Bullae formation hypothesis in primary spontaneous pneumothorax

Primary spontaneous pneumothorax (PSP) typically occurs in tall and thin subjects without clinically apparent underlying lung disease (1). The incidence of PSP has geographical and gender-based differences. In the United States, 7.4 cases (age-adjusted incidence) per 100,000 population develop annually in males and 1.2 cases per 100,000 population per year in females (2). In the United Kingdom, 37 cases per 100,000 population develop annually in males and 15.4 cases per 100,000 population per year in females (3). The reasons for these differences are still unknown. The most common cause of a PSP is the rupture of small subpleural bleb/bullae (4). Subpleural bullae are found in most patients during thoracoscopy or thoracotomy (5). However, it remains uncertain how the bullae, the key of pathogenesis for PSP, have been formed in the young, healthy lungs