3.1 Mediastinum

• The mediastinum is divisible into superior and inferior divisions by an imaginary plane passing from angle of Louie anteriorly and lower border of T4 posteriorly.
• Divisions of the mediastinum


  • Superior
  • Inferior
• Boundaries of the mediastinum

  • Superior - root of the neck, thoracic inlet
  • Inferior - diaphragm
  • Anterior - sternum & costal cartilages; xiphisternal joint at level of 9th thoracic vertebra
  • Posterior - bodies of the 12 thoracic vertebra
• A patient has a small but solid tumor in the mediastinum which is confined at the level of the sternal angle. The beginning of the Ascending aorta would most likely be found at this level.
• CONTENTS OF THE MEDIASTINUM
• Contents of the Superior Mediastinum

  • Superior Vena Cava
  • Brachiocephalic veins
  • Arch of Aorta
  • Thoracic duct
  • Trachea
  • Esophagus
  • Vagus Nerve
  • Left Recurrent LN
  • Phrenic Nerve
  • Thymus gland
  • Lymph nodes
  • Sympathetic trunks
• Contents of the Anterior Mediastinum

  • Remnants of Thymus gland
  • Lymph nodes
  • Fats
• Thymus gland is located in the Anterior mediastinum; attains its greatest size in neonates and children at which time it may EXTEND up through the Superior mediastinum after which it involutes and thymic remnants replaced by fats
• Boundaries of the Anterior Mediastinum


  • Superior: horizontal plane
  • Inferior: Diaphragm
  • Anterior: body and xiphoid process of sternum
  • Posterior: heart
  • Lateral: lungs and pleura
• Contents of the Anterior Mediastinum

  • Thymus gland
  • Anterior group of mediastinal lymph nodes
  • Internal mammary vessels
• Contents of the Middle Mediastinum

  • Heart enclosed in pericardium
  • Arteries: Ascending aorta, Pumonaru trunk with its left and right branches
  • Veins: SVC, Termination of Azygos, Pulmonary veins
  • Nerves: Phrenic, deep cardiac plexus
  • Birfurcation of trachea with two principal bronchi
• Contents of the Posterior Mediastinum

  • Esophagus
  • Vagus nerves around esophagus
  • Thoracic duct: posterior to esophagus
  • Descending aorta: posterior and to the left of esophagus
  • Right and left sympathetic trunks
  • Lymph nodes
• A cross sectional image of the thorax reveals an absence of an anterior mediastinum shadow in a patient diagnosed with DiGeorge syndrome. The thymus and parathyroid glands would be absent in this patient.
• Thymus gland


  Bilobed structure, attains its greatest size in the neonate, playing a key role in the development of the immune system in early life but continues to grow until puberty and then it undergoes gradual involution in which the thymic tissue is replaced by fat
• A patient was admitted to the hospital because of a stab wound on the chest just left to the sternum. The needle must traverse the fibrous pericardium to reach the accumulating blood in the pericardial cavity.