The pleural surface left demonstrates thick yellow-tan purulent exudate and the pleural cavity is filled with purulent exudate. This is an empyema. Pneumonia may be complicated by a pleuritis. Initially, there may just be an effusion into the pleural space. There may also be a fibrinous pleuritis. However, bacterial infections of lung can spread to the pleura to produce a purulent pleuritis. A collection of pus in the pleural space is known as empyema.