Pleural cavity

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Pleural cavity
2313 The Lung Pleurea.jpg
The pleural cavity is the potential space between the pleurae of the pleural sac that surrounds each lung.
Details
Precursor intraembryonic coelom
Identifiers
Latin cavum pleurae, cavum pleurale, cavitas pleuralis
MeSH D035422
TA98 A07.1.01.001
TA2 3316
TH H3.05.03.0.00013
FMA 9740
Anatomical terminology

The pleural cavity, pleural space, or interpleural space is the potential space between the pleurae of the pleural sac that surrounds each lung. A small amount of serous pleural fluid is maintained in the pleural cavity to enable lubrication between the membranes, and also to create a pressure gradient. [1]

Contents

The serous membrane that covers the surface of the lung is the visceral pleura and is separated from the outer membrane the parietal pleura by just the film of pleural fluid in the pleural cavity. The visceral pleura follows the fissures of the lung and the root of the lung structures. The parietal pleura is attached to the mediastinum, the upper surface of the diaphragm, and to the inside of the ribcage. [1]

Structure

In humans, the left and right lungs are completely separated by the mediastinum, and there is no communication between their pleural cavities. Therefore, in cases of a unilateral pneumothorax, the contralateral lung will remain functioning normally unless there is a tension pneumothorax, which may shift the mediastinum and the trachea, kink the great vessels and eventually collapse the contralateral cardiopulmonary circulation.

The visceral pleura receives its blood supply from the parenchymal capillaries of the underlying lung, which have input from both the pulmonary and the bronchial circulation. The parietal pleura receives its blood supply from whatever structures underlying it, which can be branched from the aorta (intercostal, superior phrenic and inferior phrenic arteries), the internal thoracic (pericardiacophrenic, anterior intercostal and musculophrenic branches), or their anastomosis.

The visceral pleurae are innervated by splanchnic nerves from the pulmonary plexus, which also innervates the lungs and bronchi. The parietal pleurae however, like their blood supplies, receive nerve supplies from different sources. The costal pleurae (including the portion that bulges above the thoracic inlet) and the periphery of the diaphragmatic pleurae are innervated by the intercostal nerves from the enclosing rib cage, which branches off from the T1-T12 thoracic spinal cord. The mediastinal pleurae and central portions of the diaphragmatic pleurae are innervated by the phrenic nerves. which branches off the C3-C5 cervcial cord. Only the parietal pleurae contain somatosensory nerves and are capable of perceiving pain.

Development

During the third week of embryogenesis, each lateral mesoderm splits into two layers. The dorsal layer joins the overlying somites and ectoderm to form the somatopleure; and the ventral layer joins the underlying endoderm to form the splanchnopleure. [2] The dehiscence of these two layers creates a fluid-filled cavity on each side, and with the ventral infolding and the subsequent midline fusion of the trilaminar disc, forms a pair of intraembryonic coeloms anterolaterally around the gut tube during the fourth week, with the splanchnopleure on the inner cavity wall and the somatopleure on the outer cavity wall.

The cranial end of the intraembryonic coeloms fuse early to form a single cavity, which rotates invertedly and apparently descends in front of the thorax, and is later encroached by the growing primordial heart as the pericardial cavity. The caudal portions of the coeloms fuse later below the umbilical vein to become the larger peritoneal cavity, separated from the pericardial cavity by the transverse septum. The two cavities communicate via a slim pair of remnant coeloms adjacent to the upper foregut called the pericardioperitoneal canal. During the fifth week, the developing lung buds begin to invaginate into these canals, creating a pair of enlarging cavities that encroach into the surrounding somites and further displace the transverse septum caudally — namely the pleural cavities. The mesothelia pushed out by the developing lungs arise from the splanchnopleure, and become the visceral pleurae; while the other mesothelial surfaces of the pleural cavities arise from the somatopleure, and become the parietal pleurae.

The tissue separating the newly formed pleural cavities from the pericardial cavity are known as the pericardiopleural membranes, which later become the side walls of the fibrous pericardium. The transverse septum and the displaced somites fuse to form the pleuroperitoneal membranes, which separates the pleural cavities from the peritoneal cavity and later becomes the diaphragm.

