View source for Mediastinum

{{Short description|Central part of the thoracic cavity}}
{{About|the body cavity within the thorax|the septum of the testis|mediastinum testis}}
{{More citations needed|date=September 2014}}
{{Infobox anatomy
| Name        = Mediastinum
| Latin       = mediastinum<ref>{{Cite web|url=https://ifaa.unifr.ch/Public/EntryPage/TA98%20Tree/Alpha/All%20KWIC%20W%20LA.htm|title=A index W LA}}</ref>
| Image       = Body Cavities Frontal view labeled.jpg
| Caption     = Frontal view of the body cavities: '''superior mediastinum''' labeled '''a''', and the [[pericardial cavity]], which is part of the '''inferior mediastinum''', labeled '''d'''
| Image2      = Mediastinum.png
| Caption2    = Mediastinum, lateral view. The division between superior and inferior is at the [[sternal angle]].
| Width       = 260
| System      =
}}

The '''mediastinum''' (from {{Langx|la-x-medieval|mediastinus|lit=midway}};<ref>{{cite web|url=http://www.yourdictionary.com/mediastinum|title=Mediastinum dictionary definition - mediastinum defined|website=www.yourdictionary.com}}</ref>{{plural form}}: '''mediastina''') is the central compartment of the [[thoracic cavity]]. Surrounded by [[loose connective tissue]], it is a region that contains vital organs and structures within the [[thorax]], mainly the [[heart]] and its vessels, the [[esophagus]], the [[trachea]], the [[vagus nerve|vagus]], [[phrenic nerve|phrenic]] and [[cardiac nerve]]s, the [[thoracic duct]], the [[thymus]] and the [[lymph nodes]] of the central chest.

== Anatomy ==
[[File:CT-Thorax-5.0-B31f-HD.ogg|thumb|left|CT thorax (axial, mediastinal window)]]
The mediastinum lies within the [[thorax]] and is enclosed on the right and left by [[pulmonary pleurae|pleurae]]. It is surrounded by the chest wall in front, the [[lung]]s to the sides and the [[Spine (anatomy)|spine]] at the back. It extends from the [[sternum]] in front to the [[vertebral column]] behind.<ref>{{Citation|last1=Fong|first1=K. M.|title=TUMORS, MALIGNANT {{!}} Carcinoma, Lymph Node Involvement|date=2006-01-01|url=http://www.sciencedirect.com/science/article/pii/B0123708796004075|encyclopedia=Encyclopedia of Respiratory Medicine|pages=366–373|editor-last=Laurent|editor-first=Geoffrey J.|place=Oxford|publisher=Academic Press|language=en|doi=10.1016/b0-12-370879-6/00407-5|isbn=978-0-12-370879-3|access-date=2020-11-17|last2=Windsor|first2=M.|last3=Bowman|first3=R. V.|last4=Duhig|first4=E.|editor2-last=Shapiro|editor2-first=Steven D.|url-access=subscription}}</ref><ref name=":0">{{Citation|last=Ng|first=Wai-Kuen|title=CHAPTER 26 - Mediastinum|date=2008-01-01|url=http://www.sciencedirect.com/science/article/pii/B9781416042082100260|work=Comprehensive Cytopathology (Third Edition)|pages=773–809|editor-last=Bibbo|editor-first=Marluce|place=Edinburgh|publisher=W.B. Saunders|language=en|isbn=978-1-4160-4208-2|access-date=2020-11-17|editor2-last=Wilbur|editor2-first=David}}</ref> It contains all the organs of the thorax except the lungs.<ref name=":0" /><ref>{{Citation|last1=Cheng|first1=Guang-Shing|title=83 - Mediastinal Tumors and Cysts|date=2016-01-01|url=http://www.sciencedirect.com/science/article/pii/B978145573383500083X|work=Murray and Nadel's Textbook of Respiratory Medicine (Sixth Edition)|pages=1478–1495.e38|editor-last=Broaddus|editor-first=V. Courtney|place=Philadelphia|publisher=W.B. Saunders|language=en|doi=10.1016/b978-1-4557-3383-5.00083-x|isbn=978-1-4557-3383-5|access-date=2020-11-17|last2=Varghese|first2=Thomas K.|last3=Park|first3=David R.|editor2-last=Mason|editor2-first=Robert J.|editor3-last=Ernst|editor3-first=Joel D.|editor4-last=King|editor4-first=Talmadge E.|url-access=subscription}}</ref> 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|thoracic plane]].
* The '''inferior mediastinum''' from this level to the [[Thoracic diaphragm|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.<ref>{{Citation|last=Breul|first=Rainer|title=The deeper fasciae of the neck and ventral torso|date=2012|url=https://linkinghub.elsevier.com/retrieve/pii/B9780702034251000416|work=Fascia: The Tensional Network of the Human Body|pages=45–52|publisher=Elsevier|language=en|doi=10.1016/b978-0-7020-3425-1.00041-6|isbn=978-0-7020-3425-1|access-date=2020-11-17|url-access=subscription}}</ref>

