Pneumothorax is most commonly caused by which mechanism?

• A. Bacterial infection
• B. Asthma
• C. Lung surface ruptures causing air leak due to over pressurization or chest trauma
• D. Heart failure

Answer: (C)

Pneumothorax happens when air enters the pleural space after the lung surface ruptures. The most common mechanism is rupture of the lung surface—often a small bleb or alveolar rupture—leading to an ongoing air leak into the pleural space. This rupture is typically driven by over-pressurization of the lung (barotrauma) or by chest trauma, such as blunt impact or penetrating injury. The continuous air leak causes the lung to collapse partially or fully, resulting in shortness of breath and chest pain.

Bacterial infection can cause pneumonia or pleural infection but not an air leak into the pleural space. Asthma in itself isn’t the direct mechanism, though severe overinflation can contribute to barotrauma in some cases. Heart failure leads to fluid buildup in the lungs or pleural space (effusions) rather than air in the pleural space.