Mediastinum

The mediastinum (from Medieval Latin mediastinus, "midway"[2]) is the central compartment of the thoracic cavity surrounded by loose connective tissue, as an undelineated region that contains a group of structures within the thorax. The mediastinum contains the heart and its vessels, the esophagus, the trachea, the phrenic and cardiac nerves, the thoracic duct, the thymus and the lymph nodes of the central chest.

Mediastinum
3D rendering of a high resolution computed tomography of the thorax, with mediastinum marked in blue.
Mediastinum. The division between superior and inferior is at the sternal angle.
Details
Identifiers
Latin	mediastinum[1]
MeSH	D008482
TA	A07.1.02.101
FMA	9826
Anatomical terminology

Structure

The mediastinum can be seen from a frontal view in this illustration, with the superior mediastinum labeled a, and the pericardial cavity, which is part of the inferior mediastinum, labeled d.

The mediastinum lies within the thorax and is enclosed on the right and left by pleurae. It is surrounded by the chest wall in front, the lungs to the sides and the spine at the back. It extends from the sternum in front to the vertebral column behind, and contains all the organs of the thorax except the lungs. It is continuous with the loose connective tissue of the neck.

The mediastinum can be divided into an upper (or superior) and lower (or inferior) part:

• The superior mediastinum starts at the superior thoracic aperture and ends at the thoracic plane.
• The thoracic plane separates the superior and inferior mediastinum. It is a plane at the level of the sternal angle, and the intervertebral disc of T4–T5.[3][4][5]
• The inferior mediastinum from this level to the diaphragm. This lower part is subdivided into three regions, all relative to the pericardium – the anterior mediastinum being in front of the pericardium, the middle mediastinum contains the pericardium and its contents, and the posterior mediastinum being behind the pericardium.

Anatomists, surgeons, and clinical radiologists compartmentalize the mediastinum differently. For instance, in the radiological scheme of Felson, there are only three compartments (anterior, middle, and posterior), and the heart is part of the middle (inferior) mediastinum.[6]

Superior mediastinum

The superior mediastinum is bounded:

• superiorly by the thoracic inlet, the upper opening of the thorax;
• inferiorly by the transverse thoracic plane;
• laterally by the pleurae;
• anteriorly by the manubrium of the sternum;
• posteriorly by the first four thoracic vertebral bodies.

Contents

Mediastinum anatomy. Some mediastinal structures on a chest radiograph. Contents muscles origins of the Sternohyoidei and Sternothyreoidei lower ends of the Longi colli arteries aortic arch brachiocephalic artery thoracic portions of the left common carotid and the left subclavian veins brachiocephalic veins and upper half of the superior vena cava left highest intercostal vein nerves vagus nerve cardiac nerve superficial and deep cardiac plexuses phrenic nerve left recurrent laryngeal nerve trachea with paratracheal and tracheobronchial lymph nodes esophagus thoracic duct remains of the thymus some lymph glands anterior longitudinal ligament

Transverse-Thoracic plane

• The transverse thoracic plane separates the superior and inferior mediastinum. It is a plane at the level of the sternal angle, and the intervertebral disc of T4–T5.[3][4][5]

A number of structures occur at the level of the thoracic plane, which divides the superior and inferior mediastinum.

Inferior mediastinum

Anterior mediastinum

Is bounded:

• laterally by the pleurae;
• posteriorly by the pericardium;
• anteriorly by the sternum, the left transversus thoracis and the fifth, sixth, and seventh left costal cartilages.

Contents
Contents A quantity of loose areolar tissue Some lymphatic vessels which ascend from the convex surface of the liver Two or three anterior mediastinal lymph nodes The small mediastinal branches of the internal thoracic artery Thymus (involuted in adults) superior and inferior sternopericardial ligaments

Middle mediastinum

Bounded: pericardial sac – It contains the vital organs and is classified into the serous and fibrous pericardium.

Contents
Contents the heart enclosed in the pericardium the ascending aorta the lower half of the superior vena cava with the azygos vein opening into it the bifurcation of the trachea and the two bronchi the pulmonary trunk dividing into its two branches the right and left pulmonary veins the phrenic nerves some bronchial lymphatic glands pericardiocophrenic vessels

Posterior mediastinum

Is bounded:

• Anteriorly by (from above downwards): bifurcation of trachea; pulmonary vessels; fibrous pericardium and posterior sloping surface of diaphragm
• Inferiorly by the thoracic surface of the diaphragm (below);
• Superiorly by the transverse thoracic plane;
• Posteriorly by the bodies of the vertebral column from the lower border of the fifth to the twelfth thoracic vertebra (behind);
• Laterally by the mediastinal pleura (on either side).

Contents
artery thoracic part of the descending aorta veins azygos vein the hemiazygos vein and the accessory hemiazygos vein nerves vagus nerve splanchnic nerves sympathetic chain esophagus thoracic duct some lymph glands

• 
  A transverse section of the thorax, showing the contents of the middle and the posterior mediastinum.