Function

The pleural cavity, with its associated pleurae, aids optimal functioning of the lungs during breathing. The pleural cavity also contains pleural fluid, which acts as a lubricant and allows the pleurae to slide effortlessly against each other during respiratory movements. [3] Surface tension of the pleural fluid also leads to close apposition of the lung surfaces with the chest wall. This relationship allows for greater inflation of the alveoli during breathing. The pleural cavity transmits movements of the ribs muscles to the lungs, particularly during heavy breathing. During inhalation the external intercostals contract, as does the diaphragm. This causes the expansion of the chest wall, that increases the volume of the lungs. A negative pressure is thus created and inhalation occurs.

Pleural fluid

Pleural fluid is a serous fluid produced by the serous membrane covering normal pleurae. Most fluid is produced by the exudation in parietal circulation (intercostal arteries) via bulk flow and reabsorbed by the lymphatic system. [4] Thus, pleural fluid is produced and reabsorbed continuously. The composition and volume is regulated by mesothelial cells in the pleura. [5] In a normal 70 kg human, a few milliliters of pleural fluid is always present within the intrapleural space. [6] Larger quantities of fluid can accumulate in the pleural space only when the rate of production exceeds the rate of reabsorption. Normally, the rate of reabsorption increases as a physiological response to accumulating fluid, with the reabsorption rate increasing up to 40 times the normal rate before significant amounts of fluid accumulate within the pleural space. Thus, a profound increase in the production of pleural fluid—or some blocking of the reabsorbing lymphatic system—is required for fluid to accumulate in the pleural space.

Pleural fluid circulation

The hydrostatic equilibrium model, viscous flow model and capillary equilibrium model are the three hypothesised models of circulation of pleural fluid. [7]

According to the viscous flow model, the intra pleural pressure gradient drives a downward viscous flow of pleural fluid along the flat surfaces of ribs.The capillary equilibrium model states that the high negative apical pleural pressure leads to a basal-to-apical gradient at the mediastinal pleural surface, leading to a fluid flow directed up towards the apex (helped by the beating heart and ventilation in lungs).Thus the recirculation of fluid occurs. Finally there's a traverse flow from margins to flat portion of ribs completes the fluid circulation. [8] [9]

Absorption occurs into lymphatic vessels at the level of the diaphragmatic pleura. [10]

Clinical significance

Pleural effusion

A pleural effusion can form when fluid builds up in the pleural cavity (labelled as pleural space). Diagram showing a build up of fluid in the lining of the lungs (pleural effusion) CRUK 054.svg
A pleural effusion can form when fluid builds up in the pleural cavity (labelled as pleural space).

A pathologic collection of pleural fluid is called a pleural effusion. Mechanisms:

  1. Lymphatic obstruction
  2. Increased capillary permeability
  3. Decreased plasma colloid osmotic pressure
  4. Increased capillary venous pressure
  5. 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. [11]

Transudate [12] Exudative causes [12]
* Congestive heart failure (CHF) * Malignancy

Pleural fluid analysis

When accumulation of pleural fluid is noted, cytopathologic evaluation of the fluid, as well as clinical microscopy, microbiology, chemical studies, tumor markers, pH determination and other more esoteric tests are required as diagnostic tools for determining the causes of this abnormal accumulation. Even the gross appearance, color, clarity and odor can be useful tools in diagnosis. The presence of heart failure, infection or malignancy within the pleural cavity are the most common causes that can be identified using this approach. [13]

Gross appearance

  • Clear straw-colored: If transudative, no further analysis needed. If exudative, additional studies needed to determine cause (cytology, culture, biopsy).
  • Cloudy, purulent, turbid: Infection, empyema, pancreatitis, malignancy.
  • Pink to red/bloody: Traumatic tap, malignancy, pulmonary infarction, intestinal infarction, pancreatitis, trauma.
  • Green-white, turbid: Rheumatoid arthritis with pleural effusion.
  • Green-brown: Biliary disease, bowel perforation with ascites.
  • Milky-white or yellow and bloody: Chylous effusion.
  • Milky or green, metallic sheen: Pseudochylous effusion.
  • Viscous (hemorrhagic or clear): Mesothelioma.
  • Anchovy-paste (or 'chocolate sauce'): Ruptured amoebic liver abscess. [12]

Microscopic appearance

Microscopy may show resident cells (mesothelial cells, inflammatory cells) of either benign or malignant etiology. Evaluation by a cytopathologist is then performed and a morphologic diagnosis can be made. Neutrophils are numerous in pleural empyema. If lymphocytes predominate and mesothelial cells are rare, this is suggestive of tuberculosis. Mesothelial cells may also be decreased in cases of rheumatoid pleuritis or post-pleurodesis pleuritis. Eosinophils are often seen if a patient has recently undergone prior pleural fluid tap. Their significance is limited. [14]

If malignant cells are present, a pathologist may perform additional studies including immunohistochemistry to determine the etiology of the malignancy.

