A parapneumonic effusion is a type of pleural effusion that arises as a result of a pneumonia, lung abscess, or bronchiectasis. There are three types of parapneumonic effusions: uncomplicated effusions, complicated effusions, and empyema. Uncomplicated effusions generally respond well to appropriate antibiotic treatment. The criteria for a complicated parapneumonic effusion include Gram stain–positive or culture-positive pleural fluid, pleural fluid pH
Hubert van den Bergh, Georges Wagnières