[[Anatomist]]s, [[surgeon]]s, 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.<ref>{{cite book|last=Goodman|first=Lawrence|title=Felson's Principles of Chest Roentgenology}}</ref>{{Page needed|date=January 2014}}

=== 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 [[thoracic vertebrae|T4/T5]] [[intervertebral disc]].<ref name="auto"/><ref name="sc.edu"/><ref name="uams.edu"/>  It serves as an imaginary boundary that separates the superior and inferior mediastinum.<ref name="auto">{{Cite web|url=http://anatomy.med.umich.edu/cardiovascular_system/thorax_wall_ans.html|archiveurl=https://web.archive.org/web/20120901215701/http://anatomy.med.umich.edu/cardiovascular_system/thorax_wall_ans.html|url-status=dead|title=Thoracic Wall, Pleura, and Pericardium – Dissector Answers|archivedate=September 1, 2012}}</ref><ref name="sc.edu">{{cite web|url=http://dba.med.sc.edu/GROSS/practise1.htm|title=Cell Biology and Anatomy - School of Medicine - University of South Carolina|website=dba.med.sc.edu|access-date=2014-09-22|archive-date=2006-09-05|archive-url=https://web.archive.org/web/20060905063147/http://dba.med.sc.edu/GROSS/practise1.htm|url-status=dead}}</ref><ref name="uams.edu">{{cite web|url=http://anatomy.uams.edu/AnatomyHTML/topogr_thorax.html|title=UAMS Department of Neurobiology and Developmental Sciences - Topographical Anatomy of the Thorax|website=anatomy.uams.edu|access-date=2014-09-22|archive-date=2004-08-17|archive-url=https://web.archive.org/web/20040817005148/http://anatomy.uams.edu/anatomyhtml/topogr_thorax.html|url-status=dead}}</ref>

A number of important anatomical structures and transitions occur at the level of the thoracic plane, including:
* The [[carina of trachea|carina]]l 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 fascia|pretracheal]] and [[prevertebral fascia]]e.

=== Superior mediastinum ===
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 [[pulmonary pleurae|pleurae]];
* ''anteriorly'' by the [[manubrium]] of the sternum;
* ''posteriorly'' by the first four thoracic [[vertebral bodies]].

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[[File:Mediastinum anatomy.jpg|thumb|Mediastinum anatomy.]]
[[File:Mediastinal structures on chest X-ray, annotated.jpg|thumb|300px|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 [[subclavian artery|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
{{collapse bottom}}

=== Inferior mediastinum ===
==== Anterior inferior mediastinum ====
Is bounded:

* ''laterally'' by the [[pleurae]];
* ''posteriorly'' by the [[pericardium]];<ref name=":0" />
* ''anteriorly'' by the [[Human sternum|sternum]],<ref name=":0" /> the left [[transversus thoracis]] and the fifth, sixth, and seventh left [[costal cartilages]].

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;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 [[Internal thoracic artery#Branches|mediastinal branches]] of the [[internal thoracic artery]]
* [[Thymus]] (involuted in adults)
*superior and inferior sternopericardial ligaments
{{collapse bottom}}

==== Middle inferior mediastinum ====
Bounded: [[pericardial sac]] – It contains the vital organs and is classified into the serous and fibrous pericardium.<ref name=":0" />

{{collapse top|title=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]]
* pericardiacophrenic vessels
{{collapse bottom}}

==== Posterior inferior mediastinum ====
Is bounded:
* Anteriorly by (from above downwards): bifurcation of [[trachea]]; pulmonary vessels; fibrous pericardium and posterior sloping surface of [[Thoracic diaphragm|diaphragm]]
* Inferiorly by the thoracic surface of the [[diaphragm (anatomy)|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);<ref name=":0" />
* Laterally by the [[mediastinal pleura]] (on either side).

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* artery
** [[Thoracic aorta|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]]
{{collapse bottom}}

<gallery>
File:Gray968.png |A transverse section of the [[thorax]], showing the contents of the [[middle mediastinum|middle]] and the [[posterior mediastinum]].
</gallery>

== Clinical significance ==
[[File:Mediastinaladenopathy.png|thumb|Mediastinal adenopathy]]
The mediastinum is frequently the site of involvement of various [[mediastinal tumor|tumors]]:

* ''Anterior mediastinum'': substernal [[Thyroid gland|thyroid]] [[goiter]]s, [[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 [[bacteria]]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]], [[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 [[Esophagus|esophageal]] rupture.