Chemical analysis

Chemistry studies may be performed including pH, pleural fluid:serum protein ratio, LDH ratio, specific gravity, cholesterol and bilirubin levels. These studies may help clarify the etiology of a pleural effusion (exudative vs transudative). Amylase may be elevated in pleural effusions related to gastric/esophageal perforations, pancreatitis or malignancy. Pleural effusions are classified as exudative (high protein) or transudative (low protein).

In spite of all the diagnostic tests available today, many pleural effusions remain idiopathic in origin. If severe symptoms persist, more invasive techniques may be required. In spite of the lack of knowledge of the cause of the effusion, treatment may be required to relieve the most common symptom, dyspnea, as this can be quite disabling. Thoracoscopy has become the mainstay of invasive procedures as closed pleural biopsy has fallen into disuse.

Disease

Diseases of the pleural cavity include:

See also

Related Research Articles

Abdominal cavity Body cavity in the abdominal area

The abdominal cavity is a large body cavity in humans and many other animals that contains many organs. It is a part of the abdominopelvic cavity. It is located below the thoracic cavity, and above the pelvic cavity. Its dome-shaped roof is the thoracic diaphragm, a thin sheet of muscle under the lungs, and its floor is the pelvic inlet, opening into the pelvis.

Body cavity

A body cavity is any space or compartment, or potential space, in an animal body. Cavities accommodate organs and other structures; cavities as potential spaces contain fluid.

Respiratory tract Organs involved in transmission of air to and from the point where gases diffuse into tissue

The respiratory tract is the subdivision of the respiratory system involved with the process of respiration in mammals. The respiratory tract is lined with respiratory epithelium as respiratory mucosa.

Mesothelium

The mesothelium is a membrane composed of simple squamous epithelial cells of mesodermal origin, which forms the lining of several body cavities: the pleura, peritoneum and pericardium.

Pleural effusion Accumulation of excess fluid in the pleural cavity

A pleural effusion is accumulation of excessive fluid in the pleural space, the potential space that surrounds each lung. Under normal conditions, pleural fluid is secreted by the parietal pleural capillaries at a rate of 0.6 millilitre per kilogram weight per hour, and is cleared by lymphatic absorption leaving behind only 5–15 millilitres of fluid, which helps to maintain a functional vacuum between the parietal and visceral pleurae. Excess fluid within the pleural space can impair inspiration by upsetting the functional vacuum and hydrostatically increasing the resistance against lung expansion, resulting in a fully or partially collapsed lung.

Atelectasis Collapse or closure of a lung resulting in reduced or absent gas exchange

Atelectasis is the collapse or closure of a lung resulting in reduced or absent gas exchange. It is usually unilateral, affecting part or all of one lung. It is a condition where the alveoli are deflated down to little or no volume, as distinct from pulmonary consolidation, in which they are filled with liquid. It is often called a collapsed lung, although that term may also refer to pneumothorax.

Serous membrane Smooth coating lining contents & inner walls of body cavities

In anatomy, serous membrane is a smooth tissue membrane of mesothelium lining the contents and inner walls of body cavities, which secrete serous fluid to allow lubricated sliding movements between opposing surfaces. The serous membrane that covers internal organs is called a visceral membrane; while the one that covers the cavity wall is called the parietal membrane. Between the two opposing serosal surfaces is often a potential space, mostly empty except for the small amount of serous fluid.

Hemothorax Blood accumulation in the pleural cavity

A hemothorax is an accumulation of blood within the pleural cavity. The symptoms of a hemothorax may include chest pain and difficulty breathing, while the clinical signs may include reduced breath sounds on the affected side and a rapid heart rate. Hemothoraces are usually caused by an injury, but they may occur spontaneously due to cancer invading the pleural cavity, as a result of a blood clotting disorder, as an unusual manifestation of endometriosis, in response to a collapsed lung, or rarely in association with other conditions.

