Pneumothorax is defined as air in the pleural space and may be classified as spontaneous, traumatic or iatrogenic. Primary spontaneous pneumothorax may occur in patients without clinically apparent lung disease. Secondary spontaneous pneumothorax is a complication of pre-existing lung disease.1 Primary pneumothorax typically occurs in tall, thin males between 10 to 30 years of age. It has a recurrence rate of approximately 30 per cent.1 The incidence of secondary spontaneous pneumothorax is similar to that of primary spontaneous pneumothorax. However, the peak incidence of secondary pneumothorax occurs between 60 and 65 years of age.
Smoking increases the risk of pneumothorax in a dose-dependent manner.
Subpleural blebs and bullae are likely to play a role in the pathogenesis. They are found in up to 90 per cent of cases of primary pneumo- thorax at thoracoscopy or thoraco- tomy and in up to 80 per cent of cases following CT scanning of the chest.2 The gradient in pleural pressure increases from the lung base to the apex, therefore alveoli at the lung apex in tall individuals are subject to a greater distending pressure than those at the base of the lung. This means there is an increased risk of developing subpleural blebs. The mechanism of bulla formation is unclear.