Thoracic cavity

Last updated: July 5, 2023

Summarytoggle arrow icon

The thoracic cavity is a hollow space surrounded by the rib cage and the diaphragm that contains the heart, lungs, esophagus, thymus, sympathetic trunk, and the great vessels. It comprises three compartments: two pleural cavities and the mediastinum, which is located behind the sternum. The mediastinum is divided into the superior and inferior mediastinum, the latter of which is further subdivided into the anterior, middle, and posterior mediastinum. Inflammation of the mediastinum (mediastinitis) can result from spreading retropharyngeal infections or contamination from perforated mediastinal organs. The mediastinum is also a potential site for teratoma, lymphoma, thymoma, and thyroid neoplasm. The pleural cavity is the potential space between the parietal pleura (which covers the thoracic wall and the mediastinum) and the visceral pleura (which lines the lung). The pleura secretes fluid that prevents the development of friction between the two pleural membranes. Excessive build-up of fluid in the pleural cavity results in pleural effusion, while the entry of air results in pneumothorax. The diaphragm is a musculotendinous structure that separates the thoracic cavity from the abdominal cavity. It has hiatuses for the passage of the inferior vena cava (caval hiatus), esophagus (esophageal hiatus), and the aorta (aortic hiatus) at the 8th, 10th, and 12th thoracic vertebrae respectively. The diaphragm is innervated by the phrenic nerve. Phrenic nerve palsy or injury to the diaphragm results in impaired respiration.

Overviewtoggle arrow icon

Mediastinumtoggle arrow icon


Compartments of the mediastinum [1]
Structure Boundaries Organs Vessels Nerves Causes of mediastinal masses
Superior mediastinum
  • Superior: first rib
  • Inferior: line that courses from the sternal angle to the 4th and 5th vertebral levels (transthoracic plane)
Inferior mediastinum Anterior mediastinum
  • NA
Middle mediastinum
Posterior mediastinum

The most common causes of inflammation of the mediastinal space (mediastinitis) include spreading of retropharyngeal infections into the mediastinum, chest trauma, and perforation of mediastinal organs, e.g., the esophagus in the course of a gastroscopy or due to esophageal cancer.

The trachea bifourcates at the level of T4.

The 4 T's of a mediastinal mass: Thymoma, Teratoma (and other germ cell tumors), Thyroid neoplasm, and Terrible lymphoma.

Vasculature of the mediastinum [1]


The pulmonary trunk, which is located in the middle mediastinum and conveys deoxygenated blood to the lungs, is discussed in “Airways and lungs”.

Branches of aorta in thoracic cavity
Structure Anatomy Location Branches Supplies
Ascending aorta
Arch of the aorta
  • Head
  • Upper extremities

Thoracic aorta

(Part of the descending aorta)

  • Bronchial arteries
  • Mediastinal arteries
  • Esophageal arteries
  • Pericardial arteries
  • Superior phrenic arteries
  • Posterior intercostal arteries (9 pairs)
  • Subcostal arteries


The pulmonary veins, which are located in the middle mediastinum and transfer oxygenated blood from the lungs to the heart, are discussed in “Airways and lungs”. Cavocaval anastomoses are discussed in “Abdominal cavity”.

Veins in the thoracic cavity
Structure Formation Characteristics Tributaries
Superior vena cava (SVC)
Brachiocephalic veins
Azygos venous system

Azygos vein

Hemiazygos vein

  • Formed by the ascending lumbar and left subcostal veins

Accessory hemiazygos vein

The azygos vein connects the inferior and superior vena cava and can be an alternative pathway for deoxygenated blood to return to the right atrium if the SVC or the IVC are obstructed.


See “Thoracic duct” and “Right lymphatic duct.”

Pleuratoggle arrow icon

Overview [1]

Definition: Pleura is a thin double layer of tissue that surrounds the lungs and the thoracic wall and divided into a visceral and parietal layer.

Layers of pleura
Structure Parietal pleura Visceral pleura
  • Lines the inner surface of the thoracic wall and the mediastinum
  • Divided into the following parts
  • Lines the outer surface of the lungs and follows the contour of the lungs, including the fissures
Blood supply
Clinical significance
  • Intrapulmonary pathologies (e.g., lung cancer) do not cause pain and remain unnoticed for a long time.

