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Lymphatics of the mediastinum

Lymph nodes and vessels of the mediastinum and thoracic cavity.

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Hello everyone! This is Joao from Kenhub, and welcome to our tutorial on the lymphatics of the mediastinum. In this video, we're going to delve into the world of the mediastinal lymphatics and get to grips with the anatomy involved here. We're going to focus on two major points of interest which are the major lymphatic vessels associated with the mediastinum as well as the lymph nodes found here. Once we've done that, we're going to look at some related clinical notes to add a practical element to our tutorial today. But before we begin, let us quickly define what the lymphatic system actually is.

One of the things that we were talking about when we we're preparing this tutorial is that the lymphatic system is often somewhat known as the forgotten child of anatomy even though this is a very important system in your body. Essentially, it is a part of the cardiovascular system and that it's a network of lymphatic vessels and nodes as you can see in this image now displayed on your screen. The lymphatic system carries a clear watery fluid known as lymph which is drained from all the various tissues in your body and lymph has a similar makeup to blood plasma in that it contains things such as water, nutrients and hormones. It also contains many lymphocytes which are concentrated in the lymph nodes and help to fight off infections.

The lymphatic system plays an important role in our immune system in addition to removing extracellular toxins and waste products from tissues and organs. Remember after it's filtered, all lymph gets returned to the bloodstream so it can be recirculated and processed around the body.

Now that we know what the lymphatic is, let us quickly define the mediastinum before moving forward, and the mediastinum is the area found around the midline within the thoracic cavity which is the green highlight on the image here. And from this anterior view, we can see that it's located between the left and right pleural sacs which are the coverings of the lungs. When looking at the lateral section of the thoracic cavity, we can see that the mediastinum extends from the first ribs which are located right here right down the diaphragm which is located around here. The mediastinum is defined anteriorly by the sternum which is the central bone of the anterior thoracic cage and posteriorly by the vertebral column.

The mediastinum can be divided into different compartments. Firstly, it is divided horizontally into the superior mediastinum and inferior mediastinum. The inferior mediastinum is then split into three parts – the anterior mediastinum which is a small space anterior to the heart and pericardium, the middle mediastinum which contains the pericardium and therefore the heart, and the posterior mediastinum which is located between the pericardium and vertebral bodies of the thoracic vertebrae.

Now that we have an understanding of what the mediastinum actually is, let's get started with the lymphatics of the mediastinum in detail. And let's begin by looking at the major lymphatic vessels involved in this region which receive lymph from the lymph nodes before emptying back into the bloodstream. We're going to begin with the thoracic duct which you can see here highlighted in green. This is the largest lymphatic vessel in the entire body and sometimes also referred to as the left lymphatic duct, alimentary duct or Van Horne's canal. It extends from the level of the twelfth thoracic vertebra up to the thoracocervical region at the root of the neck where it then empties its content into the bloodstream usually around the junction of the left subclavian and internal jugular veins which I highlighted for you in blue. The duct is normally around forty to forty five centimeters long and five millimeters in diameter.

The thoracic duct plays a very important role in collecting and draining the body's lymph, however, lymph is not all that it carries. Along with lymph, the thoracic duct also contains emulsified fats forming a substance known as chyle. The thoracic duct drains lymph from everywhere in the body except for the right side of the head and neck, the right upper limb, the right breast, and the right lung, therefore, receiving up to about seventy five percent of lymph in the human body.

We're now changing our image to one of the internal thorax. I would like to introduce two other important lymphatic vessels which are the left and right bronchomediastinal lymph trunks seen here in green, and these are located on either side or lateral to the trachea anterior to the vertebral bodies of the thoracic vertebrae, and posterior to the brachiocephalic veins. Both the left and right bronchomediastinal trunks empty their contents into the bloodstream each of them usually doing so around the junction of the ipsilateral subclavian and internal jugular veins which is around here.

You may also come across this lymphatic vessel which we can see now here in green. This one is known as the right lymphatic duct. The right lymphatic duct is a variable structure meaning that it's not always present and is formed when the right bronchomediastinal lymph trunk unites with the right jugular lymph trunk and right subclavian lymph trunk before reaching its destination.

And just like that, we've covered the major lymphatic vessels of the mediastinum. We'll review all of these vessels again at the end of this tutorial but in the meantime, you will be hearing more about these vessels throughout the tutorial as most of the lymph nodes which we are about to meet drain into these vessels which we have just studied.

