Superior Mediastinum and Root of Neck - LO 6

6. Differentiate between the superior, anterior, middle, and posterior mediastinal spaces.

The mediastinum may be classically described as four contiguous spaces, or (more recently) clinically described as three contiguous compartments. Both classifications may be encountered, but anatomists typically use the four-space model. 

The mediastinum is the region bounded:

• • Superiorly by the thoracic inlet (and first ribs),

  • Inferiorly by the diaphragm,

  • Laterally by the pleura,

  • Anteriorly by the sternum and pleurae, &

  • Posteriorly by the vertebral column.

Classically, the mediastinum may be subdivided into four regions: superior, anterior, middle, and posterior mediastina. 

The superior mediastinum is distinguished from all other regions by the plane of the sternal angle, i.e. a transverse plane running from the sternal angle (where the manubrium meets the body of the sternum; a landmark for locating the level of the 2nd costal cartilage) to the T4/5 intervertebral disc.

The anterior mediastinum is delimited as the space:

• • Inferior to the plane of the sternal angle,

  • Superior to the diaphragm,

  • Posterior to the sternum and thoracic wall,

  • Anterior to the pericardium, &

  • Medial to the pleurae.

The posterior mediastinum is the area:

• • Inferior to the plane of the sternal angle,

  • Superior to the diaphragm,

  • Posterior to the pericardium,

  • Anterior to the vertebral column, &

  • Medial to the pleurae.

The middle mediastinum is the area:

• • Inferior to the plane of the sternal angle,

  • Superior to the diaphragm,

  • Posterior to the anterior-most extent of the pericardium, 

  • Anterior to the posterior-most extent of the pericardium, &

  • Medial to the pleurae.

The mediastinum may also be described as three compartments: the prevascular, visceral, and paravertebral compartments. As with the four-regions model, the pericardium is a pivotal element for delimiting the compartments, with prevascular anterior to the pericardium, the visceral compartment bounded by the pericardium, and the paravertebral compartment posterior to the pericardium.

The prevascular compartment is bounded:

• • Superiorly by the thoracic inlet and first ribs,

  • Inferiorly by the diaphragm,

  • Anteriorly by the sternum,

  • Posteriorly by the anterior-most extent of the pericardium, &

  • Laterally by the pleurae.

The visceral compartment is bounded:

• • Superiorly by the thoracic inlet and first ribs,

  • Inferiorly by the diaphragm,

  • Anteriorly by the anterior-most extent of the pericardium,

  • Posteriorly by the a line including the anterior 1 cm of each thoracic vertebra, & 

  • Laterally by the pleurae.

The paravertebral compartment is bounded:

• • Superiorly by the thoracic inlet and first ribs,

  • Inferiorly by the diaphragm,

  • Anteriorly by a line including the anterior 1 cm of each thoracic vertebra,

  • Posteriorly by the area adjacent to the thoracic vertebral bodies, &

  • Laterally by the pleurae.