Which term describes air or gas in the pleural cavity?

• A. Hydrothorax
• B. Pneumothorax
• C. Pleural effusion
• D. Hemothorax

Answer: (B)

Air in the pleural cavity is called pneumothorax. The pleural space normally holds a small amount of lubricating fluid and maintains a negative pressure that keeps the lung expanded. When air enters this space—whether from a chest injury, rupture of an emphysematous bleb, or other causes—the negative pressure is disrupted and the lung can partially or completely collapse. This distinguishes it from hydrothorax (fluid in the pleural space, typically serous fluid), pleural effusion (a general term for fluid accumulation in the pleural space), and hemothorax (blood in the pleural space).