Mediastinum

Mediastinum

Mediastinum. The division between superior and inferior is at the sternal angle.

Mediastinum anatomy
Identifiers
Gray's p.1090
Dorlands
/Elsevier		 m_06/12518945
TA A07.1.02.101
FMA 9826
Anatomical terminology

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.

Structure

The mediastinum lies between the right and left pleurae in and near the median sagittal plane of the chest. It extends from the sternum in front to the vertebral column behind, and contains all the thoracic organs except the lungs. It may be divided for purposes of description into two parts: an upper or superior part and a lower or inferior part.

The superior mediastinum extends from the upper level of the pericardium with its upper limit at the superior thoracic aperture and its lower limit at the thoracic plane which runs from the sternal angle (the joint between the manubrium and the body of the sternum) to the intervertebral disc of T4-T5. [2][3][4]The (transverse) thoracic plane divides the mediastinum into these upper and lower parts. The inferior mediastinum extends below the upper level of the pericardium onto the diaphragm. This lower part is subdivided into three regions all relative to the pericardium. The anterior mediastinum is in front of the pericardium. The middle mediastinum contains the pericardium and its contents. The posterior mediastinum is behind the pericardium.

It is surrounded by the chest wall in front, the lungs to the sides and the spine at the back. It is continuous with the loose connective tissue of the neck.

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 mediastinum.[5]

Significant findings at the level of the thoracic plane

1. The start and end of the aortic arch

2. The upper margin of the superior vena cava [6]

3. The crossing of the thoracic duct

4. The bifurcation of the trachea [7]

5. The bifurcation of the pulmonary trunk

6. The level of the sternal angle (angle of Louis)

7. The level of Rib 2 where it attaches to the sternum via the 2nd costal cartilage

8. The body of vertebrae T4

9. The drainage of the azygos vein into the superior vena cava

Contents

Anterior mediastinum

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
Posterior mediastinum

It is bounded:

  • anteriorly by the pericardium (in front of)
  • inferiorly by the thoracic surface of the diaphragm (below).
  • superiorly by the transverse thoracic plane (above). This plane is marked by an imaginary line travelling through the manubriosternal joint to the dividing line between the fourth and fifth thoracic vertebrae.
  • posteriorally 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
Middle mediastinum

Bounded: pericardial sac

Contents
Superior mediastinum

The superior mediastinum is bounded by:

  • superiorly by the thoracic inlet, the upper opening of the thorax
  • inferiorly by the transverse thoracic plane, a slightly oblique plane passing posteriorly from the junction of the manubrium and body of the sternum (sternal angle of Louis) to the junction of the 4th and 5th thoracic vertebra (see also thoracic plane)
  • laterally by the pleurae
  • anteriorly by the manubrium of the sternum
  • posteriorly by the first four thoracic vertebral bodies
Contents

Clinical significance

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

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.

There are many diseases that can present with a widened mediastinum (usually found via a chest x-ray). The most common ones are aortic unfolding, traumatic aortic rupture, thoracic aortic aneurysm, and traumatic thoracic vertebral fracture. With infectious etiologies, a widened mediastinum is a classic hallmark sign of anthrax infection.

See also

References

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. ↑ RADIOGRAPHIC LANDMARKS OF THE UPPER MARGIN OF THE SUPERIOR VENA CAVA (SVC) IN CHILDREN. - Arai et al. 49 (Supplement 1): 32 - Canadian Journal of Anesthesia
  7. ↑ UAMS Department of Anatomy - Viscera of the Thorax

Additional images

External links

Look up mediastinum in Wiktionary, the free dictionary.