Thoracic Duct

Thoracic Duct

• The thoracic duct is the largest lymphatic vessel in the body.
• Length: approximately 45 cm
• Width: about 5 mm
• It extends from the upper abdomen to the lower part of the neck.
• Numerous valves along its course give the duct a characteristic beaded appearance.

Beginning

The thoracic duct begins as the upward continuation of the cisterna chyli at the level of the lower border of T12 vertebra.

Course

• It enters the thoracic cavity through the aortic opening of the diaphragm at the T12 vertebral level.
• The duct ascends through the posterior mediastinum, initially on the right side.
• At approximately the T5 vertebral level, it crosses from right to left.
• It then continues upward through the superior mediastinum along the left side of the esophagus.
• At the root of the neck, the duct arches laterally at the level of the C7 transverse process, approximately 3–4 cm above the left clavicle.

Termination

• The thoracic duct terminates at the left jugulosubclavian angle, formed by the junction of the left internal jugular vein and left subclavian vein.

Relations

At aortic opening

• Anterior: Diaphragm, including the median arcuate ligament
• Posterior: T12 vertebra
• Right: Azygos vein
• Left: Aorta

In the posterior mediastinum

• Anterior:

• Diaphragm
• Esophagus
• Posterior:
  • Vertebral column
  • Right posterior intercostal arteries
  • Terminal portions of the hemiazygos and accessory hemiazygos veins
• Right: Azygos vein
• Left: Descending thoracic aorta

In the superior mediastinum

• Anterior:
  • Arch of the aorta
  • Origin of the left subclavian artery
• Posterior: Vertebral column
• Right: Esophagus
• Left: Left lung and pleura

In the root of the neck

• Anterior: Left carotid sheath
• Posterior:
  • Left sympathetic trunk
  • Inferior cervical ganglion
  • Vertebral artery and vein
  • Thyrocervical trunk and its branches
  • Left phrenic nerve
  • Medial border of scalenus anterior muscle

Tributaries

In the Abdomen

• The thoracic duct begins as the upward continuation of the cisterna chyli.

In the Thorax

• A pair of descending lymphatic trunks draining the posterior intercostal lymph nodes of the lower six intercostal spaces
• A pair of ascending lymphatic trunks draining the upper lumbar lymph nodes
• Lymphatic vessels from the posterior mediastinal lymph nodes

In the Neck

• Left jugular lymph trunk: Drains lymph from the left half of the head and neck.
• Left subclavian lymph trunk: Drains the left upper limb.
• Left bronchomediastinal lymph trunk: Drains the left lung and the left side of the heart.

Area of Drainage

• The thoracic duct drains lymph from most of the body.
• It does not drain the right upper quadrant, which includes:

• Right side of the head and neck
• Right upper limb
• Right side of the thoracic wall
• Right lung
• Right side of the heart
• Right surface of the liver

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