wall.
- Primary
- the lungs were previously healthy, with no known lung disease.
- Spontaneous
- there was no injury or medical procedure.
- Who
- most commonly young, tall, thin males with no lung disease and no injury.
- Usual cause
- rupture of small subpleural blebs, bubble-like swellings just under the pleura.
- Secondary type
- happens in a lung that is already diseased, for example by asthma.
Exam traps
- A secondary spontaneous pneumothorax occurs when there is existing lung disease, such as asthma or cystic fibrosis, so it is not the label for a pneumothorax in a person with no lung disease.
- A traumatic pneumothorax follows an injury to the chest, such as a fractured rib, so it does not describe a pneumothorax that occurs with no injury.
- A spontaneous haemopneumothorax is a rare combination of air and blood in the pleural space, so it is not the best classification for a pneumothorax with no evidence of pleural bleeding.
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