{{anchor|widening}}

=== Widening ===
{{Infobox medical condition (new)
|name= Widened mediastinum 
| synonyms = Mediastinal widening
|image= Achalasie im Thorax pa 001.png
|caption= Widened mediastinum in a patient with [[achalasia]] |
| pronounce       = 
| field           = 
| symptoms = | complications = | onset = | duration = | types = | causes = | risks = | diagnosis = | differential = | prevention = | treatment = | medication = | prognosis = | frequency = | deaths = }}

''Widened mediastinum/mediastinal widening'' is where the mediastinum has a width greater than 6&nbsp;cm on an upright PA [[chest X-ray]] or 8&nbsp;cm on supine AP chest film.<ref>{{cite web|last1=D'Souza|first1=Donna|title=Thoracic aortic injury {{!}} Radiology Reference Article {{!}} Radiopaedia.org|url=http://radiopaedia.org/articles/thoracic-aortic-injury|website=radiopaedia.org}}</ref>

A widened mediastinum can be indicative of several pathologies:<ref>{{Cite journal| pmid = 16034263| year = 2005| author1 = Geusens | first2 = S. | first3 = J. | first4 = I.| title = The widened mediastinum in trauma patients| volume = 12| issue = 4| pages = 179–184| journal = European Journal of Emergency Medicine | last2 = Pans| last3 = Prinsloo| last4 = Fourneau | doi=10.1097/00063110-200508000-00006}}</ref><ref>{{Cite journal| pmid = 2357135| year = 1990| author1 = Richardson | first2 = M. E. | first3 = F. B.| title = The widened mediastinum. Diagnostic and therapeutic priorities| volume = 211| issue = 6| pages = 731–736; discussion 736–7| pmc = 1358125| journal = Annals of Surgery| last2 = Wilson| last3 = Miller| doi = 10.1097/00000658-199006000-00012}}</ref>

* [[aortic aneurysm]]<ref name="pmid1113190">{{Cite journal|vauthors=Chandra S, Laor YG |title=Lung scan and wide mediastinum |journal=J. Nucl. Med. |volume=16 |issue=4 |pages=324–5 |date=April 1975 |pmid=1113190 |url=http://jnm.snmjournals.org/cgi/pmidlookup?view=long&pmid=1113190}}</ref>
* [[aortic dissection]]<ref>{{Cite journal| vauthors = von Kodolitsch Y, Nienaber C, Dieckmann C, Schwartz A, Hofmann T, Brekenfeld C, Nicolas V, Berger J, Meinertz T | title = Chest radiography for the diagnosis of [[acute aortic syndrome]] | journal = Am J Med | volume = 116 | issue = 2 | pages = 73–7 | year = 2004 | pmid = 14715319 | doi = 10.1016/j.amjmed.2003.08.030}}</ref>
* [[aortic unfolding]]
* [[aortic rupture]]
* [[hilar lymphadenopathy]]
* [[anthrax|anthrax inhalation]] - a widened mediastinum was found in 7 of the first 10 victims infected by anthrax (''Bacillus anthracis'') in 2001.<ref name="pmid11747719">{{Cite journal |vauthors=Jernigan JA, Stephens DS, Ashford DA, etal |title=Bioterrorism-related inhalational anthrax: the first 10 cases reported in the United States |journal=Emerging Infect. Dis. |volume=7 |issue=6 |pages=933–44 |year=2001 |pmid=11747719 |doi=10.3201/eid0706.010604 |pmc=2631903}}</ref>
*[[esophageal rupture]] - presents usually with [[pneumomediastinum]] and [[pleural effusion]]. It is diagnosed with water-soluble swallowed contrast.
*[[mediastinal mass]]
*[[mediastinitis]]
*[[cardiac tamponade]]<ref name="NaudéBongard2003">{{Cite book|author1=Gideon P. Naudé|author2=Fred S. Bongard|author3=Demetrios Demetriades|title=Trauma secrets|url=https://books.google.com/books?id=joAIOFKkfRcC&pg=PA95|access-date=19 April 2010|year=2003|publisher=Elsevier Health Sciences|isbn=978-1-56053-506-5|pages=95–}}</ref>
*[[pericardial effusion]]
*[[thoracic vertebrae fracture]]s in trauma patients.

== See also ==
* [[Mediastinum testis]] (unrelated structure in the [[scrotum]])
* [[Mediastinal germ cell tumor]]
* [[Mediastinitis]]
* [[Mediastinal tumor]]
* [[List of anatomy mnemonics#Mediastinum]]

== References ==
{{Gray's}}
{{Reflist}}

== External links ==
{{wiktionary}}
* {{SUNYAnatomyFigs|21|01|03}} – "Divisions of the mediastinum."
* {{SUNYAnatomyFigs|21|02|03}} – "The anatomical divisions of the inferior mediastinum."
* {{NormanAnatomy|thoraxlesson3}} – "Subdivisions of the Thoracic Cavity"

{{Medical resources
|   DiseasesDB     = 29459 
|   ICD10          =  
|   ICD9           = {{ICD9|519.3}} 
|   ICDO           = 
|   OMIM           = 
|   MedlinePlus    = 
|   eMedicineSubj  = 
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{{Thoracic cavity}}
{{Portal bar|Anatomy}}
{{Authority control}}

[[Category:Thoracic cavity]]