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

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