Chylothorax Medical condition

A chylothorax is an abnormal accumulation of chyle, a type of lipid-rich lymph, in the space surrounding the lung. The lymphatics of the digestive system normally returns lipids absorbed from the small bowel via the thoracic duct, which ascends behind the esophagus to drain into the left brachiocephalic vein. If normal thoracic duct drainage is disrupted, either due to obstruction or rupture, chyle can leak and accumulate within the negative-pressured pleural space. In people on a normal diet, this fluid collection can sometimes be identified by its turbid, milky white appearance, since chyle contains emulsified triglycerides.

Thoracentesis Medical procedure

Thoracentesis, also known as thoracocentesis, pleural tap, needle thoracostomy, or needle decompression, is an invasive medical procedure to remove fluid or air from the pleural space for diagnostic or therapeutic purposes. A cannula, or hollow needle, is carefully introduced into the thorax, generally after administration of local anesthesia. The procedure was first performed by Morrill Wyman in 1850 and then described by Henry Ingersoll Bowditch in 1852.

Respiratory disease Disease of the respiratory system

Respiratory diseases, or lung diseases, are pathological conditions affecting the organs and tissues that make gas exchange difficult in air-breathing animals. They include conditions of the respiratory tract including the trachea, bronchi, bronchioles, alveoli, pleurae, pleural cavity, the nerves and muscles of respiration. Respiratory diseases range from mild and self-limiting, such as the common cold, influenza, and pharyngitis to life-threatening diseases such as bacterial pneumonia, pulmonary embolism, tuberculosis, acute asthma, lung cancer, and severe acute respiratory syndromes, such as COVID-19. Respiratory diseases can be classified in many different ways, including by the organ or tissue involved, by the type and pattern of associated signs and symptoms, or by the cause of the disease.

Pericardial effusion Medical condition

A pericardial effusion is an abnormal accumulation of fluid in the pericardial cavity. The pericardium is a two-part membrane surrounding the heart: the outer fibrous connective membrane and an inner two-layered serous membrane. The two layers of the serous membrane enclose the pericardial cavity between them. This pericardial space contains a small amount of pericardial fluid. The fluid is normally 15-50 mL in volume. The pericardium, specifically the pericardial fluid provides lubrication, maintains the anatomic position of the heart in the chest, and also serves as a barrier to protect the heart from infection and inflammation in adjacent tissues and organs.

Hemopneumothorax, or haemopneumothorax, is the condition of having air in the chest cavity (pneumothorax) and blood in the chest cavity (hemothorax). A hemothorax, pneumothorax, or the combination of both can occur due to an injury to the lung or chest.

Root of the lung

The root of the lung is a group of structures that emerge at the hilum of each lung, just above the middle of the mediastinal surface and behind the cardiac impression of the lung. It is nearer to the back than the front. The root of the lung is connected by the structures that form it to the heart and the trachea. The rib cage is separated from the lung by a two-layered membranous coating, the pleura. The hilum is the large triangular depression where the connection between the parietal pleura and the visceral pleura is made, and this marks the meeting point between the mediastinum and the pleural cavities.

Pleural disease occurs in the pleural space, which is the thin fluid-filled area in between the two pulmonary pleurae in the human body. There are several disorders and complications that can occur within the pleural area, and the surrounding tissues in the lung.

Tumor-like disorders of the lung pleura are a group of conditions that on initial radiological studies might be confused with malignant lesions. Radiologists must be aware of these conditions in order to avoid misdiagnosing patients. Examples of such lesions are: pleural plaques, thoracic splenosis, catamenial pneumothorax, pleural pseudotumor, diffuse pleural thickening, diffuse pulmonary lymphangiomatosis and Erdheim–Chester disease.

Asbestos-related diseases Medical condition

Asbestos-related diseases are disorders of the lung and pleura caused by the inhalation of asbestos fibres. Asbestos-related diseases include non-malignant disorders such as asbestosis, diffuse pleural thickening, pleural plaques, pleural effusion, rounded atelectasis and malignancies such as lung cancer and malignant mesothelioma.

Litten's sign, also known as the diaphragm phenomenon, is a paralyzed hemidiaphragm, the portion of the diaphragm in contact with the parietal pleura during respiration in the base of the pleural cavity.

Pulmonary pleurae Serous membrane that lines the wall of the thoracic cavity and the surface of the lung

The pulmonary pleurae are the two opposing layers of serous membrane overlying the lungs and the inside of the surrounding chest walls.

