What is empyema?

Empyema refers specifically to the presence of pus in the pleural space, which is the area between the layers of tissue lining the lungs and the chest cavity. This condition typically results from an infection or inflammation that leads to the accumulation of purulent material as the body's immune response attempts to fight off infection. This pus is composed of bacteria, dead cells, and inflammatory substance, and its presence can lead to symptoms such as chest pain, fever, and difficulty breathing.

Understanding this, it becomes evident that while fluid buildup in the pleural space could occur in various conditions, it is the specific accumulation of pus that defines empyema. Other options may describe related pleural conditions, but none captures the distinct nature of empyema like the presence of pus does.