In some cases, the visceral pleura remains intact, but alveolar gas gains entry to the pleural space via the mediastinum. When perivascular alveoli rupture, alveolar gas can dissect centripetally along the bronchovascular interstitium to the mediastinum, entering the pleural space through the mediastinal parietal pleura. A commonly used classification of pneumothorax recognizes traumatic pneumothorax and iatrogenic pneumothorax as distinct clinical entities and lumps all other causes of pneumothorax under the somewhat misleading label of spontaneous pneumothorax. When spontaneous pneumothorax occurs in patients with underlying pleural or parenchymal disease, it is called secondary spontaneous pneumothorax. When no underlying lung disease is evident, it is called idiopathic spontaneous pneumothorax.
Patients often have a tall, thin stature and very frequently are cigarette smokers.
The precise mechanism whereby male sex, asthenic habitus, and cigarette smoking predispose to apical pleural bleb formation or rupture is unknown. One study detected anomalies of the bronchial tree in the majority of patients with spontaneous pneumothorax, suggesting associated congenital abnormalities of lung structure. How these anomalies may relate to the occurrence of pneumothorax is unclear. Common misconceptions are that strenuous physical activity is frequently a trigger for the development of pneumothorax and that patients are at increased risk during airplane travel. The most common symptoms of pneumothorax are chest pain and dyspnea.