Medaistinum

The Mediastinum is the space in thoracic cavity between lungs.

Boundaries of Mediastinum are:

• Posteriorly: thoracic spine
• Anteriorly: sternum and costal cartilages
• Laterally: mediastinal pleura
• Superiorly: thoracic inlet
• Inferiorly: diaphragm

Sub divisions

A transverse plane passing through the sternal angle to the junction of vertebrae T4/T5 separates superior from inferior mediastinum  Or think of uperior mediastinum as above Heart. Space in front of heart is anterior mediastinum. Space behind heart is posterior mediastinum. Region of heart is the middle mediastinum.

• Superior Mediastinum
• Inferior Mediastinum
  • anterior mediastinum
  • middle mediastinum
  • posterior mediastinum

Boundaries

Superior mediastinum:

• anteriorly: the sternum
• posteriorly: the upper thoracic vertebra
• inferiorly: an arbitrary plane passing horizontally and posteriorly from the manubriosternal joint to the junction of T4/T5 vertebrae
• superiorly: thoracic inlet
• laterally: apices of the lungs

Anterior Mediastinum

• Anteriorly by the sternum,
• laterally by the pleuræ
• Posteriorly by the pericardium.

Middle Mediastinum

• Space occupied by Heart 

Posterior Mediastinum

Runs parallel with the vertebral column

• Anteriorly
  • by the pericardium above
  • by the posterior surface of the diaphragm below
• Posteriorly by the vertebral column from the lower border of the fourth to the twelfth thoracic vertebra
• Laterally by the mediastinal pleura

The key structures in each compartment are:

Superior mediastinum

• trachea
• esophagus
• great vessels
  • the arch of the aorta
  • thoracic portions of the left common carotid and the left subclavian arteries;
• Veins
  • the innominate veins and the upper half of the superior vena cava; 
  • the left highest intercostal vein
• thymus
• phrenic and vagus nerves and  left recurrent nerves
•  thoracic duct
• some lymph glands.

Anterior mediastinum

• Residue of Thymus
• Fat 
• Lymph glands

Middle mediastinum

• Heart
• Pericardium
• Ascending Aorta
• Lower half of Superior Vena cava
• Trachea
• Main bronchi
• Lymph nodes
• Pulmonary artery
• Pulmonary veins
• Phrenic nerve

Posterior mediastinum

• Descending aorta
• Esophagus
• Azygous vein
• Hemiazygous veins
• Lymph glands
• Thoracic duct
• Autonomics
• Vagus