Pleura

The pleura is a serous membrane that lines the walls of the thoracic cavity and the surface of the lungs. This structure of mesodermal origin covers both lungs, the mediastinum, the thoracic surface of the diaphragm, and the inner part of the thoracic cage. The pleura is divided into a visceral pleura and parietal pleura. Between both layers, there is a well-lubricated potential space called the pleural cavity, which eases the respiratory movements of the lungs and helps avoid friction.

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Gross Anatomy

The pleura is a double-layered serous membrane that lines the walls of the thoracic cavity and the surface of the lungs. Thus, it extends virtually as far and wide as the thoracic cavity.

Boundaries: 

  • Superior: root of neck 2–3 cm above rib 1
  • Inferior: thoracic surface of the diaphragm
  • Medial: mediastinum
  • Lateral: inner surface of the rib cage and intercostal muscles
Boundaries and parts of the pleura within the thoracic cavity

Boundaries and parts of the pleura within the thoracic cavity

Image by Lecturio. License: CC BY-NC-SA 4.0

Each lung is enclosed in a serous pleural sac that consists of 2 continuous membranes of visceral and parietal pleura.

  • Parietal pleura:
    • Lines the inner surface of the thoracic cavity
    • Separated from the thoracic wall by the endothoracic fascia
    • Parts are classified according to the adjacent structures:
      • Costal pleura
      • Diaphragmatic pleura
      • Mediastinal pleura: forms a sleeve-like membranous tube called the root of the lung and covers the heart and great vessels of the heart
      • Cervical pleura: covered by the suprapleural membrane, a dome-shaped fascia attached to the 1st rib and C7 that serves as a site of insertion for some of the deep muscles of the neck
  • Visceral pleura:
    • Lines the outer surface of the lungs
    • Covers lung fissures
    • Not sensitive to pain
    • Continues with parietal pleura at the hilum of each lung
  • Recesses: named according to the points of reflection of the pleura
    • Costodiaphragmatic recess:
      • The largest recess
      • Found between the rib cage and the diaphragmatic portion of the pleura in each side of the thoracic cavity  
    • Costomedial recess: 
      • Found anteriorly between the rib cage and the mediastinum in each side of the thoracic cavity
      • The left recess is larger than the right due to the cardiac notch of the left lung.
    • Vertebromediastinal recess:
      • Found posteriorly between the rib cage, vertebral column, and the posterior mediastinum in each side of the thoracic cavity
Layers of thoracic wall - intercostal neurovascular bundle

Layers of the thoracic wall:
Note the double layer of pleura and the pleural cavity, separated from the rib cage by the endothoracic fascia.

Image by Lecturio. License: CC BY-NC-SA 4.0

Pleural cavity:

  • The potential space between the visceral pleura and parietal pleura (virtually nonexistent/undetectable)
  • Contains a small amount (0.1–0.2 mL/kg) of serous fluid that helps avoid friction between both pleurae
  • The surface tension of the fluid keeps the lungs expanded and in contact with the thoracic wall through the double layer of pleura.

Neurovasculature

Table: Neurovasculature of the pleura
IrrigationInnervation
Parietal pleuraCostal portion is supplied by:
  • Branches of the intercostal arteries
  • Branches of the internal thoracic arteries
Mediastinal portion is supplied by:
  • Bronchial arteries
  • Upper diaphragmatic arteries
  • Internal thoracic arteries
  • Mediastinal arteries
Cervical portion is supplied by: branches of the subclavian arteries
Diaphragmatic portion is supplied by: superficial part of the diaphragmatic microcirculation
Receives somatic afferent (sensory) innervation from:
  • Intercostal nerves (T1–T11):
    • Costal portion
    • Cervical portion
    • Peripheral diaphragmatic portion
  • Phrenic nerve (C3–C5):
    • Mediastinal portion
    • Central diaphragmatic portion
Visceral pleura
  • Bronchial circulation
  • Pulmonary circulation
Receives visceral afferent (autonomic) innervation from: pulmonary plexus
Blood supply of the pleurae

Blood supply of the pleurae:
The parietal pleura receives blood supply from the intercostal, diaphragmatic, mediastinal, and internal thoracic arteries. The visceral pleura receives blood supply from the bronchial and pulmonary vessels.

Image by Lecturio. License: CC BY-NC-SA 4.0

Clinical Relevance

Infectious disorders of the pleura

  • Pleural effusion: the accumulation of fluid between the layers of the parietal and visceral pleura. Caused by infection, malignancy, autoimmune disorders, or volume overload. Presents as chest pain, cough, and dyspnea. Classified as transudates or exudates, pleural effusions are usually diagnosed clinically, although imaging can confirm the diagnosis. Management is dependent on the underlying condition.
  • Pleuritis: also known as pleurisy, an inflammation of the pleura. Results in sudden and intense chest pain on inhalation and exhalation, and usually presents as part of pneumonia. The pain intensifies upon deep inspiration or coughing. Caused by infection, trauma, cardiac ischemia, and lung cancer. Management consists of pain control and the treatment of the underlying condition.

Traumatic disorders of the pleura

  • Pneumothorax: a life-threatening condition in which air collects in the pleural space, causing a partial or full collapse of the lung. Can be traumatic or spontaneous. Patients present with a sudden onset of sharp chest pain, dyspnea, and diminished breath sounds. Diagnosis is made with imaging, although tension pneumothorax is a clinical diagnosis. Management is based on its size and the stability of the patient.
  • Hemothorax: a collection of blood in the pleural cavity. Most commonly due to damage to the intercostal arteries from chest trauma. Presents with shortness of breath and chest pain. Physical exam findings include hypotension, tachycardia, decreased lung sounds, and dullness on percussion of the chest. Diagnosis is by upright chest X-ray. Management is usually with tube thoracostomy drainage. Thoracoscopic surgery or thoracotomy may be indicated in specific circumstances.

References

  1. Drake, R.L., Vogl, A.W., & Mitchell, A.W.M. (2014). Gray’s Anatomy for Students (3rd ed.). Philadelphia, PA:  Churchill Livingstone. 
  2. Standring, S. (2016). Gray’s anatomy. The Anatomical Basis of Clinical Practice (41st ed.). Edinburgh: Churchill Livingstone/Elsevier.

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