Mediastinum encyclopedia topics

Anatomy

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 opening and its inferior limit at the plane from the sternal angle to the disc of T4-T5 (Plane of Ludwig);
and a lower portion, below the upper level of the pericardium. This lower portion is again 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.

Note that clinical radiologists and anatomists categorize the mediastinum in slightly different ways.

Role in disease

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 two conditions frequently accompany Boerhaave's syndrome, or spontaneous esophageal rupture.

A widened mediastinum (usually found via a chest x-ray) is a classic hallmark sign of anthrax poisoning. At this point, the disease is typically fatal.