Function and Disorders of the Pleura

The pleura is a vital part of the respiratory tract whose purpose it is to cushion the lungs and reduce any friction which may develop between the lungs, rib cage, and chest cavity. What is the structure of the pleura and what medical conditions affect this region of the boy?

The pleura specifically refers to the two membranes that cover the lungs. The space between the two membranes is called the pleural cavity which is filled with a thin, lubricating liquid called pleural fluid. The pleura is made up of two, distinct layers:

• The visceral pleura is the thin, slippery membrane that covers the surface of the lungs and dips into the areas separating the different lobes (called the hilum.)
• The parietal pleura is the outer membrane that lines the inner chest wall and diaphragm.

The visceral and parietal pleura join at the hilum of each lung, where the major bronchi, pulmonary arteries, and pulmonary veins enter the lung.

The two membranes that make up the pleura serve primarily to reduce friction when the lungs expand and contract during breathing. A small amount of fluid between these layers, roughly 4 to 5 cc of pleural fluid, helps to act as a cushion.

The pleura is not the only set of membranes lining body cavities. There is a membrane around the heart (pericardium) and a membrane lining the abdominal cavity (peritoneum) as well.

Under the influence of the lubricating fluid, the pleura membranes are able to glide atop each other, allowing the lungs to expand during inhalation and relax during exhalation. If the pleura becomes scarred, or if fluid builds up in the space between these membranes, it can restrict movement and interfere with breathing.

There are several conditions that can adversely affect the pleura. If inflammation is involved, the pain tends to be sharp and felt with each breath. Pain that worsens with a deep breath and often feels sharp is specifically referred to as "pleuritic" chest pain.

Among the conditions involving the pleura:

• Pleurisy is an inflammation of the pleural membranes during which the surfaces become rough and sticky. It is most commonly caused by viral infections but can be caused by bacteria and autoimmune diseases such as rheumatoid arthritis and lupus. The discomfort that accompanies pleurisy tends to worsen when going outdoors in cold weather.
• Pleural effusion in the accumulation of excess fluid in the pleural space. When this happens, breathing can be impaired. Congestive heart failure is the most common cause of a pleural effusion, but there are a multitude of potential causes. A pleural effusion can be very small, and only seen on imaging studies such as a chest x-ray or CT scan, or large, containing several pints of fluid.
• Malignant pleural effusion refers to an effusion caused by lung cancer, or other cancers such as breast cancer that have spread (metastasized) to the lungs from other parts of the body.
• Pleural mesothelioma is a cancer of the pleura, is most commonly caused by occupational exposure to asbestos.

Disorders of the pleura can sometimes be symptom-free and resolve on their own. Other require medical intervention. Treatment will depend largely on the underlying cause of the disorder. If the excessive accumulation of fluid, blood, or air is involved, a chest tube may be used to help remove it.

Smaller pleural effusions may go away on their own; larger ones will need to be drained. The first step is usually extracting the fluid with a needle guided through the skin of the chest and into the pleural cavity (thoracentesis). Often times, depending on the cause, a pleural effusion will recur, especially if it is related to cancer.

With recurrent pleural effusions there are a few options. First, a thoracentesis may be repeated. If the pleural effusion recurs, the next step will depend on the underlying cause and the condition of the person with the pleural effusion. In relatively healthy people, a procedure called pleurodesis is often done. This is a surgery in which an irritating substance, such as talc, is placed between the two layers of the pleura. The talc causes irritation and inflammation, eventually causing the two layers to adhere and become "glued" together, so that the pleural cavity no longer exists for fluid to accumulate.

With cancer, a pleural effusion is often a concern near the end of life. When this is the case, an indwelling catheter may be placed in the pleural cavity so that the effusion can be drained either continuously, or whenever it is causing significant shortness of breath.

If people with mesothelioma, a surgical procedure called a pleurectomy ​may be performed to remove a section of pleura or the whole pleura to prevent the buildup of fluid. It also allows the surgeon to remove any tumors that have developed inside the chest.