Clinical significance

Mediastinal adenopathy

The mediastinum is frequently the site of involvement of various tumors:

• Anterior mediastinum: substernal thyroid goiters, lymphoma, thymoma, and teratoma.
• Middle mediastinum: lymphadenopathy, metastatic disease such as from small cell carcinoma from the lung.
• Posterior mediastinum: Neurogenic tumors, either from the nerve sheath (mostly benign) or elsewhere (mostly malignant).

Mediastinitis is inflammation of the tissues in the mediastinum, usually bacterial and due to rupture of organs in the mediastinum. As the infection can progress very quickly, this is a serious condition.

Pneumomediastinum is the presence of air in the mediastinum, which in some cases can lead to pneumothorax, pneumoperitoneum, and pneumopericardium if left untreated. However, that does not always occur and sometimes those conditions are actually the cause, not the result, of pneumomediastinum. These conditions frequently accompany Boerhaave syndrome, or spontaneous esophageal rupture.

Widened mediastinum

Widened mediastinum
Other names	Mediastinal widening
Widened mediastinum in a patient with achalasia

Widened mediastinum/mediastinal widening is where the mediastinum has a width greater than 6 cm on an upright PA chest X-ray or 8 cm on supine AP chest film.[7]

A widened mediastinum can be indicative of several pathologies:[8][9]

• aortic aneurysm[10]
• aortic dissection[11]
• aortic unfolding
• aortic rupture
• hilar lymphadenopathy
• anthrax inhalation - a widened mediastinum was found in 7 of the first 10 victims infected by anthrax (Bacillus anthracis) in 2001.[12]
• esophageal rupture - presents usually with pneumomediastinum and pleural effusion. It is diagnosed with water-soluble swallowed contrast.
• mediastinal mass
• mediastinitis
• cardiac tamponade[13]
• pericardial effusion
• thoracic vertebrae fractures in trauma patients.

See also

• Anthrax
• Mediastinum testis (unrelated structure in the scrotum)
• Mediastinal germ cell tumor
• Mediastinitis
• Mediastinal tumor

References

This article incorporates text in the public domain from page 1090 of the 20th edition of Gray's Anatomy (1918)

1. https://www.unifr.ch/ifaa/Public/EntryPage/TA98%20Tree/Alpha/All%20KWIC%20W%20LA.htm
2. "Mediastinum dictionary definition - mediastinum defined". www.yourdictionary.com.
3. Thoracic Wall, Pleura, and Pericardium – Dissector Answers Archived 2012-09-01 at the Wayback Machine
4. "Cell Biology and Anatomy - School of Medicine - University of South Carolina". dba.med.sc.edu.
5. "UAMS Department of Neurobiology and Developmental Sciences - Topographical Anatomy of the Thorax". anatomy.uams.edu.
6. Goodman, Lawrence. Felson's Principles of Chest Roentgenology.
7. D'Souza, Donna. "Thoracic aortic injury | Radiology Reference Article | Radiopaedia.org". radiopaedia.org.
8. Geusens; Pans, S.; Prinsloo, J.; Fourneau, I. (2005). "The widened mediastinum in trauma patients". European Journal of Emergency Medicine. 12 (4): 179–184. doi:10.1097/00063110-200508000-00006. PMID 16034263.
9. Richardson; Wilson, M. E.; Miller, F. B. (1990). "The widened mediastinum. Diagnostic and therapeutic priorities". Annals of Surgery. 211 (6): 731–736, discussion 736–7. doi:10.1097/00000658-199006000-00012. PMC 1358125. PMID 2357135.
10. Chandra S, Laor YG (April 1975). "Lung scan and wide mediastinum". J. Nucl. Med. 16 (4): 324–5. PMID 1113190.
11. von Kodolitsch Y, Nienaber C, Dieckmann C, Schwartz A, Hofmann T, Brekenfeld C, Nicolas V, Berger J, Meinertz T (2004). "Chest radiography for the diagnosis of acute aortic syndrome". Am J Med. 116 (2): 73–7. doi:10.1016/j.amjmed.2003.08.030. PMID 14715319.
12. Jernigan JA, Stephens DS, Ashford DA, et al. (2001). "Bioterrorism-related inhalational anthrax: the first 10 cases reported in the United States". Emerging Infect. Dis. 7 (6): 933–44. doi:10.3201/eid0706.010604. PMC 2631903. PMID 11747719.
13. Gideon P. Naudé; Fred S. Bongard; Demetrios Demetriades (2003). Trauma secrets. Elsevier Health Sciences. pp. 95–. ISBN 978-1-56053-506-5. Retrieved 19 April 2010.

External links

• Anatomy figure: 21:01-03 at Human Anatomy Online, SUNY Downstate Medical Center – "Divisions of the mediastinum."
• Anatomy figure: 21:02-03 at Human Anatomy Online, SUNY Downstate Medical Center – "The anatomical divisions of the inferior mediastinum."
• thoraxlesson3 at The Anatomy Lesson by Wesley Norman (Georgetown University) – "Subdivisions of the Thoracic Cavity"

Classification	D ICD-9-CM: 519.3 MeSH: D008482 DiseasesDB: 29459