Pleural Cavity: Anatomy, Effusion Causes, Treatment

Buildup of fluid or air in the pleural space seriously impairs breathing

The pleural cavity is the space that lies between the pleura, the two thin membranes that line and surround the lungs. The pleural cavity contains a small amount of liquid known as pleural fluid, which provides lubrication as the lungs expand and contract during respiration. When increased fluid occupies this space, it is referred to as a pleural effusion and can severely restrict breathing depending on the size. Other disorders may also affect the pleural space such as a pneumothorax (build-up of air), a hemothorax (build-up of blood), and more.

Digital illustration of lung cancer
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Learn about the anatomy and function of the pleural cavity, as well as medical conditions that can affect this region of the body.

Anatomy of the Pleural Cavity

The pleural cavity is located between the parietal pleura (outer layer), that is attached to the chest wall and the visceral pleura (inner layer) that is attached to the lungs. Within the pleural space is between 15 and 20 ccs of fluid (roughly three to four teaspoons) secreted by cells in the pleura. (In contrast, with a pleural effusion this space may expand to contain several liters of fluid, fluid which can then work to compress the underlying lungs.)

Function of the Pleural Cavity

The pleural cavity’s function is to cushion the expansion and contraction of the lungs while ensuring it does so smoothly with the aid of the lubricating fluid.

Disorders Involving the Pleural Cavity

The presence of excess fluid, air, or gas in the pleural cavity can interfere with our ability to breathe and sometimes constitutes a medical emergency. A number of medical conditions can involve the pleural space.

Pleural Effusion

A pleural effusion is the buildup of excess fluid in the pleural cavity. This differs from pulmonary edema, which is when fluid builds up inside the lungs.

Pleural effusion can be serious depending on how much fluid accumulates. When it's only a small amount, a person may not experience any symptoms and the effusion may only be noted when an imaging test such as a chest X-ray or CT scan is done. In contrast, sometimes several liters of fluid accumulates in the pleural space causing severe shortness of breath, as the fluid in this space interferes with the normal expansion of the lungs required for inspiration.

Pleural effusion can have a number of underlying causes. Some of the main causes of a pleural effusion include:

  • Congestive heart failure: With congestive heart failure (CHF) a pleural effusion may develop due to increased capillary pressure in the lungs.
  • Infections: Pleural effusions may occur with a number of viral as well as bacterial infections.
  • Inflammation
  • Tumors: Tumors can cause a pleural effusion in a number of ways.
  • Cirrhosis of the liver: Hepatic hydrothorax is used to describe a pleural infusion caused by liver cirrhosis. It results from the movement of excess ascites fluids from the abdominal cavity to the pleural cavity.

People with pleural effusion may not have symptoms. When they do appear, symptoms of pleural effusion can include:

  • Chest pain
  • Shortness of breath (dyspnea)
  • A dry cough
  • Trouble breathing while lying down (orthopnea)

Malignant Pleural Effusion

A malignant pleural effusion is the initial sign of disease in 8% to 15% patients with lung cancer, while it develops during lung cancer progression in 40% to 50%.

However among patients presenting with a malignant pleural effusion, nearly 30% are due to lung cancer.


A hemothorax is the accumulation of blood in the pleural space, most often due to chest trauma or chest surgery.


A chylothorax refers to the accumulation of chyle (lymph fluid) in the pleural cavity and occurs when there is injury to the thoracic duct in the chest such as with trauma or chest surgery. A cyclothorax can also occur as a result of certain cancers such as lymphoma, or infections such as tuberculosis.


A pneumothorax (a collapsed lung) refers to the build-up of air in the pleural space. When a significant amount of air accumulates, it can compress the lungs and impede the ability of the lungs to expand. If a pneumothorax occurs, it can be a gradual process or, instead, a rapid process which compresses the lung beneath the lining (a tension pneumothorax).


Mesothelioma is a cancer of the pleural membranes most commonly associated with asbestos exposure.


A pleural effusion is often suspected when looking at a chest X-ray or chest CT scan, but further tests are needed to determine the components of the fluid and make a diagnosis. A thoracentesis is a procedure in which a long thin needle is inserted through the chest wall and into the pleural cavity to obtain a sample of fluid.The fluid can then be sent to pathology for further studies, such as chemistries, culture, and microscopic analysis for the presence of cancer cells.

A pleural effusion is typically diagnosed with thoracentesis. If fluid or air remains in the pleural space, a chest tube or needle thoracentesis, respectively, may be used decompress the lungs.


The treatment of pleural effusion and other disorders of the pleural space depends on the specific disorder, the severity, and the underlying causes or medical conditions.

With mesothelioma, if the tumor is operable a surgery may be done to remove the pleural membranes and underlying lung tissue.

Mild pleural effusions may resolve on their own. Thoracentesis is often the first step with larger effusions, thought fluid often reaccumulates (especially with malignant pleural effusions). If this happens, there are several options. A procedure called pleurodesis involves injecting an irritant (such as talc) between the pleural membranes to scar down the membranes and eliminate the pleural space. With malignant pleural effusions, a silicone catheter is often placed into the pleural cavity so that the fluid can be drained at home when it reaccumulates. In some cases, a pleurectomy (removal of the pleura) is needed.

With a pneumothorax, a chest tube is often placed to continuously remove the air until the air leak resolves on its own.

A Word From Verywell

The pleural cavity is a region of the body that is often taken for granted unless affected by the build up of fluid or air. Fortunately, prompt recognition can often lead to treatments that resolve or at least control these conditions.

3 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Charalampidis C, Youroukou A, Lazaridis G, et al. Pleura space anatomy. J Thorac Dis. 2015;7(Suppl 1):S27-32. doi: 10.3978/j.issn.2072-1439.2015.01.48

  2. Jany B, Welte T. Pleural Effusion in Adults-Etiology, Diagnosis, and Treatment. Dtsch Arztebl Int. 2019;116(21):377-386. doi:10.3238/arztebl.2019.0377

  3. Aydin Y, Turkyilmaz A, Intepe YS, Eroglu A. Malignant pleural effusions: appropriate treatment approaches. Eurasian J Med. 2009 Dec;41(3):186-93

Additional Reading
  • U.S. National Library of Medicine. Medline Plus. Pleural Disorders. Updated 02/07/19.

By Lynne Eldridge, MD
 Lynne Eldrige, MD, is a lung cancer physician, patient advocate, and award-winning author of "Avoiding Cancer One Day at a Time."