Mediastinum

 

Mediastinum is the middle space left in the thoracic cavity in between the two lungs.

Division:-

 • the mediastinum is divided into the superior mediastinum and the inferior mediastinum.

 • The inferior mediastinum is further divided in to the anterior, middle and posterior mediastina.

Posterior Mediastinum :-

Boundaries:-

 1. Anteriorly

 • Pericardium

 • bifurcation of trachea

 • pulmonary vessels,

 • posterior part of the upper surface of the diaphragm.

 2. Posteriorly

 • Lower eight thoracic vertebrae and intervening discs.

 3. On each side

 • Mediastinal pleura.

Contents:-

 1. Oesophagus

 2. Arteries

 • Descending thoracic aorta and its branches.

 3. Veins

 • Azygos vein,

 • hemiazygos vein

 • accessory hemiazygos vein

 4. Nerves

 • Vagi

 • splanchnic nerves, greater, lesser and least, a rising from the lower eight thoracic ganglia of the sympathetic chain

 5. Lymph nodes and lymphatics:

 • Posterior mediastinal lymph nodes

 • The thoracic duct

SUPERIOR MEDIASTINUM :-

Boundaries:-

 1. Anteriorly:- Manubrium sterni

 2. Posteriorly :- Upper four thoracic vertebrae

 3. Superiorly :- Plane of the thoracic inlet

 4. Inferiorly :- An imaginary plane passing through the sternal angle in front, and the lower border of the fourth thoracic vertebra behind.

 5. On each side: Mediastinal pleura.

Contents:-

 1. Trachea and oesophagus.

 2. Muscles:- Origins of

 • sternohyoid

 • sterno-thyroid

 • lower ends of longus colli

 3. Arteries

 • Arch of aorta

 • brachiocephalic artery

 • left common carotid artery

 • left subclavian artery

 4. Veins

 • Right and left brachiocephalic veins

 • upper half of the superior vena cava

 • left superior intercostal vein.

 5. Nerves

 • Vagus

 • phrenic

 • cardiac nerves of both sides

 • left recurrent laryngeal nerve.

 6. Thymus

 7. Thoracic duct

 8. Lymph nodes

 • Paratracheal

 • brachiocephalic and

 • tracheobronchial

Clinical anatomy:-

In the superior mediastinum,

 all large veins are on the right side and

 the arteries on the left side.

During increased blood flow, veins expand enormously, while the large arteries do not expand at all. Thus there is much 'dead space' on the right side and it is into this space that tumour or fluids of the mediastinum tend to project.