Origin and entry into the thoracic cavity
The thoracic duct (ductus thoracicus) originates deep within the retroperitoneal space. Anatomically, this formation process occurs at the level of the second lumbar vertebra. It is at this level that two large collectors of the lymphatic system—the right and left lumbar trunks (trunci lumbales)—merge.
Following its formation, this slightly tortuous, thin-walled tube directs upwards. To enter the thoracic cavity, the duct uses a natural anatomical aperture—the aortic hiatus of the diaphragm. Passing through this canal, the lymphatic trunk is positioned in a strictly defined manner: it is located to the right and somewhat posteriorly to the abdominal aorta, ensuring its protection by the muscular crura of the diaphragm.
Topography and syntopy in the posterior mediastinum
Once in the thoracic cavity, the duct is usually represented by a single main trunk. It ascends almost vertically, lying within the thickness of the prevertebral tissue, which is located between the leaflets of the prevertebral fascia. In this section, the trunk does not run strictly along the center, but is shifted slightly to the right relative to the median line of the body.
It is important to examine in detail the surrounding anatomical structures (syntopy) of the duct in the posterior mediastinum:
- Posteriorly: the right posterior intercostal arteries run behind the duct, and important venous anastomoses connecting the systems of the azygos and hemiazygos veins are located here.
- Anteriorly: the periesophageal fascia directly adjoins the lymphatic trunk.
- To the right: the duct may be completely or only partially covered by the posterior transitional fold of the pleura.
Along the course of the main trunk, especially in its lower section, lymph nodes are localized. Their main task is to collect lymph from the structures and organs located in the posterior mediastinum. It is worth noting that the anatomy of the duct is variable: in some people, accessory lymphatic ducts are encountered (they can be located anteriorly or to the left of the spinal column), which act as collateral pathways for lymph outflow.
Change of direction, course, and termination
Ascending higher, at the level of the fifth-sixth thoracic vertebrae (Th V–VI), which topographically corresponds to the tracheal bifurcation zone, the duct begins its deviation to the left of the midline of the spine.
In its upper section, the lymphatic trunk lies on the anterior surface of the fourth and third thoracic vertebrae (Th IV–III), and then smoothly transitions to the left lateral surface of the second and first thoracic vertebrae (Th II–I). At the same time, its relationship with large blood vessels and the esophagus changes systematically: initially located to the right of the aorta, it then passes behind the aortic arch and esophagus, finally emerging into the left mediastinum.
At the final stage of its path, the duct passes onto the cervical pleura. It characteristically arches over it in a posteroanterior direction, after which it empties into the left venous angle, returning the collected lymph to the bloodstream.
Clinically important relations
Knowledge of the exact syntopy of the thoracic duct is critically important for practicing surgeons operating on the organs of the chest and neck, as damage to this structure leads to severe complications (chylothorax).
- Relation to nerves: Immediately to the left of the mouth of the duct (at the site of its entry into the venous angle) runs the left recurrent laryngeal nerve, which requires careful protection during interventions.
- Relation to the esophagus: In the area located behind the aortic arch, the lymphatic trunk adheres extremely tightly to the posterior surface of the fascial sheath of the esophagus. This creates a high risk of iatrogenic damage to the duct during surgical operations on the esophagus, requiring extreme caution from the surgeon when isolating the organ.
Briefly: answers to topical questions
From the fusion of which lymphatic trunks is the thoracic duct formed?
The thoracic duct is formed as a result of the fusion of the lumbar and intestinal lymphatic trunks.
- Left and right lumbar trunks (trunci lumbales sinister et dexter) — collect lymph from the lower extremities, pelvis, abdominal wall, and spinal cord.
- Intestinal trunk (truncus intestinalis) — an inconstant third root draining lymph from the digestive organs.
What is the syntopy of the thoracic duct in the posterior mediastinum?
In the posterior mediastinum, the thoracic duct is located within the prevertebral tissue, heading upwards in front of the spinal column. Its syntopy includes the following structures:
- Right posterior intercostal arteries — are located posterior to the duct along with venous anastomoses.
- Periesophageal fascia — is located anterior to the duct.
- Posterior transitional fold of the pleura — is located to the right and may partially or completely cover the duct.
- Thoracic aorta — is located to the left, with the duct adjoining its posterior surface on the right side.
Which lymphatic trunks empty into the cervical part of the thoracic duct before its opening?
Before emptying into the left venous angle, lymphatic trunks pour into the cervical part of the thoracic duct.
- Left jugular trunk — is one of the tributaries of the duct in the neck.
- Left subclavian trunk — also empties into the duct before its opening.
Three trunks pour into the upper part of the thoracic duct, but only the two mentioned above are detailed in the materials.
Are there valves in the thoracic duct and where are they located?
Yes, the thoracic duct has a valve apparatus comprising up to 9 valves. The exact location of all valves along the course of the duct is not detailed, but the structure of its opening is known.
- Valve apparatus — there are up to 9 valves located along the course of the vessel.
- Folds of the opening — the site of entry of the thoracic duct is equipped from the inside with two well-developed folds that prevent blood from penetrating into it.
To remember the course of the duct through the diaphragm: it hides behind the aorta (posteriorly and to the right), as if yielding the way to the main blood vessel of the body.
Class and exam questions
Through which opening of the diaphragm does the duct enter the chest cavity?
The duct passes through the aortic hiatus of the diaphragm, being located to the right and posteriorly to the aorta.
Where does the duct deviate to the left of the midline?
The change of direction (deviation to the left) occurs at the level of the V–VI thoracic vertebrae (Th V–VI), which corresponds to the level of the tracheal bifurcation.
Why do esophageal operations pose a danger to the thoracic duct?
Behind the aortic arch, the duct fuses very tightly with the posterior surface of the periesophageal fascia, so during the mobilization of the esophagus, there is a high risk of dissecting the thin wall of the duct.
What else to study on this topic
- Formation of the lumbar trunks (trunci lumbales) in the retroperitoneal space.
- Variant anatomy: accessory lymphatic ducts and collateral outflow.
- Anatomy and topography of the left venous angle.
- Lymph nodes of the posterior mediastinum: pathways of lymph influx.
- Topography of the left recurrent laryngeal nerve at the site of the duct opening.
Master the complete topic in the "Topographic Anatomy" course
This is a summary. The course covers everything tested in classes and exams.
- Complete study guide on the topic "Thoracic duct" and 2,777 more pages of the subject
- Assignments and quizzes after every topic — just like in a colloquium
- AI tutor answers questions on the topic anytime
- 91 video lessons on the subject
Other topics in the section "Topographic Anatomy of the Chest"
Free video lessons: topographic anatomyShort lessons with study notes — no registration required.
Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.