What pathology does empyema involve?

• A. Blood in alveoli.
• B. Fluid in pericardial space.
• C. Pus in pleural space.
• D. Air in pleural space.

Answer: (C)

Empyema is pus in the pleural space—the area between the lung and the chest wall. It happens when an infection, often from pneumonia or a nearby lung infection, spills into the pleural cavity and produces thick, purulent fluid that can become loculated. This distinguishes empyema from a simple pleural effusion, which is just fluid in that space without pus, and from other thoracic problems. The other scenarios describe different conditions: blood in the alveoli is alveolar hemorrhage, fluid in the pericardial space is a pericardial effusion, and air in the pleural space is a pneumothorax. So the pathology described by empyema is pus in the pleural space.