In human anatomy, the thoracic duct (also known as the left lymphatic duct, alimentary duct, chyliferous duct, and Van Hoorne's duct) is the larger of the two lymph ducts of the lymphatic system (the other being the right lymphatic duct). The thoracic duct usually begins from the upper aspect of the cisterna chyli, passing out of the abdomen through the aortic hiatus into first the posterior mediastinum and then the superior mediastinum, extending as high up as the root of the neck before descending to drain into the systemic (blood) circulation at the venous angle.
The thoracic duct carries chyle, a liquid containing both lymph and emulsified fats, rather than pure lymph. It also collects most of the lymph in the body other than from the right thorax, arm, head, and neck (which are drained by the right lymphatic duct).
Origin
The thoracic duct commences at the upper extremity of the cisterna chyli at the level of the T12 vertebra. and is situated posterior to the esophagus at the T7 vertebral level. It crosses the midline to the left side at about the T5 level, continuing to ascend. It then passes posterior to the aorta, and to the left of the oesophagus.
In the superior mediastinum, the thoracic duct is situated posterior to and to the left of the esophagus. It is situated between the visceral and alar fascia. These are drained by the right lymphatic duct.
Clinical significance
The thoracic duct becomes adaptively dilated in the presence of certain pathological conditions (congestive heart failure, portal hypertension, and malignancy).