The mediastinum (from ) is the central compartment of the

thoracic cavity The thoracic cavity (or chest cavity) is the chamber of the body of vertebrates that is protected by the thoracic wall (rib cage and associated skin, muscle, and fascia). The central compartment of the thoracic cavity is the mediastinum. There ...

. Surrounded by

loose connective tissue Loose connective tissue, sometimes called areolar tissue, is a cellular connective tissue with thin and relatively sparse collagen fibers. Its ground substance occupies more volume than the fibers do. It has a viscous to gel-like consisten ...

, it is an undelineated region that contains a group of structures within the

thorax The thorax or chest is a part of the anatomy of humans, mammals, and other tetrapod animals located between the neck and the abdomen. In insects, crustaceans, and the extinct trilobites, the thorax is one of the three main divisions of the ...

, namely the

heart The heart is a muscular organ found in most animals. This organ pumps blood through the blood vessels of the circulatory system. The pumped blood carries oxygen and nutrients to the body, while carrying metabolic waste such as carbon diox ...

and its vessels, the

esophagus The esophagus (American English) or oesophagus (British English; both ), non-technically known also as the food pipe or gullet, is an organ in vertebrates through which food passes, aided by peristaltic contractions, from the pharynx to the ...

, the

trachea The trachea, also known as the windpipe, is a cartilaginous tube that connects the larynx to the bronchi of the lungs, allowing the passage of air, and so is present in almost all air-breathing animals with lungs. The trachea extends from th ...

, the phrenic and

cardiac nerve The cardiac nerves are autonomic nerves which supply the heart. They include: * Superior cardiac nerve (nervus cardiacus cervicalis superior) * Middle cardiac nerve (nervus cardiacus cervicalis medius) * Inferior cardiac nerve The inferior cardiac ...

s, the thoracic duct, the

thymus The thymus is a specialized primary lymphoid organ of the immune system. Within the thymus, thymus cell lymphocytes or ''T cells'' mature. T cells are critical to the adaptive immune system, where the body adapts to specific foreign invaders. ...

and the

lymph nodes A lymph node, or lymph gland, is a kidney-shaped organ of the lymphatic system and the adaptive immune system. A large number of lymph nodes are linked throughout the body by the lymphatic vessels. They are major sites of lymphocytes that incl ...

of the central chest.

Anatomy

The mediastinum lies within the

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 The sternum or breastbone is a long flat bone located in the central part of the chest. It connects to the ribs via cartilage and forms the front of the rib cage, thus helping to protect the heart, lungs, and major blood vessels from injury. ...

in front to the

vertebral column The vertebral column, also known as the backbone or spine, is part of the axial skeleton. The vertebral column is the defining characteristic of a vertebrate in which the notochord (a flexible rod of uniform composition) found in all chordate ...

behind. It contains all the organs of the thorax except the lungs. It is continuous with the loose connective tissue of the

neck The neck is the part of the body on many vertebrates that connects the head with the torso. The neck supports the weight of the head and protects the nerves that carry sensory and motor information from the brain down to the rest of the body. In ...

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 Diaphragm may refer to: Anatomy * Thoracic diaphragm, a thin sheet of muscle between the thorax and the abdomen * Pelvic diaphragm or pelvic floor, a pelvic structure * Urogenital diaphragm or triangular ligament, a pelvic structure Other * Diap ...

. This lower part is subdivided into three regions, all relative to the

pericardium The pericardium, also called pericardial sac, is a double-walled sac containing the heart and the roots of the great vessels. It has two layers, an outer layer made of strong connective tissue (fibrous pericardium), and an inner layer made of ...

– 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.

Anatomist Anatomy () is the branch of biology concerned with the study of the structure of organisms and their parts. Anatomy is a branch of natural science that deals with the structural organization of living things. It is an old science, having it ...

s, 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.

