Video: Blood vessels of the thoracic wall

What do we have here? A battle scene. Huh? This guy is going armorless. He's trusting in his body's natural armor – his thoracic wall. Apparently, the bony framework and muscles of his thoracic wall are strong enough to protect his internal structures. Hmm… But regardless, in order to perform their role, the bones and muscles of the thoracic wall need to be supplied with blood containing nutrients and oxygen. So in today's tutorial, we'll learn all about the blood vessels of the thoracic wall.

First of all, let's take a run through of what we're going to cover in this tutorial. We'll start by looking at the thoracic wall and explore its structure and functions. We'll then move on to the main topic of this tutorial – the blood vessels. Here we will first take a look at some of the major vessels which supply and drain the thorax before diving in to explore the vascular network specific to the thoracic wall. Blood vessels of the thoracic wall can be divided into two separate parts – the arteries and veins of the anterior thoracic wall and the vessels of the posterolateral thoracic wall. Finally, we will discuss some clinical notes to put what we have learned into perspective. So let's begin with exploring the function and anatomical structure of the thoracic wall.

Before we begin to look at any blood vessels, we need to define the area we are working with today. The thorax is the superior part of the trunk, located between the neck and the abdomen. The thoracic wall forms the external boundary of the thorax. It consists of a skeletal framework, neurovasculature, fascia, and muscles, all connected together to form a strong and protective, yet flexible cage.

Today we're only focusing on the thoracic wall vasculature; the arteries and veins which supply the bones, the muscles between them, and the overlying fascia and skin. We will not explore the vessels which supply any organs or tissues within the thoracic cavity. All the blood vessels in the thoracic wall can be traced back or forwards to a few major blood vessels or one of their larger branches. So before we look at a specific region, let's learn about the major vessels of the thorax.

First, let's talk about the aorta, the largest and most important artery in the body, which arises from the left ventricle of the heart. As it passes through the thorax and abdomen, it is defined according to several divisions which we'll take a look at from a lateral view. The ascending aorta is the first segment which arises directly from the left ventricle of the heart and ascends in the thoracic cage as far as the trachea. Continuous with the ascending aorta is an upside down U-bend where the aorta starts its downward trajectory. It is known as the aortic arch and is the most superior point of the aorta.

The next segment we'll look at is the descending aorta. The descending aorta can be further divided into the descending thoracic aorta which extends down the thoracic cavity to the aortic hiatus of the diaphragm at the T12 vertebra and the abdominal aorta.

The ascending aorta, aortic arch, and descending thoracic aorta are sometimes collectively known as the thoracic aorta.

Now let's have a quick chat about the superior vena cava. This vessel is contained in the superior thorax and ends at the level of the third costal cartilage. It carries deoxygenated blood mainly from the upper half of the body to the right atrium. Its main tributaries are the left and right brachiocephalic veins and the azygos venous system. We'll be touching on these later on.

Now that we're familiar with the course of the major blood vessels in the thorax, let's see how their branches and tributaries are distributed in the anterior thoracic wall.

When it comes to the arterial blood supply of the thoracic wall, there is one pair of arteries which arise both directly and indirectly from the aortic arch that we need to know – the subclavian arteries. The left subclavian artery is a direct branch of the arch of the aorta. Medial to the left subclavian artery is the left common carotid artery. The right subclavian artery arises from the brachiocephalic trunk at the level of the right sternoclavicular joint. The subclavian arteries give rise to the internal thoracic arteries and costocervical trunks which extend and branch to supply structures of the thoracic wall. They also give off the thyrocervical trunks, dorsal scapular arteries, and vertebral arteries, but these arteries do not supply the thoracic wall.

Now let's take a look at each of the branches of the subclavian arteries that supply the thoracic wall a bit closer.

The costocervical trunk arises from the second part of the subclavian artery posterior to the anterior scalene muscle. From its origin, it arches in a posterior direction over the cervical pleura extending towards the neck of the first rib where it gives rise to the supreme intercostal and deep cervical arteries. The supreme intercostal artery contributes to the arterial supply of the thoracic wall while the deep cervical artery does not. The supreme intercostal artery travels in a posteroinferior direction along the surface of the neck of the first and second ribs where it gives rise to the first and second posterior intercostal arteries. The supreme intercostal artery is also sometimes known as the superior intercostal artery or highest intercostal artery. We'll talk more about the posterior intercostal arteries a little later on.

Within this lateral view of the thoracic wall, we can see that the internal thoracic arteries arise from the subclavian artery and descend almost vertically posterior to the costal cartilage on the anterior thoracic wall. From this posterolateral perspective, we can see that the internal thoracic artery gives off several branches which supply the thoracic wall. These branches include the sternal and perforating branches as well as the numerous anterior intercostal arteries. At the level of the sixth costal cartilage, the internal thoracic artery terminates by dividing into musculophrenic artery and superior epigastric artery. Let's take a closer look at each of these branches.

