What is defined as purulent pleural exudates resulting from a bacterial or mycotic infection?

Empyema is characterized by the presence of purulent pleural exudates, which are accumulations of pus in the pleural cavity, typically resulting from infections such as bacterial or fungal infections. This condition can occur when a pneumonia progresses to involve the pleural space or from direct infection of the pleura. The presence of purulent material indicates a significant immune response to the infection, including cellular debris, bacteria, and elevated white blood cell counts, which are key features of an empyema.

On the other hand, pneumothorax refers to the presence of air in the pleural space, which can lead to lung collapse but does not involve infection or pus accumulation. Pneumonia itself is an infection of the lung tissue and does not specifically refer to pleural involvement or the presence of pus. Pleural effusion is a broader term that describes any fluid accumulation in the pleural space, which can be caused by various conditions, including but not limited to infections, and does not specifically indicate that the fluid is purulent. Therefore, empyema specifically denotes the complication of pleural infection characterized by purulent effusions, making it the correct answer.