page_title: Pleural cavity
section_title: Pleural effusion
hierarchical_section_title: Pleural cavity / Clinical significance / Pleural effusion
context_page_description: The pleural cavity also known as the pleural space, is the thin fluid-filled space between the two pulmonary pleurae of each lung. A pleura is a serous membrane which folds back onto itself to form a two-layered membranous pleural sac. The outer pleura is attached to the chest wall, but is separated from it by the endothoracic fascia. The inner pleura covers the lungs and adjoining structures, including blood vessels, bronchi and nerves. The pleural cavity can be viewed as a potential space because the two pleurae adhere to each other under all normal conditions.
context_section_description: A pathologic collection of pleural fluid is called a pleural effusion. Mechanisms:
  Lymphatic obstruction
  Increased capillary permeability
  Decreased plasma colloid osmotic pressure
  Increased capillary venous pressure
  Increased negative intrapleural pressure
  Pleural effusions are classified as exudative (high protein) or transudative (low protein).  Exudative pleural effusions are generally caused by infections such as pneumonia (parapneumonic pleural effusion), malignancy, granulomatous disease such as tuberculosis or coccidioidomycosis, collagen vascular diseases, and other inflammatory states.  Transudative pleural effusions occur in congestive heart failure (CHF), cirrhosis or nephrotic syndrome.
  Localized pleural fluid effusion noted during pulmonary embolism (PE) results probably from increased capillary permeability due to cytokine or inflammatory mediator release from the platelet-rich thrombi.
caption: A pleural effusion can form when fluid builds up in the pleural space.