Overview
The thoracic duct is the main and largest lymphatic vessel for the return of chyle/lymph to the systemic venous system. It drains lymph from both lower limbs, abdomen, left hemithorax, left upper limb, left face and neck.
Origin
Superior continuation of the cisterna chyli, a lymph sac at the level of the L1-L2 vertebral body (range T10 – L3)
- To the right side of and posterior to the aorta, adjacent to the right crus of the diaphragm
Course
- Enters the thoracic cavity through the aortic hiatus of the diaphragm and ascends to the right of the midline in the posterior mediastinum between the aorta and azygous vein, posterior to the oesophagus
- It crosses to the left of midline at the thoracic plane (range T4-T6 vertebral body) and continues superiorly through the thoracic inlet, posterior to the left subclavian artery and to the left of the oesophagus
- In the superior mediastinum, it passes posterior the left common carotid artery, the vagus nerve, and the internal jugular vein.
- It continues in the neck anterior to the anterior scalene muscle and phrenic nerve and at the root of the neck, it arches forwards and to the left, behind the carotid sheath and its contents.
- It crosses over the dome of the pleura and left subclavian artery to drain into the junction of the left subclavian and internal jugular veins as a single trunk
Termination
Junction of the left subclavian vein and internal jugular vein
- Thoracic duct may be more often flared or dilated at it terminal end
- There are a pair of valves near its termination which prevent passage of venous blood into the duct
Tributaries
- Posterior intercostal nodes – receives lymph from the glands of the lower 6 or 7 intercostal spaces bilaterally. This then drains into the right and left descending thoracic lymph trunks which open near the origin of the thoracic duct on either side
- Upper left intercostal lymph trunk – drains the left upper 5 intercostal spaces which then drain into the more distal, left side of the thoracic duct
- Posterior mediastinal lymph node efferents
- The thoracic duct also receives right and left trunks that drains the upper lumbar lymph glands, near its origin
- Left jugular lymph trunk – drains left side of head and neck
- Left subclavian lymph trunk – drains left axilla and upper limb
- Left bronchomediastinal trunk – drains left lung and heart
Relations
- Anterior: oesophagus, left atrium, carina
- Posterior: vertebral column, terminal hemiazygous and accessory hemiazygous veins, right posterior intercostal arteries
- Left lateral: descending aorta, left lung and pleura
- Right lateral: azygous vein, right lung and pleura
Development
- The thoracic duct develops from lymphatic trunks on either side of the aorta that anastomoses to form a channel from the jugular lymph sacs to the cisterna chyli.
- Trunks continue to anastomose and enlarge, forming embryonic right and left thoracic ducts.
- The adult thoracic duct is derived from both of these embryonic thoracic ducts.
- The right primitive thoracic duct eventually develops into the lower adult thoracic duct whereas the left primitive thoracic duct develops into the upper portion of the adult thoracic duct.
Anatomical Variants
- Variable level of cistern chyli (ranges from T10 – L3)
- Double thoracic ducts (i.e. multiple ducts) (~20%)
- Aberrant termination: left internal jugular vein, left external jugular vein, azygos vein, brachiocephalic vein or left subclavian vein
- Multiple terminal channels from a single duct with a typical course (~20%)
- Continues on the right to terminate in the right internal jugular vein