The thoracic duct is the main lymphatic vessel for the return of chyle/lymph to the systemic venous system. It drains lymph from both lower limbs, abdomen (except the convex area of the liver), left hemithorax, left upper limb and left side of face and neck. The right lymphatic duct drains the remaining right hemithorax, right upper limb, right face and neck.
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Gross anatomy
The thoracic duct is the superior continuation of the cisterna chyli at the level of the L1 vertebral body (range T10-L3).
The thoracic duct enters the thoracic cavity through the aortic hiatus and ascends to the right of the midline in the posterior mediastinum between the aorta and azygos vein, posterior to the esophagus.
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. At the root of the neck, it arches forwards and to the left, behind the left carotid sheath 7, before crossing over the dome of the left pleura and left subclavian artery, passing anterior to the anterior scalene muscle and phrenic nerve to drain into the angle of the left subclavian and internal jugular veins as a single trunk 1-4.
In its terminal (distal) portion the thoracic duct may be more often flared or dilated rather than continue at a consistent diameter 1.
Relations
anterior: esophagus, left atrium, carina
posterior: vertebral column, terminal hemiazygos and accessory hemiazygos veins, right posterior intercostal arteries
left lateral: descending aorta, left lung and pleura
right lateral: azygos vein, right lung and pleura
Tributaries
Near its origin (see: cisterna chyli):
ascending lumbar, intestinal, liver and descending intercostal lymph trunks
In the thorax:
the lower 6 or 7 intercostal spaces are drained by the posterior intercostal lymph nodes which then drain 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 is responsible for draining the left upper 5 intercostal spaces which then drain into the more distal, left side of the thoracic duct
Near its termination:
left jugular lymph trunk (draining left side of head and neck)
left subclavian lymph trunk (draining left axilla and upper limb)
left bronchomediastinal trunk (draining left lung and heart)
Variant anatomy
The thoracic duct has variant anatomy in ~40% (range 30-50%) of the population 1, 4:
double thoracic ducts (i.e. multiple ducts) (~20%) 1,2,4
aberrant termination: left internal jugular vein, left external jugular vein, azygos vein, brachiocephalic vein or left subclavian vein 1,4
multiple terminal channels from a single duct with a typical course (~20%) 4
continues on the right to terminate in the right internal jugular vein 5
Related pathology
Pathology of the thoracic duct is rare but includes:
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