The mediastinum is the central compartment of the thoracic cavity, located between the two pleural sacs. It contains most of the thoracic organs and serves as a conduit for structures traversing the thorax to the abdomen. Anatomically, it is divided by an imaginary line from the sternal angle to the T4 vertebra into:

• Superior mediastinum – extending upwards to the thoracic inlet
• Inferior mediastinum – extending downward to the diaphragm, further divided into
  • Anterior
  • Middle
  • Posterior mediastinum

This section focuses on the posterior mediastinum—its borders, contents, and key anatomical relations.

Borders of the Posterior Mediastinum

Contents of the Posterior Mediastinum

1. Thoracic Aorta
   • Continuation of the arch of the aorta, beginning at T4 and ending at T12, where it becomes the abdominal aorta.
   • Gives off several branches:
     • Posterior intercostal arteries (9 pairs)
     • Bronchial arteries (1–2 branches)
     • Oesophageal arteries (2–5 branches)
     • Superior phrenic arteries
2. Oesophagus
   • A muscular tube connecting the pharynx to the stomach, descending posterior to the heart.
   • Deviates slightly left as it descends and exits through the oesophageal hiatus of the diaphragm.
   • Surrounded by the oesophageal plexus formed by branches of the vagus nerves, forming anterior and posterior vagal trunks.
3. Thoracic Duct
   • The largest lymphatic vessel in the body originates from the cisterna chyli.
   • Ascends anterior to T6–T12 vertebrae and carries lymph from most of the body into the venous system.
4. Azygos System of Veins
   1. Drains blood from the thoracic wall into the superior vena cava.
   2.  Includes:
      1. Azygos vein (right side)
      2. Hemiazygos vein (left lower)
      3. Accessory hemiazygos vein (left upper)
5. Sympathetic Trunks
   1. Paired nerve chains extending from the base of the skull to the coccyx.
   2. In the thoracic region, they give rise to thoracic splanchnic nerves, which supply the abdominal viscera.

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