Thoracic plane

The transverse thoracic plane, thoracic plane, plane of Louis or plane of Ludwig is an important anatomical plane at the level of the sternal angle and the T4/T5 intervertebral disc. It serves as an imaginary boundary that separates the superior and inferior mediastinum.Thoracic Wall, Pleura, and Pericardium – Dissector Answers
A number of important anatomical structures and transitions occur at the level of the thoracic plane, including: * The carinal bifurcation of the

into the left and right main bronchi. * The left recurrent laryngeal nerve branching off the left

vagus nerve The vagus nerve, also known as the tenth cranial nerve, cranial nerve X, or simply CN X, is a cranial nerve that interfaces with the parasympathetic control of the heart, lungs, and digestive tract. It comprises two nerves—the left and rig ...

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 The azygos vein is a vein running up the right side of the thoracic vertebral column draining itself towards the superior vena cava. It connects the systems of superior vena cava and inferior vena cava and can provide an alternative path for blo ...

arching over the right main bronchus and joining into the

superior vena cava The superior vena cava (SVC) is the anatomical terms of location#Superior and inferior, superior of the two venae cavae, the great vein, venous trunks that return deoxygenated blood from the circulatory system, systemic circulation to the atrium ...

. * The thoracic duct crossing the midline from right to left behind the

* The end of the pretracheal and prevertebral fasciae.

Superior

The superior mediastinum is bounded: * ''superiorly'' by the thoracic inlet, the upper opening of the

; * ''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 The spinal column, a defining synapomorphy shared by nearly all vertebrates, Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristi ...

Mediastinal structures on chest X-ray, annotated

;Contents * muscles ** origins of the

Sternohyoidei The sternohyoid muscle is a thin, narrow muscle attaching the hyoid bone to the sternum. It is one of the paired strap muscles of the infrahyoid muscles. It is supplied by the ansa cervicalis. It depresses the hyoid bone. Structure The sternohyo ...

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 The left and right brachiocephalic veins (previously called innominate veins) are major veins in the upper chest, formed by the union of each corresponding internal jugular vein and subclavian vein. This is at the level of the sternoclavicular j ...

and ** upper half of the

** left

highest intercostal vein The supreme intercostal vein (highest intercostal vein) is a paired vein that drains the first intercostal space on its corresponding side. It usually drains into the brachiocephalic vein. Alternatively, it drains into the superior intercostal ...

* nerves **

** superficial and deep cardiac plexuses ** phrenic nerve ** left recurrent laryngeal nerve *

with paratracheal and tracheobronchial lymph nodes *

* thoracic duct * remains of the

* some lymph glands * anterior longitudinal ligament

Inferior

;Anterior mediastinum Is bounded: * ''laterally'' by the pleurae; * ''posteriorly'' by the

; * ''anteriorly'' by the

, the left transversus thoracis and the fifth, sixth, and seventh left costal cartilages. ;Contents * A quantity of loose areolar tissue * Some lymphatic vessels which ascend from the convex surface of the

liver The liver is a major organ only found in vertebrates which performs many essential biological functions such as detoxification of the organism, and the synthesis of proteins and biochemicals necessary for digestion and growth. In humans, it ...

* Two or three anterior mediastinal

* The small mediastinal branches of the internal thoracic artery *

Thymus The thymus is a specialized primary lymphoid organ of the immune system. Within the thymus, thymus cell lymphocytes or ''T cells'' mature. T cells are critical to the adaptive immune system, where the body adapts to specific foreign invaders. ...

(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 * the

enclosed in the

* the ascending aorta * the lower half of the

with the

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 The phrenic nerve is a mixed motor/sensory nerve which originates from the C3-C5 spinal nerves in the neck. The nerve is important for breathing because it provides exclusive motor control of the diaphragm, the primary muscle of respiration. ...

* some bronchial lymphatic glands * pericardiocophrenic vessels ;Posterior mediastinum Is bounded: * Anteriorly by (from above downwards): bifurcation of

; pulmonary vessels; fibrous pericardium and posterior sloping surface of

* Inferiorly by the thoracic surface of the

(below); * Superiorly by the transverse thoracic plane; * Posteriorly by the bodies of the

from the lower border of the fifth to the twelfth

thoracic vertebra In vertebrates, thoracic vertebrae compose the middle segment of the vertebral column, between the cervical vertebrae and the lumbar vertebrae. In humans, there are twelve thoracic vertebrae and they are intermediate in size between the cervica ...

