Thoracic duct

The thoracic duct is the main lymphatic channel for the return of chyle to the venous system. It drains lymph from both lower limbs, abdomen (except the convex area of the liver), left hemithorax, left upper limb and left face and neck. 

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 oesophagus.

It crosses to the left of midline at the thoracic plane (range T4-T6 vertebral body) and continues superiorly through the thoracic inlet, anterior to the subclavian artery, and continues in the neck anterior to the anterior scalene muscle and phrenic nerve. The thoracic duct then passes posteriorly to the carotid sheath 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: oesophagus, 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

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
• The 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
• Posterior mediastinal lymph node efferents
• The thoracic duct also receives right and left trunks that drains the upper lumbar lymph glands, near its origin

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 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:

• chylothorax