Ventilation-perfusion coupling

Ventilation-perfusion coupling is the relationship between ventilation and perfusion processes, which take place in the respiratory and cardiovascular systems. Ventilation is the movement of gas during breathing, and perfusion is the process of pulmonary blood circulation, which delivers oxygen to body tissues. Anatomically, the lung structure, alveolar organization, and alveolar capillaries contribute to the physiological mechanism of ventilation and perfusion. Ventilation-perfusion coupling maintains a constant ratio near 0.8 on average, while the regional variation exists within the lungs due to gravity. When the ratio gets above or below 0.8, it is considered abnormal ventilation-perfusion coupling, also known as a ventilation-perfusion mismatch. Lung diseases, cardiac shunts, and smoking can cause a ventilation-perfusion mismatch that results in significant symptoms and diseases, which can be treated through treatments like bronchodilators and oxygen therapy.

References

  1. 1 2 Saladin, Kenneth S. (2011). Human anatomy (3rd ed.). New York: McGraw-Hill. pp. 643–644. ISBN   9780071222075. OCLC   780984149.
  2. ↑ Larsen, William J. (2001). Human embryology (3. ed.). Philadelphia, Pa.: Churchill Livingstone. p.  138. ISBN   9780443065835. OCLC   902010725.
  3. ↑ Light 2007, p. 1.
  4. ↑ Miserocchi, G. (2009-12-01). "Mechanisms controlling the volume of pleural fluid and extravascular lung water". European Respiratory Review. 18 (114): 244–252. doi: 10.1183/09059180.00002709 . ISSN   0905-9180. PMID   20956149.
  5. ↑ Zocchi, L. (December 2002). "Physiology and pathophysiology of pleural fluid turnover". European Respiratory Journal. 20 (6): 1545–1558. doi: 10.1183/09031936.02.00062102 . ISSN   0903-1936. PMID   12503717.
  6. ↑ Widmaier, Eric P.; Raff, Hershel; Strang, Kevin T. (2006). Vander's human physiology : the mechanisms of body function (10th ed.). Boston, Massachusetts: McGraw-Hill. ISBN   978-0072827415.
  7. ↑ Casha, Aaron R.; Caruana-Gauci, Roberto; Manche, Alexander; Gauci, Marilyn; Chetcuti, Stanley; Bertolaccini, Luca; Scarci, Marco (April 2017). "Pleural pressure theory revisited: a role for capillary equilibrium". Journal of Thoracic Disease. 9 (4): 979–989. doi: 10.21037/jtd.2017.03.112 . ISSN   2072-1439. PMC   5418293 . PMID   28523153.
  8. ↑ Boron, Walter F.; Boulpaep, Emile L. (2015). Fisiologia medica (2). Elsevier Mosby. ISBN   978-85-352-6851-5. OCLC   949753083.
  9. ↑ Lai-Fook, Stephen J. (April 2004). "Pleural mechanics and fluid exchange". Physiological Reviews. 84 (2): 385–410. doi:10.1152/physrev.00026.2003. ISSN   0031-9333. PMID   15044678.
  10. ↑ Shintani, Yasushi; Funaki, Soichiro; Ose, Naoko; Kawamura, Tomohiro; Kanzaki, Ryu; Minami, Masato; Okumura, Meinoshin (June 2018). "Air leak pattern shown by digital chest drainage system predict prolonged air leakage after pulmonary resection for patients with lung cancer". Journal of Thoracic Disease. 10 (6): 3714–3721. doi: 10.21037/jtd.2018.05.150 . ISSN   2072-1439. PMC   6051872 . PMID   30069369.
  11. ↑ Porcel, J.M.; R.W. Light (July 2008). "Pleural effusions due to pulmonary embolism". Current Opinion in Pulmonary Medicine. 14 (4): 337–42. doi:10.1097/MCP.0b013e3282fcea3c. PMID   18520269. S2CID   44337698.
  12. 1 2 3 Galagan, Katherine A. (2006). Color Atlas of Body Fluids: an illustrated field guide based on proficiency testing. Northfield, Ill.: CAP Press. ISBN   9780930304911. OCLC   78070199.
  13. ↑ Shidham, Vinod B.; Atkinson, Barbara F. (2007). Cytopathologic diagnosis of serous fluids (1st ed.). Philadelphia, Pennsylvania: Saunders Elsevier. ISBN   978-1416001454. OCLC   1239350014.
  14. ↑ De Mais, Daniel. ASCP Quick Compendium of Clinical Pathology, 2nd. Ed. ASCP Press, Chicago, 2009.

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