The Mediastinum

This is the region of the thoracic cavity between the two pleural cavities. It is what is left after the lungs and the pleura have been removed from the thoracic cavity.

   

Extents and boundaries

 

 

  • The mediastinum (a) extends from the superior thoracic inlet superiorly, to the thoracic diaphragm inferiorly .

  • Boundaries
Anteriorly Sternum and costal cartilages
Posteriorly

Thoracic vertebrae and their associated intervertebral discs and anterior longitudinal ligaments.
Laterally pleural cavities, containing the lungs.
   
  • The root of the lungs connects the mediastinum to the lungs.
Sub-divisions of mediastinum  

The mediastinum is divided by a plane passing from the sternal angle to T4-T5 into:

  • Superior mediastinum (1) and
  • The inferior mediastinum (2,3.4)

The inferior mediastinum is further subdivided into three regions namely:

  • Anterior mediastinum
  • Middle mediastinum
  • Posterior mediastinum

These divisions are for descriptive purposes, merge into each other inpercleptibly. There are no distinct boundaries between them.
 
Contents of Superior Mediastinum
Thymus
 

 

    • In the neonate its very large extending from the thyroid gland to the pericardium.

    • Grows slightly until puberty then regresses

    • Plays an important role in regulating the body’s immunity

    • In the adult it is pinkish/ yellowish elongated body consisting of asymmetrical right and left lobes connected by areolar tissue

    • Enclosed in a fibrous capsule