The Anatomy of the Pleura

The pleura is a vital part of the respiratory tract whose role it is to cushion the lungs and reduce any friction which may develop between the lungs, rib cage, and chest cavity. The pleura consists of a two-layered membrane that covers each lung. The layers are separated by a small amount of viscous lubricant known as pleural fluid.

There are a number of medical conditions that can affect the pleura, including pleural effusions, a collapsed lung, and cancer. When excess fluid accumulates between the pleural membranes, various procedures may be used to either drain the fluid or eliminate the space between the membranes.

There are two pleurae, one for each lung, and each pleura is a single membrane that folds back on itself to form two layers. The space between the membranes (called the pleural cavity) is filled with a thin, lubricating liquid (called pleural fluid).

The pleura is comprised 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 of the lungs (called the hilum).
• The parietal pleura is the outer membrane that lines the inner chest wall and diaphragm (the muscle separating the chest and abdominal cavities).

The visceral and parietal pleura join at the hilum, which also serves as the point of entry for the bronchus, blood vessels, and nerves.

The pleural cavity, also known as the intrapleural space, contains pleural fluid secreted by the mesothelial cells. The fluid allows the layers to glide over each other as the lungs inflate and deflate during respiration.

The structure of the pleura is essential to respiration, providing the lungs with the lubrication and cushioning needed to inhale and exhale. The intrapleural space contains roughly 4 cubic centimeters (ccs) to 5 ccs of pleural fluid which reduces friction whenever the lungs expand or contract.

The pleura fluid itself has a slightly adhesive quality that helps draw the lungs outward during inhalation rather than slipping round in the chest cavity. Pleural fluid also creates surface tension that helps maintain the position of the lungs against the chest wall.

The pleurae also serve as a division between other organs in the body, preventing them from interfering with lung function and vice versa.

There are a number of conditions that can cause injury to the pleura or undermine its function. Any injury of the membranes or overload of pleural fluid can affect how you breathe and lead to adverse respiratory symptoms.

There are several conditions known to affect the pleura or pleural function:

Pleurisy is an inflammation of the pleural membranes. It is most commonly caused by a viral infection but may also be the result of a bacterial infection or an autoimmune disease like rheumatoid arthritis or lupus.

Pleuritic inflammation causes the membrane surfaces to become rough and sticky. Rather than sliding over each other, the membranes will stick together, triggering sharp, stabbing pain whenever you breathe, sneeze, or cough. The pain can get worse when inhaling cold air or taking a deep breath. It can also worsen if you move or shift your body in different positions. Fever, chills, and loss of appetite may also accompany.

The treatment of pleurisy is focused on resolving the underlying cause. Antibiotics or antiviral drugs may be used to treat lung infections, while autoimmune diseases may require everything from nonsteroidal anti-inflammatory drugs (NSAIDs) to immunosuppressant drugs to temper the autoimmune inflammation.

A pleural effusion is the accumulation of excess fluid in the pleural space. When this happens, breathing can be impaired, sometimes significantly.

Congestive heart failure is the most common cause of a pleural effusion, but there is a multitude of other causes, including lung trauma or lung cancer (in which effusion is experienced in roughly half of all cases).

A pleural effusion can be very small (detectable only by a chest X-ray or CT scan) or be large and contain several pints of fluid. Common symptoms include chest pain, dry cough, shortness of breath, difficulty taking deep breaths, and persistent hiccups.

Pleural effusions can be treated in different ways, depending on the cause and severity of symptoms:

• Thoracentesis involves the extracting of fluid from the pleural cavity with a needle and syringe. The procedure is often guided by ultrasound to ensure correct needle placement.
• Tube thoracostomy, also known as a chest tube, may be used if there is an excessive build-up of fluid. This involves the insertion of a tube through the chest wall and into the pleural cavity. The tube is then attached to a suctioning device so that the fluid can be extracted.

A malignant pleural effusion refers to an effusion that contains cancer cells. It can be caused by a number of different cancers but is most commonly associated with lung cancer or breast cancer that has metastasized (spread) to the lungs.

Because pleural effusions tend to recur whenever cancer is involved, other treatments besides drainage may be needed.

One such procedure, called pleurodesis, involves the introduction of an irritating substance, such as talc, into the pleural cavity. The ensuing inflammation causes the layers to stick together, pressing out excess fluid. Depending on the stage of the malignancy and risk of effusion recurrence, the procedure may aim to temporarily or permanently fuse the tissue layers.

Pleural mesothelioma is a cancer of the pleura and is most commonly caused by occupational exposure to asbestos. Symptoms include pain in the shoulder, chest or lower back, shortness of breath, trouble swallowing, and swelling of the face and arms.

In people with mesothelioma, a surgical procedure called a pleurectomy ​may be recommended to remove a section of pleura (or an entire pleura) to prevent the buildup of fluid. It also allows the surgeon to remove any tumors that have developed inside the chest. A pleurectomy may also be considered for people who have recurrent pleural effusion.

Surgery combined with chemotherapy and/or radiation therapy may be used to remove the malignant tissue, relieve pleuritic symptoms, and control pleural effusions.

Pneumothorax is a condition in which air collects in the pleural cavity and is often described as a collapsed lung. It may be caused by any number of things, including chest trauma, chest surgery, and COPD. Along with shortness of breath, people may experience crepitus, an abnormal crackling sound from just under the skin of the neck and chest.

Spontaneous pneumothorax is a term used to describe when a lung collapses for no apparent reason. Tall, thin adolescent males are at greatest risk, although females can also be affected. Risk factors include smoking, connective tissue disorders, and activities such as scuba diving and flying in which atmospheric pressure changes rapidly.

In severe cases, such as the collapse of a lung due to emphysema, a surgical lobectomy may be needed to remove the diseased portion of a lung.

Hemothorax refers to the condition in which the pleural cavity becomes filled with blood. It most often occurs following a trauma injury or chest surgery; rarely, a hemothorax can happen spontaneously due to a vascular rupture.

The main symptom of hemothorax is pain or feeling of heaviness in the chest. Other symptoms include a very rapid heartbeat, trouble breathing, cold sweats, pale skin, and a fever.

Due to the viscosity of blood, hemothorax is more commonly treated with tube thoracostomy rather than thoracentesis. If the accumulation of blood is extreme, a surgery known as a thoracotomy may be performed to drain the pooled blood using an open incision between the chest ribs.