(behind); * Laterally by the mediastinal pleura (on either side). * artery ** thoracic part of the descending aorta * veins **

** the hemiazygos vein and the accessory hemiazygos vein * nerves **

** splanchnic nerves ** sympathetic chain *

* thoracic duct * some lymph glands File:Gray968.png , A transverse section of the

, showing the contents of the

middle Middle or The Middle may refer to: * Centre (geometry), the point equally distant from the outer limits. Places * Middle (sheading), a subdivision of the Isle of Man * Middle Bay (disambiguation) * Middle Brook (disambiguation) * Middle Creek (d ...

and the posterior mediastinum.

Clinical significance

The mediastinum is frequently the site of involvement of various tumors: * ''Anterior mediastinum'': substernal

thyroid The thyroid, or thyroid gland, is an endocrine gland in vertebrates. In humans it is in the neck and consists of two connected lobes. The lower two thirds of the lobes are connected by a thin band of tissue called the thyroid isthmus. The t ...

goiter A goitre, American and British English spelling differences#re er, or goiter, is a swelling in the neck resulting from an enlarged thyroid, thyroid gland. A goitre can be associated with a thyroid that is not functioning properly. Worldwide, over ...

lymphoma Lymphoma is a group of blood and lymph tumors that develop from lymphocytes (a type of white blood cell). In current usage the name usually refers to just the cancerous versions rather than all such tumours. Signs and symptoms may include enl ...

, 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 Inflammation (from la, wikt:en:inflammatio#Latin, inflammatio) is part of the complex biological response of body tissues to harmful stimuli, such as pathogens, damaged cells, or Irritation, irritants, and is a protective response involving im ...

of the tissues in the mediastinum, usually

bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were am ...

l 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 A pneumothorax is an abnormal collection of air in the pleural space between the lung and the chest wall. Symptoms typically include sudden onset of sharp, one-sided chest pain and shortness of breath. In a minority of cases, a one-way valve ...

pneumoperitoneum Pneumoperitoneum is pneumatosis (abnormal presence of air or other gas) in the peritoneal cavity, a potential space within the abdominal cavity. The most common cause is a perforated abdominal organ, generally from a perforated peptic ulcer, ...

, 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

''Widened mediastinum/mediastinal widening'' is where the mediastinum has a width greater than 6 cm on an upright PA

chest X-ray A chest radiograph, called a chest X-ray (CXR), or chest film, is a projection radiograph of the chest used to diagnose conditions affecting the chest, its contents, and nearby structures. Chest radiographs are the most common film taken in me ...

or 8 cm on supine AP chest film. A widened mediastinum can be indicative of several pathologies: *

aortic aneurysm An aortic aneurysm is an enlargement (dilatation) of the aorta to greater than 1.5 times normal size. They usually cause no symptoms except when ruptured. Occasionally, there may be abdominal, back, or leg pain. The prevalence of abdominal aorti ...

* aortic dissection *

aortic unfolding Aortic unfolding is an abnormality visible on a chest X-ray, that shows widening of the mediastinum which may mimic the appearance of a thoracic aortic aneurysm. With aging, the ascending portion of the thoracic aorta increases in length by appro ...

* 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. * esophageal rupture - presents usually with pneumomediastinum and

pleural effusion 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 ...

. It is diagnosed with water-soluble swallowed contrast. * mediastinal mass * mediastinitis * cardiac tamponade *

pericardial effusion 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 ...

* thoracic vertebrae fractures in trauma patients.

References

External links

* – "Divisions of the mediastinum." * – "The anatomical divisions of the inferior mediastinum." * – "Subdivisions of the Thoracic Cavity" {{Authority control Thoracic cavity