Now let's get started with our lymph nodes of the mediastinum. We're going to be using this particular image quite a bit while we review the lymph nodes of the mediastinum. Let's quickly familiarize ourselves with it. Beginning anteriorly, we have the heart seen here with the pericardial sac. Superior to this, we have the major vessels which enter and leave the heart, notably the superior vena cava, the ascending aorta as well as the pulmonary veins and artery. Posterior to these vessels is the trachea with its semicircular cartilages and this muscular tube behind the trachea is and that's right, you guessed it, we're looking at the oesophagus.

Just lateral to the oesophagus, we have the thoracic duct which we have just learned about. Finally, on the posterior wall of the thorax, we have the vertebral bodies of the thoracic vertebrae with the ribs and intercostal muscles of the thoracic wall lateral to this as you can see here. We can see the diaphragm right here at the bottom of our image which forms the floor of the thoracic cavity. Scattered throughout the thoracic cavity in this image, you will see several lymph nodes and vessels which are seen here in yellow.

We're going to begin now with the brachiocephalic lymph nodes which we can see now highlighted in green. The brachiocephalic lymph nodes which are found in the anterior part of the mediastinum in front of or anterior to the brachiocephalic veins which are these vessels I've just annotated here. These nodes are also known as the anterior mediastinal or prevascular nodes. The brachiocephalic lymph nodes receive lymph from the thymus, the thyroid glands, the pericardium as well as the heart. The efferent lymphatic vessels from the brachiocephalic nodes drain into the ipsilateral bronchomediastinal trunk which we learn about it earlier in this tutorial.

Now we're going to move to the middle of the mediastinum. The first lymph nodes we are going to meet here are the tracheobronchial lymph nodes. These are a large collection of lymph nodes which are located around the trachea and bronchi of the lungs. The tracheobronchial lymph nodes can be divided into four main groups based on their specific location. These are the paratracheal, superior and inferior tracheobronchial, bronchopulmonary, and intrapulmonary lymph nodes.

Looking specifically at the paratracheal nodes, we can see here that they are found mainly running along either side of the trachea. They receive lymph from the lungs, larynx, laryngopharynx, trachea, thyroid gland, and oesophagus. The paratracheal nodes drain primarily into the ipsilateral bronchomediastinal lymph trunk. Just inferior to the paratracheal nodes are these nodes here which are the superior and inferior tracheobronchial nodes. As their name suggests, the nodes are found around the superior and inferior aspects of the main bronchi reaching as far up as the tracheal bifurcation which explains why they are also sometimes referred to as the bifurcation nodes.

The superior and inferior tracheobronchial nodes receive much of the lymph drained off the lungs via the bronchopulmonary nodes which are found in the hilum of each of the lungs and intrapulmonary nodes found within the lung itself. This lymph when filtered from these nodes then leaves the superior and inferior tracheobronchial nodes to drain into the paratracheal nodes which we have just looked at.

To learn more about these lymph nodes, don't forget to check out one of our other video tutorials where we discuss in more detail about the lymphatics of the lungs.

Continuing on with the lymph nodes, we are now moving into the posterior mediastinum where we have the appropriately named posterior mediastinal lymph nodes. These are located between the region of the hilum of the lung and the superior surface of the diaphragm posterior to the pericardium, anterior to the descending thoracic aorta which I have drawn for you as well as lateral to the oesophagus. You can see the nodes highlighted on this illustration in green.

The posterior mediastinal nodes are sometimes divided into several subgroups depending on their location. For example, the juxtaoesophageal and the juxtaaortic nodes. The prefix juxta- means "near or adjacent to" therefore we can tell that these subgroups are located near to the oesophagus and the aorta respectively. The posterior mediastinal nodes drain lymph away from the oesophagus, posterior pericardium, and posterior surface of the diaphragm which in turn goes on from the posterior mediastinal nodes to drain into the paratracheal nodes or sometimes the thoracic duct.

Staying in the posterior thorax, I would quickly like to mention these nodes now highlighted in green which are the intercostal lymph nodes. These are located in the posterior intercostal spaces close to the heads and necks of the ribs. The intercostal lymph nodes drain deep lymph vessels from the posterolateral part of the thoracic wall, the parietal pleura of the lungs and the breasts as well as the vertebral column and deep muscles of the back. The efferent vessels from the fourth to seventh intercostal spaces unite to form a common trunk. This trunk then descends to the abdominal confluence of lymph trunks or sometimes the start of the thoracic duct.

