A pneumothorax involves air accumulating in which space?

• A. Lung parenchyma
• B. Pleural cavity
• C. Alveolar space
• D. Pericardial sac

Answer: (B)

A pneumothorax is when air gets into the pleural cavity, the space between the lung and the chest wall. That space normally contains a tiny amount of fluid and a negative pressure that helps keep the lung expanded. When air enters here, the negative pressure is lost, the lung cannot stay fully inflated, and it may collapse. This distinguishes it from air inside the lung tissue (lung parenchyma) or inside the alveolar spaces, and from air in the pericardial sac around the heart.