First up, we have the anterior intercostal arteries. There are nine pairs of anterior intercostal arteries which occupy the upper nine intercostal spaces. The first six anterior intercostal arteries arise directly from the internal thoracic artery whereas anterior intercostal arteries 7 to 9 originate from one of its terminal branches – the musculophrenic artery. The lowest two intercostal spaces do not receive arterial supply from the anterior intercostal arteries.

If we switch back to the posterolateral view of a section of the thoracic wall, we can take a closer look at how the anterior intercostal arteries enter and travel within the intercostal space. The anterior intercostal arteries extend laterally along the upper portion of each associated intercostal space within the costal groove of the rib above. Promptly after its origin point, each anterior intercostal artery gives off a collateral branch which travels parallel to the upper edge of the rib below. The anterior intercostal arteries also give off several perforating cutaneous branches. Along the lateral aspect of the thoracic wall, the anterior intercostal arteries anastomose with the posterior intercostal arteries and supply the intercostal and pectoral muscles as well as the breast and skin via its branches.

Visible from this posterolateral aspect are a collection of several short arteries located along the posterior aspect of the sternum which are quite fittingly known as the sternal branches of the internal thoracic artery. They supply the periosteum on the posterior aspect of the sternum, sternal bone marrow, and transversus thoracis muscle of the thoracic wall.

Moving on to the next group of branches, we meet the perforating branches of the internal thoracic artery. As the name suggests, they perforate or penetrate onto the anterior surface of the anterior thoracic wall which we can now see from this anterior view. These branches pass onto the anterior surface adjacent to the sternum in the first five or six intercostal spaces. They supply the pectoralis major muscle and give off cutaneous branches which supply overlying skin.

Next, we'll take a look at one of the terminal branches of the internal thoracic artery. The musculophrenic artery descends posterolaterally along the posterior aspect of the seventh to ninth costal cartilages. It pierces the diaphragm at the eighth or ninth costal cartilage and terminates opposite the last intercostal space. It gives off two anterior intercostal arteries which travel within intercostal spaces 7 to 9. The lower portion of the artery also contributes to the supply of the abdominal wall.

The other terminal branch of the internal thoracic artery – the superior epigastric artery – does not supply regions of the thoracic wall but takes part in the blood supply of the anterior abdominal wall.

Now let's take a look at the main veins of the anterior thoracic wall beginning with the anterior intercostal veins.

The anterior intercostal veins travel within intercostal spaces 1 to 9 alongside the anterior intercostal arteries and intercostal nerves as we can see in this posterolateral view of the thoracic wall. They course within the costal groove of the rib above and drain each intercostal space. Within the intercostal neurovascular bundle of the costal groove, the vein is the most superior structure followed by the artery and then the nerve. An easy way to remember the arrangement of the intercostal neurovascular bundle is to simply think of VAN – vein, artery, nerve.

The anterior intercostal veins extend in an anterior direction where they drain into either the internal thoracic vein or the musculophrenic vein. The first six pairs of the anterior intercostal veins drain directly into the internal thoracic vein. The seventh to ninth anterior intercostal veins will first drain into the musculophrenic vein which then drains into the internal thoracic vein.

The musculophrenic veins are formed by the union of the anterior intercostal veins of the lower intercostal spaces, specifically, from intercostal spaces 7 to 9. They ascend along the margin of the ribs in close proximity to the musculophrenic artery and empty into the internal thoracic veins at the level of the sixth costal cartilage. The musculophrenic veins drain the muscles of the lower intercostal spaces as well as the lower portion of the pericardium.

The internal thoracic veins course adjacent to the internal thoracic arteries along the posterior aspect of the sternum and empty into the brachiocephalic veins on either side. Its main tributaries are the anterior intercostal, perforating cutaneous, musculophrenic, and superior epigastric veins. The internal thoracic vein drains regions of the chest wall and breast tissue through its branches as well as parts of the abdominal wall via the superior epigastric veins.

We've covered the major blood vessels of the anterior thoracic wall. Now it's time to see what's going on in the back. Let's take a look at the blood vessels of the posterolateral thoracic wall.

There are 11 pairs of posterior intercostal arteries in total – one pair for each intercostal space. As we mentioned earlier, the most superior two arise from the supreme intercostal artery of the costocervical trunk. The other nine pairs originate directly from the posterior aspect of the descending thoracic aorta. Due to the thoracic aorta being displaced towards the left of the vertebral column, the right posterior intercostal arteries must travel along the longer course to enter the right intercostal space.

Returning to this posterolateral view, we can see the posterior intercostal arteries traveling within the costal groove of the rib above between the intercostal vein and nerve. Similar to its anterior counterpart, the posterior intercostal artery sits sandwiched between the vein and nerve. As the posterior intercostal arteries extend laterally through the intercostal space, they give off several branches – the dorsal, collateral, muscular, and lateral cutaneous branches – which supply structures of the posterolateral thoracic wall.

Posterior intercostal arteries one to nine terminate by anastomosing with the anterior intercostal arteries at the lateral aspect of the thoracic wall. However, it is important to note that there are no anterior intercostal arteries within the 10th and 11th intercostal space. That means that these spaces are supplied solely by the posterior intercostal arteries. We'll take a closer look at each of these branches of the posterior intercostal arteries now.

