What is the Pleural Cavity and Why is it Important?

Anatomy and Structure of the Pleural Space

diagram showing the pleural cavity in the chest
What is the pleural cavity?. A.D.A.M. Medical Encyclopedia

Definition: Pleural Cavity

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 a thin fluid known as pleural fluid, which provides lubrication as the lungs expand and contract during respiration. The pleural space usually contains 15 to 20cc (or three to four teaspoons) of fluid.

Anatomy and Structure

The pleural cavity (or pleural space) is the area present between 2 pleural membranes.

These are the parietal (costal) pleura which are attached to the chest wall, and the visceral (pulmonary) pleura which are attached to the lungs. Within the pleural space is a small amount of serous fluid which is secreted by the pleura.


The pleural cavity serves to cushion the expansion and contraction of the lungs via a small amount of fluid which lubricates the pleura; decreasing friction so the lungs can expand and deflate smoothly. This is analogous to oil in a car which lubricates pistons in the engine.

The pleural cavity also serves as a vacuum, with pressure in this region (intrapleural pressure) being less than the pressure within the lungs (intrapulmonary pressure.)

Conditions Involving the Pleural Cavity

The presence of an excess of fluid, or of air or gas in the pleural cavity can interfere with its function in respiration.  Some conditions affecting the pleural space may include:

  • Pleural effusion - A pleural effusion refers to a build-up of fluid in the pleural cavity. When too much fluid accumulates in this space it can interfere with the expansion of the lungs with inspiration. There are many causes, with the most common being viral infections and congestive heart failure.
  • Malignant pleural effusion - In a malignant pleural effusion, fluid containing cancer cells accumulates in the pleural space. This complication occurs in roughly 30 percent of people with lung cancer, and by itself classifies the disease as stage 4 (metastatic.)
  • Pneumothorax - A pneumothorax refers to the presence of air in the pleural space. This build up of air can compress the nearby lungs. In the case of a tension pneumothorax, pressure accumulates due to air in the pleural space which seriously decreases the ability of the lungs to expand.
  • Hemothorax - With a hemothorax, blood accumulates in the pleural space.  The most common cause of this is chest trauma.
  • Mesothelioma - Mesothelioma is a cancer involving the pleural membranes, and is most commonly caused by exposure to asbestos.

Diagnosis and Procedures

If an excess amount of fluid is formed in the pleural cavity, a pleural effusion may develop. There are many causes of pleural effusions, ranging from heart failure to lung diseases to lung cancer. In order to diagnose a pleural effusion, your doctor may recommend a thoracentesis, a procedure in which a needle is placed into the cavity to remove pleural fluid. The pleural fluid is then analyzed under a microscope to look for the cause.

When air or fluid remain in the pleural space (of if the amount of fluid or air is large) a chest tube is often placed to drain the fluid or decompress the lungs. If symptoms recur—say, if fluid continues to accumulate or if air persists, a procedure called pleurodesis may be done. With this procedure, a substance is introduced into the pleural space which causes inflammation. This, in turn, causes the two layer of pleura to stick together, in essence obliterating the pleural space so air or fluid can no longer accumulate. If symptoms still persist, surgeons may consider removing the pleura and pleural space altogether, in a procedure known as pleurectomy.

Also Known As: pleural space

Examples: Ron was told he had an excess amount of fluid in his pleural cavity (a pleural effusion), and his doctor recommended doing a test to determine the cause.


U.S. National Library of Medicine. MedlinePlus. Pleural Disorders. Updated 05/11/16. https://medlineplus.gov/pleuraldisorders.html

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