The mediastinum is the central compartment of the thoracic cavity and lies between the two pulmonary cavities.

It’s covered on each side by the mediastinal pleura and contains all thoracic viscera and structures minus the lungs.

The mediastinum is divided into four parts, of which one is superior and three are inferior.

The superior part is bounded superiorly by the thoracic aperture and extends inferiorly to the transverse thoracic plane, which is a horizontal plane that extends from the sternal angle anteriorly and the junction of T4 and T5 posteriorly.

The transverse thoracic plane separates the superior mediastinum from the inferior mediastinum, and is also an important anatomical landmark representing the bifurcation of the trachea and the beginning and end of the arch of the aorta.

The inferior mediastinum lies between the transverse thoracic plane superiorly, and the diaphragm inferiorly.

It’s further subdivided by the pericardium into anterior, middle and posterior parts, with the pericardium and its contents being in the middle part.

So in this video, let’s focus on the superior mediastinum.

From anterior to posterior, it contains the following structures: the thymus, the great vessels, the inferior continuation of the trachea, the inferior continuation of the esophagus, and the thoracic duct and lymphatics trunks.

Now let’s take a closer look at some of these structures one by one.

So, the thymus is located in the inferior part of the neck and in the anterior part of the superior mediastinum.

It is a glandular structure and lies posterior to the manubrium and extends into the anterior mediastinum.

The thymus is a primary lymphoid organ that plays a huge role in helping our immune cells develop before puberty.

After puberty, however, it undergoes gradual involution and is mostly replaced by fat.

Next up, there are the great vessels.

First we have the veins, which include the brachiocephalic veins and the superior vena cava or SVC, as well as the arteries, which include the arch of the aorta and its major branches, the brachiocephalic trunk, left common carotid artery and left subclavian artery.