Thoracic duct

Ductus thoracicus

Also known as: left lymphatic duct, alimentary duct, van Hoorne canal

The largest lymphatic vessel (≈ 38–45 cm): it rises from the cisterna chyli through the aortic hiatus and posterior mediastinum to empty into the left venous angle, draining about three-quarters of the body.

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Overview

Length≈ 38–45 cm

Diameter≈ 2–5 mm (wider at the cisterna)

Flow≈ 100 mL/h at rest (≈ 1.5–2.5 L/day)

Crosses midlineT4–T5 (sternal angle), right → left

The thoracic duct drains lymph from the entire body except the right upper quadrant — i.e. both lower limbs, pelvis, abdomen, the left thorax, left upper limb and left side of the head and neck. Beginning at the cisterna chyli (≈ L1–L2), it ascends through the aortic hiatus of the diaphragm at T12 with the aorta and azygos vein. In the posterior mediastinum it lies on the vertebral bodies between the descending thoracic aorta (left) and the azygos vein (right), behind the oesophagus. At about T4–T5 (sternal angle) it crosses obliquely to the left, behind the oesophagus, and ascends in the superior mediastinum along the left edge of the oesophagus, behind the left subclavian artery.

At the root of the neck (≈ C7) it arches laterally over the dome of the pleura, passing anterior to the vertebral artery and vein, the sympathetic trunk and the thyrocervical trunk, and behind the left carotid sheath, to empty into the left venous angle (junction of the left internal jugular and left subclavian veins). Near its termination it usually receives the left jugular, subclavian and bronchomediastinal trunks. It is beaded, with numerous valves; a valve at its termination prevents blood entering the duct.

The duct carries ≈ 1.5–2.5 L of lymph per day; after a fatty meal this is milky chyle. Duplications, plexiform segments and right-sided termination (≈ 1–5%) are common variants, reflecting its origin from paired embryonic ducts.

Location: Posterior abdominal wall (L1–L2) → posterior mediastinum → superior mediastinum → root of the neck (left).

Parts & subdivisions

Abdominal part
Origin at the cisterna chyli (L1–L2); passes through the aortic hiatus at T12.
Thoracic part (posterior mediastinum)
Between the aorta and azygos vein, behind the oesophagus; crosses to the left at T4–T5.
Thoracic part (superior mediastinum)
Ascends on the left of the oesophagus, behind the left subclavian artery and medial to the left pleura.
Cervical part
Arches at C7 level over the pleural dome and in front of the vertebral artery to end at the left venous angle.

Anatomy

Course: Cisterna chyli (L1–L2) → aortic hiatus (T12) → posterior mediastinum between aorta and azygos vein, behind the oesophagus → crosses right-to-left at T4–T5 → superior mediastinum to left of oesophagus → arches at C7 anterior to the vertebral artery and posterior to the carotid sheath → left venous angle.
Tributaries: Cisterna chyli (lumbar and intestinal trunks); descending intercostal trunks; vessels from posterior mediastinal nodes; upper intercostal efferents; left bronchomediastinal, left subclavian and left jugular trunks (or these open independently).
Relations: Posterior mediastinum: anterior — oesophagus (and diaphragm below); posterior — vertebral bodies, right posterior intercostal arteries, hemiazygos veins; left — descending aorta; right — azygos vein. Neck: posterior to left common carotid artery, vagus nerve and internal jugular vein; anterior to vertebral artery, sympathetic trunk, thyrocervical trunk, phrenic nerve (on scalenus anterior).

Function

Returns lymph from ≈ ¾ of the body to the venous blood.
Delivers absorbed dietary fat (chylomicrons) to the systemic circulation, bypassing the liver.
Returns recirculating lymphocytes to the blood.

Clinical significance

Chylothorax

Injury during oesophagectomy, cardiothoracic or spinal surgery, trauma or malignant obstruction (lymphoma) leaks chyle into the pleura. Because of the crossing at T4–T5, damage below this level typically causes a right chylothorax and damage above it a left chylothorax. A milky effusion with high triglycerides is diagnostic.

Virchow node

Tumour cells travelling up the duct from abdominal or pelvic cancers (especially stomach) may lodge in the left supraclavicular nodes near its termination — Troisier sign.

Surgical injury in the neck

Left-sided neck dissection or central line insertion can damage the duct, causing a cervical chyle fistula.

Mnemonics

Position in the posterior mediastinum

"The duck between two gooses" — the thoracic duct lies between the az-ygos vein and the a-orta.

Test yourself

Where does the thoracic duct normally terminate?

Junction of the right internal jugular and right subclavian veins
Junction of the left internal jugular and left subclavian veins
Superior vena cava, just above the azygos vein
Left brachiocephalic vein near the manubrium

Answer: Junction of the left internal jugular and left subclavian veins

The thoracic duct arches over the left subclavian artery at the root of the neck (≈ C7) and empties into the left venous angle, where the left internal jugular and left subclavian veins unite. The right lymphatic duct uses the right venous angle.

Lymph from which region does NOT normally enter the thoracic duct?

Left lower limb
Small intestine
Right upper limb
Left side of the head and neck

Answer: Right upper limb

The thoracic duct drains everything below the diaphragm plus the left side above it. The right upper limb, right head and neck and right thorax drain via the right jugular, subclavian and bronchomediastinal trunks to the right lymphatic duct.

More lymphatic & immune system questions

Compiled from standard anatomy and physiology references — see the Lymphatic & Immune System sources. For education only; not medical advice.