A hemothorax is best defined as which of the following?

• A. Bleeding into the pleural space
• B. Air in the pleural space
• C. Collapse of the lung due to fluid
• D. Pneumonia affecting the pleural space

Answer: (A)

Bleeding into the pleural space describes a hemothorax. The pleural space is the thin gap between the lung surface and the chest wall; normally it contains just a small amount of lubricating fluid. When blood collects there, it can compress the lung and cause shortness of breath. Hemothorax usually results from chest trauma, rib fractures, surgical bleeding, or ruptured vessels, and is often seen with signs like decreased breath sounds and dullness to percussion on the affected side. Imaging may show a fluid level with blood-density material layering in the chest.

The other descriptions refer to different problems: air in the pleural space is a pneumothorax; a lung collapse due to fluid isn’t the standard way we define a hemothorax; and pneumonia affecting the pleural space implies a parapneumonic effusion or empyema, not simply blood in the space.