Meanwhile, intercostal lymph vessels from the left upper intercostal spaces terminate in the thoracic duct. In contrast, the lymph nodes in the right upper spaces variably empty into one of the right lymphatic trunks such as the right bronchomediastinal or subclavian lymph trunks.

We are now going to turn our attention to the floor of the mediastinum which is, of course, defined by the respiratory diaphragm. Here we are going to look at another set of lymph nodes which are called the superior phrenic lymph nodes also known as the superior diaphragmatic lymph nodes.

The superior phrenic nodes comprised three groups of small nodes. These are referred to as the anterior nodes also known as the prepericardial nodes, the lateral nodes, and posterior nodes. They are found across the superior surface of the diaphragm. These lymph nodes drain lymph from the liver, diaphragm, pericardium, diaphragmatic pleura of the lungs, and lowest intercostal spaces.

Meanwhile, they drain into the posterior mediastinal nodes which we have just looked at as well as the parasternal mediastinal nodes which are located in the anterior chest wall on either side of the sternum as you can see here. The efferent vessels of the parasternal lymph nodes unite with those of the tracheobronchial and brachiocephalic nodes to then form the bronchomediastinal trunks.

It's all coming together now, right?

So now we're going to move on to our final group of nodes which I would like to introduce to you today. They are the supraclavicular nodes and they can be seen now highlighted in green on the screen. The supraclavicular nodes are clinically and extremely important group of nodes to be aware of, so make sure to pay close attention to these lymph nodes as I go through them.

As their name suggests, the supraclavicular lymph nodes are a group of lymph nodes located above or superior to the clavicle or collarbone close to the hollow part of the neck near the jugulosubclavian junction which you will remember is the junction of the subclavian and internal jugular veins. The right supraclavicular lymph nodes are closely associated with the vessels of the right lymphatic duct, in particular, the right bronchomediastinal trunk. With this in mind, we know that the right supraclavicular lymph nodes, therefore, drain and filter lymph from the midsection of the chest, the oesophagus and most of the lungs.

Turning now our attention to the left supraclavicular lymph node which is also commonly known as the Virchow's node or sometimes the signal node. The left supraclavicular lymph node is closely associated with the thoracic duct, meaning it drains lymph from the parts of the left thorax as well as all of the abdomen and lower extremities. The left supraclavicular node is perhaps one of the most well-known and best defined lymph nodes in the entire body. So stay with me and we'll shortly find out why that is.

And that completes our lymphatic tour of the mediastinum and surrounding areas. We're going to recap what we have just learned today in just a moment. But first let's have a look at some clinical notes related to what we've learned.

Our clinical note today is going to touch on the topic of lymphadenopathy. Lymphadenopathy is a term used to describe the abnormal or irregular enlargement of lymph nodes. It can be caused by several conditions such as infection, autoimmune disorders and cancer. The link between lymphadenopathy and cancer stems from the fact that the lymphatic system is by far the predominant means for spreading of several types of cancer. As malignant cells metastasize or leave their primary tumor site, they can often accumulate or proliferate within the lymph nodes causing them to then become enlarged.

You may remember that I mentioned earlier that the supraclavicular lymph nodes were of great clinical importance. This is because lymphadenopathy or enlargement of the supraclavicular nodes is considered to be a classic sign of metastatic cancer. Enlargement of the right supraclavicular nodes can indicate malignancies related to the upper right half of the body, in particular, the right lung as well as the inferior lobe of the left lung.

Now, enlargement related to the left supraclavicular node which we also said is known as the Virchow's node can be related with anywhere which eventually drains into the thoracic duct as seen on this image. That being said, an enlarged Virchow's node is especially well known to be associated with cancer of the left lung and stomach or gastric cancer in addition to several other malignant conditions in other abdominal and pelvic organs, for example, duodenal, pancreatic, liver, renal, ovarian, and prostate cancer in man. Enlargement of the left supraclavicular node subsequent to the condition of metastatic cancer is commonly known as the Troisier's sign.

And that's it, we are done and dusted. Let's finish this tutorial off with a quick summary.

So to recap, we began with identifying the major lymphatic vessels of the mediastinum which were the thoracic duct, the right lymphatic duct as well as the right and left bronchomediastinal trunks. We then looked at the major groups of lymph nodes of the mediastinum which included the brachiocephalic lymph nodes, the tracheobronchial lymph nodes, the posterior lymph nodes, the intercostal lymph nodes, the superior phrenic lymph nodes and, finally, the supraclavicular lymph nodes.

And that bring us to the end of this tutorial. I hope you enjoyed watching and I look forward to seeing you on the next one.

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