Lecture Notes: The Mediastinum

Introduction

• Presenter: Dr. Morton, a noted anatomist.
• Topic: Understanding the Mediastinum and its regional anatomy.

Definition and Location

• Mediastinum: Means "Midway"; located midway between the lungs, sternum, and vertebrae in the thoracic cavity.
• Regions of the Mediastinum:
  • Superior Mediastinum: Between the first rib and the transverse thoracic plane.
  • Inferior Mediastinum: Between the transverse thoracic plane and the diaphragm.
    • Further divided into:
      • Anterior Mediastinum: Contains the thymus.
      • Middle Mediastinum: Contains the pericardial sac and heart.
      • Posterior Mediastinum: Behind the heart; focus of the lecture.

Posterior Mediastinum

• Analogy: Compared to the area behind a living room TV, filled with organized structures.
• KEY ACRONYM: DATES
  • Descending aorta
  • Azygos system of veins
  • Thoracic duct
  • Esophagus
  • Sympathetics

Descending Aorta

• Originates from the aortic arch.
• Supplies posterior intercostal arteries at each segment.
• Pierces diaphragm at T12 vertebral level.

Azygos System of Veins

• Drains venous blood from the posterior abdominal and thoracic walls.
• Components:
  • Azygos vein: Drains right side into superior vena cava (SVC).
  • Accessory Hemiazygos vein: Drains upper left thoracic.
  • Hemiazygos vein: Drains lower left thoracic and abdominal regions.

Thoracic Duct

• Largest lymphatic vessel, transporting ~4 liters of lymph/day.
• Originates from cisterna chyli.
• Drains into systemic circulation at the junction of left internal jugular and subclavian veins.

Esophagus

• Transports food from pharynx to stomach.
• Passes through diaphragm at esophageal hiatus (T10 level).
• Innervated by the vagus nerve forming an esophageal plexus.

Sympathetics

• Sympathetic Trunk: Chain of sympathetic ganglia along vertebral column.
• Splanchnic Nerves:
  • Greater Splanchnic Nerve: T5-T9
  • Lesser Splanchnic Nerve: T10-T11
  • Least Splanchnic Nerve: T12

Superior Mediastinum

• Located between the first rib and the transverse thoracic plane.
• Planes:
  • Venous Plane: Includes jugular veins, subclavian veins, and superior vena cava (SVC).
  • Arterial Plane: Aortic arch and its branches (brachiocephalic trunk, left common carotid, and left subclavian arteries).
  • Visceral Plane: Contains the trachea and esophagus.

Key Takeaway

• The mediastinum encompasses critical anatomical regions and structures vital for cardiovascular, lymphatic, and respiratory systems.
• Focus is on understanding the arrangement and function of structures in the posterior and superior mediastina.