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Mediastinum

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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
TA98	A07.1.02.101
TA2	3333
FMA	9826
Anatomical terminology [edit on Wikidata]

The mediastinum (from Medieval Latin: mediastinus, lit. 'midway';^[2]pl.: mediastina) is the central compartment of the thoracic cavity. Surrounded by loose connective tissue, it is an undelineated region that contains a group of structures within the thorax, namely 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.

Anatomy[edit]

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.^[3][4] It contains all the organs of the thorax except the lungs.^[4][5] 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 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.^[6]

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.^{[7][page needed]}

Thoracic plane[edit]

The transverse thoracic plane, thoracic plane, plane of Louisorplane of Ludwig is an important anatomical plane at the level of the sternal angle and the T4/T5 intervertebral disc.^[8][9][10] It serves as an imaginary boundary that separates the superior and inferior mediastinum.^[8][9][10]

A number of important anatomical structures and transitions occur at the level of the thoracic plane, including:

• The carinal bifurcation of the trachea into the left and right main bronchi.
• The left recurrent laryngeal nerve branching off the left vagus nerve and hooking under the ligamentum arteriosum between the aortic arch above and the pulmonary trunk below.
• The starting of the cardiac plexus.
• The azygos vein arching over the right main bronchus and joining into the superior vena cava.
• The thoracic duct crossing the midline from right to left behind the esophagus
• The end of the pretracheal and prevertebral fasciae.

Superior mediastinum[edit]

The superior mediastinum is bounded:

• superiorly by the thoracic inlet, the upper opening of the thorax;
• inferiorly by the transverse thoracic plane. which is an imaginary plane passing from the sternal angle anteriorly to the lower border of the body of the 4th thoracic vertebra posteriorly;
• laterally by the pleurae;
• anteriorly by the manubrium of the sternum;
• posteriorly by the first four thoracic vertebral bodies.

Contents

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

Inferior mediastinum[edit]

Anterior inferior mediastinum[edit]

Is bounded:

• laterally by the pleurae;
• posteriorly by the pericardium;^[4]
• anteriorly by the sternum,^[4] the left transversus thoracis and the fifth, sixth, and seventh left costal cartilages.

Middle inferior mediastinum[edit]

Bounded: pericardial sac – It contains the vital organs and is classified into the serous and fibrous pericardium.^[4]

Posterior inferior mediastinum[edit]

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);^[4]
• Laterally by the mediastinal pleura (on either side).

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

Clinical significance[edit]

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).

Mediastinitisisinflammation 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.

Widening[edit]

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.^[11]

A widened mediastinum can be indicative of several pathologies:^[12][13]

• aortic aneurysm^[14]
• aortic dissection^[15]
• 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.^[16]
• esophageal rupture - presents usually with pneumomediastinum and pleural effusion. It is diagnosed with water-soluble swallowed contrast.
• mediastinal mass
• mediastinitis
• cardiac tamponade^[17]
• pericardial effusion
• thoracic vertebrae fractures in trauma patients.

See also[edit]

• Mediastinum testis (unrelated structure in the scrotum)
• Mediastinal germ cell tumor
• Mediastinitis
• Mediastinal tumor
• List of anatomy mnemonics#Mediastinum

References[edit]

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

External links[edit]

Look up mediastinum in Wiktionary, the free dictionary.

• 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"