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
Gray's p.1090

The mediastinum 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 pleura 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 viscera except the lungs. It may be divided for purposes of description into two parts:

  • an upper portion, above the upper level of the pericardium, which is named the superior mediastinum with its superior limit at the superior thoracic aperture and its inferior limit at the plane from the sternal angle to the disc of T4-T5 (Plane of Ludwig at Angle of Louis);
  • and a lower portion, below the upper level of the pericardium. This lower portion is subdivided into three parts, viz.:
    • that in front of the pericardium, the anterior mediastinum;
    • that containing the pericardium and its contents, the middle mediastinum;
    • and that behind the pericardium, the posterior mediastinum.

It is surrounded by the chest wall anteriorly, the lungs laterally and the spine posteriorly. It is continuous with the loose connective tissue of the neck, and extends inferiorly onto the diaphragm.

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.[1][page needed]

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.

  1. ^ Goodman, Lawrence. Felson's Principles of Chest Roentgenology. 

Additional images[edit]

External links[edit]