An accumulation of fluid between the layers of the pleura, the membrane that separates the lungs from the chest wall
A pleural effusion occurs when fluid accumulates between the layers of the pleura, the two-layered membrane separating the lungs from the chest wall. As fluid accumulates, the lung underneath becomes compressed, gradually causing shortness of breath. In some cases, the amount of fluid accumulated may be as much as 2–3 litres (4–6 pints).
In most cases of pleural effusion, the pleura itself is inflamed and produces fluid (see Pleurisy). The inflammation may be due to a lung infection, such as pneumonia or tuberculosis, or to other disorders that affect the lung, such as lung cancer (see Primary lung cancer) or cancer that has spread to the pleura from elsewhere in the body, for example from the breast, ovary, or bowel. Less often, the cause may be an autoimmune disorder, such as systemic lupus erythematosus, in which the immune system attacks the body’s own tissues.
In some cases, the pleura itself is not the cause of the effusion. Instead, fluid leaks into the space between the pleural layers as a result of a serious underlying disorder, such as heart failure (see Acute heart failure and Chronic heart failure), or kidney disease. In these cases, a pleural effusion is often associated with a build-up of fluid elsewhere in the body, such as in the ankles or abdomen.
A pleural effusion that produces little fluid may not cause symptoms. In severe cases, a large amount of fluid between the pleural layers compresses the lungs and may result in shortness of breath.
Your doctor may be able to detect a pleural effusion while examining your chest. You may also have a chest X-ray to confirm the diagnosis and to assess the severity of the effusion. In order to identify the underlying cause, your doctor may take a sample of fluid by inserting a needle through the chest wall under local anaesthesia. A sample of the pleura may also be removed. The sample is examined under a microscope to look for evidence of infection or cancer. A sample of blood may be taken for testing to exclude other problems, such as kidney disorders.
Shortness of breath due to a severe pleural effusion may be relieved by removing some of the fluid through a tube inserted into the chest under local anaesthesia. Your doctor may prescribe antibiotics if a bacterial infection is the cause of the effusion. Diuretic drugs may be given to reduce the volume of fluid in the body. An effusion that is associated with lung cancer may be treated by chemotherapy, in which anticancer drugs are injected between the pleural layers, or occasionally by radiotherapy. Usually, the excess fluid slowly disappears once the underlying cause has been treated.
In some people, particularly those who have lung cancer, pleural effusion may recur. If the effusion does recur, a chemical can be injected into the chest cavity to make the two layers of the pleura stick together.
From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.