Mediastinum


The mediastinum from Medieval Latin mediastinus, "midway"1 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, trachea, phrenic and cardiac nerves, the thoracic duct, thymus and lymph nodes of the central chest

Contents

  • 1 Structure
    • 11 Superior mediastinum
    • 12 Thoracic plane
    • 13 Inferior mediastinum
  • 2 Clinical significance
    • 21 Widened mediastinum
  • 3 See also
  • 4 References
  • 5 External links

Structureedit

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–T5234
  • 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 anterior mediastinum5page needed

Superior mediastinumedit

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

Thoracic planeedit

  • 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–T5678

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

Structures at the level of the thoracic plane edit
  1. The start and end of the aortic arch
  2. The division between the superior and inferior mediastinum
  3. The upper margin of the superior vena cava 9
  4. The crossing of the thoracic duct
  5. The bifurcation of the trachea 10
  6. The bifurcation of the pulmonary trunk
  7. The level of the sternal angle
  8. The level of Rib 2 where it attaches to the sternum via the 2nd costal cartilage
  9. The body of vertebrae T4 the disc between the vertebrae T4 and T5
  10. The drainage of the azygos vein into the superior vena cava
  11. thymus glandin some cases

compiled by

Inferior mediastinumedit

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

Clinical significanceedit

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's syndrome, or spontaneous esophageal rupture

Widened mediastinumedit

Widened mediastinum
Synonyms Mediastinal widening
Widened mediastinum in a patient with achalasia
Classification and external resources
ICD-9-CM 5193
DiseasesDB 29459
edit on Wikidata

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:1213

  • aortic aneurysm14
  • aortic dissection15
  • 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 200116
  • esophageal rupture - presents usually with pneumomediastinum and pleural effusion It is diagnosed with water-soluble swallowed contrast
  • mediastinal mass
  • mediastinitis
  • cardiac tamponade17
  • pericardial effusion
  • thoracic vertebrae fractures in trauma patients

See alsoedit

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

Referencesedit

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

  1. ^ Mediastinum dictionary definition
  2. ^ Thoracic Wall, Pleura, and Pericardium - Dissector Answers
  3. ^ Untitled Document
  4. ^ UAMS Department of Anatomy - Topographical Anatomy - Thorax
  5. ^ Goodman, Lawrence Felson's Principles of Chest Roentgenology 
  6. ^ Thoracic Wall, Pleura, and Pericardium - Dissector Answers
  7. ^ Untitled Document
  8. ^ UAMS Department of Anatomy - Topographical Anatomy - Thorax
  9. ^ Arai et al Radiographic landmarks of the upper margin of the superior vena cava SVC in children Canadian Journal of Anesthesia 49 Supplement 1: 32
  10. ^ Viscera of the Thorax UAMS Department of Anatomy
  11. ^ D'Souza, Donna "Thoracic aortic injury | Radiology Reference Article | Radiopaediaorg" radiopaediaorg 
  12. ^ Geusens; Pans, S; Prinsloo, J; Fourneau, I 2005 "The widened mediastinum in trauma patients" European journal of emergency medicine 12 4: 179–184 PMID 16034263 doi:101097/00063110-200508000-00006 
  13. ^ 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 PMC 1358125  PMID 2357135 doi:101097/00000658-199006000-00012 
  14. ^ Chandra S, Laor YG April 1975 "Lung scan and wide mediastinum" J Nucl Med 16 4: 324–5 PMID 1113190 
  15. ^ 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 PMID 14715319 doi:101016/jamjmed200308030 
  16. ^ 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 PMC 2631903  PMID 11747719 doi:103201/eid0706010604 
  17. ^ 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 linksedit

  • 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"


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