Pneumothorax is the presence of air within the pleural space, the potential space between the lung and the inner chest wall, resulting in partial or complete loss of the normal negative pressure that helps keep the lung expanded. As air accumulates, the affected lung can collapse to varying degrees. A Pneumothorax may occur spontaneously without an obvious external injury, develop because of underlying lung disease, or result from trauma or medical procedures. A primary spontaneous Pneumothorax occurs without recognised underlying lung disease, often in otherwise healthy people, whereas a secondary spontaneous Pneumothorax occurs in association with conditions that have altered lung structure. Traumatic and iatrogenic forms have distinct mechanisms and management considerations.
In a healthy thorax, the pleural space contains only a very small amount of lubricating fluid and maintains subatmospheric pressure relative to the alveoli. This pressure relationship allows the elastic tendency of the lung to recoil inward to be balanced by outward recoil of the chest wall. When air enters the pleural space, the pressure gradient is disrupted and the lung recoils away from the chest wall.
The degree of collapse depends on the volume and rate of air entry, the elasticity of the lung, the presence of pleural adhesions and other anatomical factors. If air continues to enter the pleural space under pressure without adequate escape, a tension Pneumothorax can develop, causing increasing intrathoracic pressure, compression of the lung and impaired venous return to the heart.
Primary spontaneous Pneumothorax is often associated with rupture of small subpleural blebs or areas of abnormal lung architecture, although the exact cause is not always identifiable. It occurs more frequently in certain demographic groups and is strongly associated with cigarette smoking, which increases risk. Secondary Pneumothorax can complicate conditions such as emphysema, severe asthma, Cystic Fibrosis, tuberculosis and other structural lung disorders.
Trauma can cause air to enter through penetrating or blunt injury, while medical procedures involving the chest, central venous access or lung tissue can occasionally produce an iatrogenic Pneumothorax. Mechanical ventilation is a particular risk because positive pressure can force air through damaged or vulnerable alveoli into surrounding tissues and ultimately the pleural space.
Symptoms depend on the size of the Pneumothorax, its rate of development and the person's underlying respiratory reserve. Sudden unilateral chest pain and breathlessness are characteristic, although some small Pneumothoraces produce few symptoms and may be discovered incidentally. Examination can reveal reduced breath sounds or altered percussion over the affected side, but these findings can be subtle, especially in small Pneumothoraces. Tension Pneumothorax is a medical emergency and can cause severe breathlessness, hypotension, tachycardia, impaired consciousness and cardiovascular collapse.
The classical physical signs of tracheal deviation or distended neck veins are not necessarily present early and should not be required before emergency treatment. In a deteriorating patient with a strong clinical suspicion of tension physiology, treatment should not be delayed solely to obtain imaging.
Chest radiography is commonly used to identify a Pneumothorax, with visible pleural air and a retracted lung edge often demonstrating the diagnosis. Computed tomography can detect very small or loculated collections of pleural air and may be useful when the diagnosis is uncertain or additional thoracic pathology needs evaluation. Bedside ultrasound can also detect features associated with Pneumothorax and is particularly useful in emergency and critical-care settings.
The size of a Pneumothorax can be estimated in different ways depending on the imaging modality and clinical protocol, but management should not be based solely on a numerical size because symptoms, physiological stability, underlying disease and cause are also important. A small Pneumothorax in a stable person with healthy lungs can have a very different clinical significance from a similarly sized Pneumothorax in someone with severe underlying lung disease.
Management ranges from observation to aspiration, chest-drain insertion or surgery depending on the type and clinical circumstances. Some stable, minimally symptomatic Pneumothoraces can be managed conservatively with observation and follow-up, allowing the pleural air to be reabsorbed naturally. Others require active removal of air using needle aspiration or a chest tube connected to an appropriate drainage system. Tension Pneumothorax requires immediate decompression, generally followed by definitive pleural drainage.
Recurrent Pneumothorax may lead to consideration of procedures designed to prevent further episodes, such as surgical repair of identifiable blebs or bullae and pleural interventions that promote adhesion between the pleural surfaces. Management is therefore individualised according to recurrence risk, cause, physiological stability and available expertise.
Recurrence is an important feature of spontaneous Pneumothorax, particularly when the underlying structural predisposition remains. Smoking cessation can substantially reduce recurrence risk and is an important intervention for smokers. People with repeated episodes or particular occupational, recreational or travel circumstances may receive specialist advice concerning air travel and activities involving major pressure changes, because changes in ambient pressure can enlarge trapped pleural air.
Scuba diving presents a separate and potentially serious risk because compressed-gas exposure can create dangerous pressure changes, and people with a history of Pneumothorax require specialist assessment before considering return to diving. Follow-up imaging may be used to confirm resolution. The presence of underlying lung disease can increase both the immediate severity of an episode and the likelihood that more definitive treatment will be needed.
A common misconception is that every Pneumothorax causes complete lung collapse or that any chest pain automatically indicates one. Pneumothoraces range from tiny, clinically silent collections to life-threatening tension physiology. Another important distinction is between ordinary Pneumothorax and tension Pneumothorax: the latter is defined by progressive pressure effects on thoracic structures and circulation rather than simply by the size of the air collection. Pneumothorax also differs from pleural effusion, in which fluid rather than air accumulates in the pleural space. Its importance lies in the mechanical relationship between the lung, pleural space and cardiovascular system, which explains why an apparently localised air leak can sometimes become an immediate threat to breathing and circulation.
