Thoracic Duct: Anatomy, Function, and Lymphatic Drainage

Overview

The thoracic duct is the largest lymphatic vessel, draining ~75% of the body's lymph.

Course and Relations

• Origin: Cisterna chyli (retroperitoneal, at L1–L2), receiving intestinal trunk and bilateral lumbar trunks.
• Ascends: Posterior to the aorta, through the aortic hiatus of the diaphragm into the thorax.
• In thorax: Runs behind the esophagus, between azygos vein and aorta.
• Termination: Empties into the venous system at the junction of the left internal jugular and left subclavian veins (left venous angle).

Drainage Territory

All body regions below the diaphragm + left upper limb, left hemithorax, left side of head/neck. Excludes: right upper limb, right hemithorax, right side of head/neck (drained by right lymphatic duct).

Key Functions

• Returns filtered plasma proteins and excess interstitial fluid to bloodstream.
• Transports dietary lipids (as chyle) from intestinal lacteals via intestinal trunk → thoracic duct → blood.
• Lymph nodes along its course filter pathogens and debris.

Clinical Relevance

• Chylothorax: Trauma or malignancy disrupts duct → chyle accumulates in pleural space.
• Thoracic duct ligation/embolization treats refractory chylothorax.
• Virchow's node (left supraclavicular) receives drainage via thoracic duct; enlargement signals abdominal malignancy.