The mediastinum is a central partition between the two laterally located pleural cavities. It extends from the superior thoracic aperture to the inferior thoracic aperture and diaphragm, and between the sternum anteriorly and the bodies of the thoracic vertebrae posteriorly.
For organizational purposes, the mediastinum is subdivided in smaller sections. A horizontal plane (transverse thoracic plane) passing through the sternal angle to the intervertebral disc between the 4th and 5th thoracic vertebrae divides mediastinum into two compartments:
- Superior mediastinum - between the superior thoracic aperture and the transverse thoracic plane;
- Inferior mediastinum - between the transverse thoracic plane and the diaphragm. The inferior mediastinum is larger and can be further subdivided into three parts - anterior, middle and posterior mediastinum.
Every compartment of the mediastinum contains vital organs, vascular and neural structures that are closely related to one another.