Pleural cavity [1]

  • Location: potential space between the parietal and visceral pleura of the lungs
  • Content: pleural fluid (secreted by serous membranes in the pleura)
    • Lubricates and prevents friction between the parietal and visceral pleura
    • Produces a surface tension that draws the two pleura layers together, ensuring simultaneous extension of the thorax and lungs during respiration
  • Recesses
    • Costomediastinal recess: region where the mediastinal and costal pleura meet
    • Costodiaphragmatic recess: region where the costal and diaphragmatic pleura meet

If air enters the pleural cavity, the surface tension between the parietal and visceral pleura of the lungs is lost, letting the lungs collapse due to their natural tendency to collapse or recoil (pneumothorax).

Excessive fluid in the pleural cavity results in pleural effusion.

Diaphragmtoggle arrow icon

Overview [1]

  • Structure
    • C-shaped musculotendinous structure that separates the thoracic cavity from the abdominal cavity
    • Forms a dome between the two cavities, with the superior surface making the floor of the thoracic cavity, and the inferior surface making the roof of the abdominal cavity
    • Anatomically, the diaphragm is divided into a right and left hemidiaphragm; however, the diaphragm is a continuous structure.
    • The right hemidiaphragm is higher than the left due to the presence of the liver.
  • Function
    • Separates the thoracic cavity from the abdominal cavity
    • Key muscle of inspiration

Parts of the diaphragm [1]

Crura of the diaphragm

Costal diaphragm

Central tendon of the diaphragm

  • Location: point of convergence of the peripherally located muscles that make up the diaphragm

Structures passing through the diaphragm

Openings of the diaphragm
Opening Level Structure
Caval hiatus
  • T8
Esophageal hiatus
  • T10
Aortic hiatus
  • T12

I ate (read 8) ten Eggs At twelve: Inferior vena cava passes the diaphragm at T8, the Esophagus at T10, and the Aorta at T12.

The vagus nerve (CN X) passes through the diaphragm at T10.

The protrusion of an abdominal structure/organ into the thorax through a lax diaphragmatic esophageal hiatus is referred to as a hiatal hernia.

Vasculature and innervation of the diaphragm

Arterial supply
Venous drainage

C3, C4, C5 keeps the diaphragm alive.

Injuries to the diaphragm or phrenic nerve palsies result in respiratory abnormalities because the diaphragm is the primary muscle of respiration.

Clinical significancetoggle arrow icon


Brachiocephalic vein obstruction [4][5]




Referencestoggle arrow icon

  1. Standring S. Gray's Anatomy: The Anatomical Basis of Clinical Practice. Elsevier Health Sciences ; 2016
  2. Batori M, Chatelou E, Straniero A. Surgical treatment of retrosternal goiter.. Eur Rev Med Pharmacol Sci. ; 11 (4): p.265-8.
  3. Abhishek K, Ejazi M, Hashim Z, Chaudhary R, Niharika K. Multiple myeloma with different thoracic manifestations: Case series. Indian Journal of Respiratory Care. 2018; 7 (2): p.108.doi: 10.4103/ijrc.ijrc_11_18 . | Open in Read by QxMD
  4. Ko S-F, Huang C-C, Ng S-H, et al. Imaging of the brachiocephalic vein. AJR. 2008; 191 (3): p.897-907.doi: 10.2214/ajr.07.3552 . | Open in Read by QxMD
  5. Guo X, Shi Y, Xie H, et al. Left innominate vein stenosis in an asymptomatic population: a retrospective analysis of 212 cases. Eur J Med Res. 2017; 22 (1).doi: 10.1186/s40001-017-0243-3 . | Open in Read by QxMD
  6. Mediastinal Tumors. Updated: January 1, 2017. Accessed: January 3, 2019.
  7. Mueller DK. Neurogenic Tumors of the Mediastinum. In: Mancini MC, Neurogenic Tumors of the Mediastinum. New York, NY: WebMD. Updated: November 2, 2017. Accessed: January 3, 2019.

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