Pneumothorax

A pneumothorax is the presence of air in the pleural space — the gap between the lung and the chest wall — which breaks the normal negative pressure that holds the lung expanded and allows the lung to collapse partially or completely. It ranges from a small, self-limited collection to a life-threatening tension pneumothorax that compresses the heart and great vessels.

Definition

A pneumothorax is an abnormal collection of air in the pleural cavity, resulting in loss of the negative pleural pressure that normally keeps the lung apposed to the chest wall and producing partial or complete lung collapse.

Scope

This topic covers what a pneumothorax is, how it is classified (spontaneous versus traumatic or iatrogenic, primary versus secondary, and the special category of tension pneumothorax), the mechanism by which air enters the pleural space, and the conceptual basis of its evaluation. It is a reference and educational entry and does not provide management thresholds or procedural instructions for an individual patient.

Core questions

• Is the pneumothorax spontaneous, traumatic, or iatrogenic?
• Is it primary (no apparent lung disease) or secondary (underlying lung disease)?
• Is there physiological compromise suggesting a tension pneumothorax?
• What imaging confirms the presence and extent of pleural air?

Key concepts

• Air in the pleural space and loss of negative pleural pressure
• Primary spontaneous pneumothorax
• Secondary spontaneous pneumothorax
• Traumatic and iatrogenic pneumothorax
• Tension pneumothorax
• Subpleural blebs and bullae
• Chest radiography and thoracic ultrasound
• Needle aspiration and intercostal chest drainage

Mechanisms

The pleural space normally carries a small negative pressure that keeps the elastic lung expanded against the chest wall. When a communication opens between the airways or alveoli and the pleural space (as with rupture of a subpleural bleb), or between the pleural space and the outside air (as with a penetrating chest wound), air enters and the pleural pressure rises toward atmospheric; the lung's elastic recoil then pulls it inward and it collapses. Primary spontaneous pneumothorax characteristically arises from rupture of small subpleural blebs in otherwise healthy, often tall and thin, individuals, whereas secondary spontaneous pneumothorax complicates underlying lung disease such as chronic obstructive pulmonary disease. A tension pneumothorax develops when a one-way valve mechanism lets air accumulate progressively under positive pressure, shifting mediastinal structures and impairing venous return and cardiac output.

Clinical relevance

Pneumothorax is a recognisable cause of acute breathlessness and pleuritic chest pain, and tension pneumothorax is a physiological emergency that the concept exists in part to highlight. This entry describes how pneumothorax is categorised and understood for reference and education; it is not a source of decision rules for observation, aspiration, or drainage in a specific patient.

Epidemiology

Primary spontaneous pneumothorax occurs most often in younger people, with a marked male predominance, and is strongly associated with smoking; secondary spontaneous pneumothorax occurs in older people with established lung disease and carries a worse prognosis. Iatrogenic pneumothorax, for example after central line insertion or lung biopsy, is an additional important cause whose frequency reflects procedural practice.

Evidence & guidelines

The British Thoracic Society pleural disease guideline on spontaneous pneumothorax (MacDuff et al., 2010) and the companion guidance on pleural procedures and thoracic ultrasound (Havelock et al., 2010) summarise long-standing practice. More recent randomised evidence, notably the conservative-versus-interventional trial of Brown et al. (2020), has prompted reassessment of how some uncomplicated primary spontaneous pneumothoraces are approached. Guidance evolves and is described here for orientation only, not as instruction.

History

Pneumothorax was once deliberately induced as a treatment for pulmonary tuberculosis (artificial pneumothorax) in the early twentieth century before effective drug therapy. Modern understanding reframed it as a pathological accumulation of pleural air, and successive society guidelines codified its classification and a graded approach to assessment, with thoracic ultrasound and randomised trials more recently refining how it is evaluated.

Debates

How aggressively should uncomplicated primary spontaneous pneumothorax be treated?

Long-standing practice favoured intervention to re-expand the lung, but randomised evidence suggesting that conservative observation can be non-inferior for selected primary spontaneous pneumothoraces has reopened debate over when intervention is necessary.

Key figures

• Andrew MacDuff
• Simon G. A. Brown
• David Feller-Kopman
• Richard W. Light

Seminal works

• macduff-2010
• brown-2020

Frequently asked questions

What is the difference between primary and secondary spontaneous pneumothorax?

A primary spontaneous pneumothorax occurs without clinically apparent underlying lung disease, typically from rupture of small subpleural blebs, whereas a secondary spontaneous pneumothorax complicates established lung disease such as chronic obstructive pulmonary disease and tends to be more serious.

Why is a tension pneumothorax dangerous?

In a tension pneumothorax a one-way valve lets pleural air accumulate under positive pressure, which can shift the mediastinum and impair venous return to the heart, reducing cardiac output; it is regarded as a physiological emergency.