Mediastinum

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Mediastinum
Mediastinum.png
Mediastinum. The division between superior and inferior is at the sternal angle.
Mediastinum anatomy.jpg
Mediastinum anatomy
Identifiers
Gray's p.1090
Dorlands
/Elsevier
m_06/12518945
TA A07.1.02.101
FMA FMA:9826
Anatomical terminology

The mediastinum (from Medieval Latin mediastinus, "midway"[1]) is an undelineated group of structures in the thorax, surrounded by loose connective tissue. It is the central compartment of the thoracic cavity. It contains the heart, the great vessels of the heart, the esophagus, the trachea, the phrenic nerve, the cardiac nerve, the thoracic duct, the thymus, and the lymph nodes of the central chest.

Structure[edit]

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][page needed]

Significant findings at the level of the thoracic plane[edit]

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[edit]

Anterior mediastinum

Bounded:

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
Contents
Superior mediastinum

The superior mediastinum is bounded by:

Contents

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 elsewhence (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.

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[edit]

References[edit]

This article incorporates text from a public domain edition of Gray's Anatomy.

Additional images[edit]

External links[edit]