Thoracic Duct

What is the thoracic duct?

Your thoracic duct is the biggest lymphatic vessel in your body. It’s a long, tubelike structure that carries lymph from your belly area up through your chest. Like a highway on-ramp, your thoracic duct merges into large veins near the base of your neck. This allows lymph to rejoin your bloodstream and continue its journey through your body.

Your thoracic duct and another duct, called your right lymphatic duct, are the two main pathways that help lymph return to your bloodstream. Your right lymphatic duct drains lymph from your right arm and the right sides of your head, neck and chest. Your thoracic duct drains lymph from all the other parts of your body, including:

• The left sides of your head, neck and chest
• Your belly (abdominal) area
• Both of your legs

What is the function of the thoracic duct?

Your thoracic duct collects lymph from many smaller lymphatic vessels throughout your body. It delivers this lymph to your circulatory system. This helps support healthy fluid levels and allows your body to filter out waste.

Here’s what that process looks like:

• Lymph from small lymphatic capillaries flows into larger lymphatic vessels.
• These larger vessels — sometimes called tributaries — drain into your thoracic duct. Picture side streets joining up with a main road. Your thoracic duct is that main road.
• Your thoracic duct keeps the lymph moving upward until it reaches the lymphovenous junction (LVJ). This is where your thoracic duct connects with one or more veins at the base of your neck, on the left side.
• Like cars merging onto a highway, lymph flows from your thoracic duct into your veins. From there, it moves throughout your body as part of your plasma.

Each day, your thoracic duct delivers about 3 liters of lymph into your circulatory system. This includes chyle, a special kind of lymph that’s rich in fats (lipids). Chyle comes from your digestive system. It’s milky-white in color, unlike lymph from elsewhere in your body, which is typically clear.

Where is the thoracic duct located?

Your thoracic duct is in the middle of your chest. It’s close to your aorta, esophagus and spine. It starts near the top of your lumbar spine (between the T12 and L2 vertebrae in most people). That’s where several lymphatic vessels merge — including those that carry lymph from your legs and intestines. These vessels sometimes form a sac-like structure called the cisterna chyli.

From there, your thoracic duct travels upward. It follows a similar course to your spine as it travels through your chest (thorax). Along the way, other lymphatic vessels drain into it. As it nears your neck, it forms an arch that rises just above your collarbone. It then curves back downward to empty into one or more veins in your upper chest.

Where does the thoracic duct drain?

The exact drainage location varies from person to person. Your thoracic duct might drain into the spot where your left subclavian vein and left internal jugular vein meet. Or it might drain into either of these veins, very close to their junction. It’s also possible for it to drain into your left external jugular vein.

Your thoracic duct may lead directly to a vein. This is the case for most people. But there are variations. Your thoracic duct might split into branches before coming back together to form a single terminal (end-point) duct. Or it could split into two ducts that open separately into your veins.

You might not need to know the exact anatomy of your thoracic duct. But healthcare providers keep it in mind when doing certain procedures and surgeries.

What’s the structure of the thoracic duct?

Your thoracic duct is shaped like a tube. It has many other tubes — smaller lymphatic vessels — connected to it. The walls of your thoracic duct have three layers. These are called the intima, media and adventitia. Smooth muscle tissue in the middle layer (media) squeezes regularly. This keeps lymph moving in the right direction.

As lymph flows through the duct, it encounters valves at various points. These valves open and close to further help lymph along on its journey.

Your thoracic duct is anywhere from 38 to 45 centimeters long. Its opening (diameter) varies along its length from 2 to 5 centimeters.

What conditions can affect my thoracic duct?

Conditions that may keep your thoracic duct from working properly include:

• Chyle leak. This is when fatty lymph (chyle) leaks out of your thoracic duct into nearby tissues. Such a leak can occur as a complication of surgery or from trauma.
• Chylothorax. This is a specific type of leak where chyle enters the space around your lungs. It’s a form of pleural effusion. It can cause trouble breathing, chest tightness and fatigue.
• Congenital blockage. It’s possible to be born with a thoracic duct that’s not fully formed. The duct might end too soon or fail to open into a vein, blocking lymph flow. This typically occurs in babies with severe congenital heart disease.

Treatment depends on the condition but may include:

• Temporary changes to what you eat or drink
• Medications
• A procedure to drain fluid (thoracentesis)
• A surgery to tie off the duct (thoracic duct ligation)
• A procedure to purposefully block the duct (thoracic duct embolization)

Your healthcare provider can tell you more about what to expect in your situation.

If you’re having surgery on your chest or belly, your provider will tell you if thoracic duct injury is a possible complication. They’ll also tell you what signs to look out for as you recover.