A pneumothorax, often called a “collapsed lung,” occurs when air accumulates in the space between the lung and the chest wall, known as the pleural space. This abnormal collection of air exerts pressure on the lung, preventing it from fully expanding with each breath. A spontaneous pneumothorax specifically refers to this condition happening without any external injury or medical procedure. Instead, it arises unexpectedly from internal factors within the body.
Types of Spontaneous Pneumothorax
Spontaneous pneumothorax is categorized into two main types: primary and secondary. Primary spontaneous pneumothorax (PSP) develops in individuals who do not have any known underlying lung disease. This type typically affects younger, often tall and thin, males between 10 and 30 years old.
In contrast, secondary spontaneous pneumothorax (SSP) occurs in individuals who already have a pre-existing lung condition. SSP is more common in older individuals, with a peak incidence observed between 60 and 64 years of age.
Causes of Primary Spontaneous Pneumothorax
The primary cause of primary spontaneous pneumothorax (PSP) is the rupture of small, air-filled sacs on the lung surface called blebs or bullae. These blebs and bullae are essentially weakened areas of lung tissue. Their rupture allows air to leak from the lung directly into the pleural space.
While the exact reason for their formation and rupture is not fully understood, these structures are often present in individuals without overt lung disease.
Causes of Secondary Spontaneous Pneumothorax
Secondary spontaneous pneumothorax (SSP) arises as a complication of various underlying lung diseases that compromise lung tissue integrity. Chronic Obstructive Pulmonary Disease (COPD), particularly with emphysema, is a frequent cause, as the damaged air sacs can rupture and release air into the pleural space. Cystic fibrosis also predisposes individuals to SSP due to mucus buildup and recurrent infections that damage lung tissue. Asthma, a chronic inflammatory airway disease, can also contribute to lung vulnerability.
Lung infections, such as pneumonia and tuberculosis, can weaken lung tissue, increasing the risk of air leakage. Lung cancer, whether primary or metastatic, can also lead to SSP by directly damaging lung structures or causing the rupture of compromised areas. Interstitial lung diseases, which involve scarring and inflammation of lung tissue, make the lungs less elastic and more prone to collapse. Connective tissue disorders, such as Marfan syndrome, Ehlers-Danlos syndrome, and Birt-Hogg-Dubé syndrome, are also linked to SSP due to their impact on lung structural proteins. Other conditions like Alpha-1 antitrypsin deficiency and Lymphangioleiomyomatosis also weaken lung structure, increasing the risk of SSP.
Factors Increasing Risk
Several factors can increase an individual’s susceptibility to developing either primary or secondary spontaneous pneumothorax. Smoking is a significant risk factor for both types, with the risk increasing considerably with the duration and amount of smoking. For instance, the lifetime risk of spontaneous pneumothorax in heavy-smoking men is estimated to be approximately 12 percent, compared to only 0.1 percent in non-smokers.
Body habitus also plays a role, with tall and thin individuals having a higher likelihood of experiencing primary spontaneous pneumothorax. Genetic predisposition is another factor, as spontaneous pneumothorax can cluster in families.
A previous history of spontaneous pneumothorax significantly increases the risk of recurrence, with rates up to 43% for SSP. Changes in atmospheric pressure, such as those experienced during diving or flying, or during rapid weather shifts, may also act as potential triggers for pneumothorax in predisposed individuals, though they are not direct causes. Such pressure variations can influence transpulmonary pressure.