**1. Background**

Pneumothorax is a diverse entity with a wide array of clinical etiologies. It is more common in men than women [1–4]. Although pneumothorax can be defined simply as an abnormal collection of air in the pleural space, in order to accurately classify pneumothorax, it is helpful to group it broadly as either spontaneous or traumatic in nature [1, 2]. Overall, traumatic causes of pneumothorax account for greater than 50% of pneumothoraces on an annual basis [3]. These include injuries due to either true penetration or blunt traumatic events, including gunshot wounds, stabbings, blunt force trauma to the chest, or iatrogenic traumas sustained as part of medical procedures, such as central venous catheter placement, needle biopsies, and thoracentesis. Outside of trauma, the remainders of pneumothoraces are classified as spontaneous in nature. Although spontaneous pneumothorax accounts for less than half of all pneumothoraces, this type of pneumothorax is often the one that most demands the ongoing attention of the thoracic surgeon in the acute setting.

Spontaneous pneumothorax is itself classified into primary and secondary etiologies. Primary spontaneous pneumothorax is any pneumothorax that occurs without any identifiable inciting event in a patient without any known lung disease. Secondary spontaneous pneumothorax, on the other hand, defines any pneumothorax that develops in a patient as a complication of known underlying lung disease. Many diseases of the lung parenchyma can cause clinical pneumothorax; those

## *Pneumothorax*

**Figure 1.** *Subpleural blebs of the apical lung with adhesion to the chest wall.*

most commonly associated with its development include necrotizing pneumonias, cystic fibrosis, chronic obstructive pulmonary disease, and malignancy. Chronic obstructive pulmonary disease is the cause of 50–70% of all secondary spontaneous pneumothoraces. Catamenial pneumothorax is a very interesting clinical entity that is another, although rare, type of secondary spontaneous pneumothorax.

It is important to note that despite the definition of primary spontaneous pneumothorax indicating that it occurs in the setting of patients with no known lung disease, this is not completely clinically accurate. The majority of these patients do in fact have underlying lung disease with subpleural blebs (**Figure 1**), and it is the spontaneous rupture of these blebs that leads to the development of their pneumothoraces [3]. Despite a wide array of potential clinical etiologies, the overall incidence of spontaneous pneumothorax has been estimated at 17–24/100,000 in males and 1–6/100,000 in the female population [1–3]. Smoking increases the risk of contracting a first pneumothorax approximately 9-fold among women and 22-fold among men [5]. Spontaneous pneumothorax recurrence rates were similar for both men and women, with approximately 26% of patients experiencing a recurrence within 5 years of initial pneumothorax diagnosis [6].
