A parapneumonic effusion occurs when patients with pneumonia experience fluid building up in the pleural space. This is the space between the membrane that covers the lungs and the membrane that lines the chest cavity. Parapneumonic effusion can result from any type of pneumonia, and affects around 40 percent of all patients with bacterial pneumonia. Most often, the condition can be successfully treated using antibiotics. In more severe cases, a drainage tube is inserted between two of the ribs into the pleural space.
Parapneumonic effusion represents a special type of pleural effusion. The tissues that line the chest cavity and cover the lungs are known as the visceral pleura and parietal pleura. Normally, as the lungs expand and deflate during respiration, the pleurae slide past one another. They are helped by a small amount of lubricating pleural fluid between the two layers.
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A pleural effusion develops when an excess of fluid leaks into the pleural space. This can result from lung injury and inflammation, which is seen in pneumonia. It can also arise following increased pressure in blood vessels, which sometimes occurs in heart failure.
Parapneumonic effusions may be described as complicated or uncomplicated. Uncomplicated effusions are the result of inflammation seen in pneumonia. The fluid in the pleural space mostly consists of white blood cells, and typically the effusion resolves with antibiotics.
Complicated effusions arise when bacteria enter the pleural space. The immune system may remove the bacteria fairly quickly, but a collection of fluid may remain and require drainage. Sometimes pus collects inside the pleural space, and this type of parapneumonic effusion is known as empyema thoracis.
Empyema thoracis is diagnosed using a test known as thoracentesis. Fluid is drawn from the pleural space using a needle and thick pus indicates that the patient has empyema. This is the most serious form of parapneumonic effusion. The risk of developing it is greater in children and elderly people, and patients whose pneumonia has required a stay in hospital. Empyema thoracis is also more common in people with existing conditions such as diabetes, alcoholism and the lung disease known as bronchiectasis.
Most patients recover from parapneumonic effusion but in around ten percent the condition can be fatal. It is important to treat the condition as early as possible with antibiotic drugs and drainage of the pleural space. In a few cases, a surgical procedure is necessary to remove pus and scar tissue.