The dorsal branch arises from the posterior intercostal arteries near the neck of the respective rib. Each dorsal branch gives off a spinal branch which extends to supply the associated vertebra, spinal cord, and meninges before dividing into a medial and lateral dorsal musculocutaneous branch. The medial and lateral dorsal musculocutaneous branches supply vertebrae, the spinal cord, and meninges, and some of the muscles of the back, namely, the spinalis, longissimus thoracis, iliocostalis, the medial aspects of the latissimus dorsi, and trapezius muscles as well as the overlying skin of the back.

The collateral branch of the posterior intercostal artery arises from the posterior intercostal artery near the angle of the rib. This branch extends within the intercostal space along the superior border of the rib below and is accompanied by collateral branches of the intercostal vein and nerve. Unlike the intercostal bundle, the collateral neurovascular bundle is arranged in reverse order with the nerve above the artery and the artery above the vein. Therefore, to remember the order of the collateral neurovascular bundle of the intercostal space, all you have to remember is nerve, artery, and vein. The collateral branch of the posterior intercostal artery anastomoses with the anterior intercostal arteries and thus supplies the intercostal spaces and thoracic wall.

The muscular branches arise along the length of the posterior intercostal artery and supply the intercostal, pectoral, and serratus anterior muscles of the thoracic wall. These branches terminate by anastomosing with the superior and lateral thoracic branches of the axillary artery.

Onto the final branch, we meet the lateral cutaneous branch of the posterior intercostal artery. The lateral cutaneous branch arises from the posterior intercostal artery at the posterolateral aspect of the intercostal space. It travels in an anterior direction along the respective lateral cutaneous vein and nerve. The lateral cutaneous branch pierces the intercostal muscles and divides into posterior and anterior rami which supply the skin of the posterolateral thoracic wall.

Now moving on to look at the veins of the posterolateral thoracic wall, we meet the posterior intercostal veins. The posterior intercostal veins you'll see have quite an interesting arrangement which in reality displays a large degree of interindividual variation. But today, we'll explore the classic description of these vessels working our way from superior to inferior.

There are 11 pairs of posterior intercostal veins which are accompanied by their arterial counterparts. Each vein receives a tributary posteriorly known as the dorsal branch of the posterior intercostal vein which drains blood from the dorsal muscles, skin, and vertebral venous plexus. The first pair of posterior intercostal veins, also known as the supreme intercostal veins, ascend anterior to the neck of the first rib and drain directly to either the vertebral or brachiocephalic veins. The supreme intercostal vein drains the muscles of the associated intercostal space and back, the upper portion of the vertebral column, and the overlying skin of the thoracic wall.

The second, third, and usually fourth posterior intercostal veins extend and unite to form a superior intercostal vein. The left superior intercostal vein empties into the left brachiocephalic vein while the right superior intercostal vein drains into the arch of the azygos vein, as you can see here. The left and right superior intercostal veins drain structures of the respective intercostal spaces and back as well as the skin of the upper posterior thoracic wall. The superior intercostal vein may also communicate with the supreme intercostal vein which we mentioned previously.

Finally, the 5th to 11th pairs of posterior intercostal veins drain into the azygos-hemiazygos venous system. The right posterior intercostal veins 5 to 11 drain into the azygos vein. On the left, it's a bit more complicated; but don't worry, we'll take a look at a schematic illustration of the azygos-hemiazygos venous system to make things a bit clearer.

Here, the left posterior intercostal veins 5 to 8 generally are said to drain into the accessory hemiazygos vein which is often continuous with the left superior intercostal vein. The left posterior intercostal veins 9 to 11 drain into the hemiazygos vein. The hemiazygos and accessory hemiazygos veins then both empty into the azygos vein. However, we need to remember that the azygos-hemiazygos venous system is subject to a lot of variation, so use the information provided here as a guideline rather than a rule.

We've covered the anatomy of the blood vessels of the thoracic wall, but why is it something that you need to know? Let's turn to some clinical notes to find out.

In this section, we will focus on the clinical importance of the arterial anastomosis of the thoracic wall. In order to do that, let's take a look at a condition known as coarctation of the aorta. Coarctation means narrowing, so in this condition, there is a constriction of the aorta distal to the left subclavian artery. The pressure before the coarctation increases since blood has a harder time squeezing through the narrowed part of the artery. This results in an increased blood flow in the branches of the aortic arch, which are located before the narrowing. For the same reason, the blood flow and pressure downstream from the coarctation decreases, which can markedly reduce blood flow to the lower body.

The increased blood pressure above the narrowing affects the subclavian, internal thoracic, and ultimately, the anterior intercostal arteries. It also affects the first two posterior intercostal arteries as they arise from the costocervical trunk of the subclavian artery. The decreased blood pressure and flow below the narrowing directly affects the 3rd to 11th posterior intercostal arteries which arise from the descending thoracic aorta.

As we mentioned earlier, the anterior and posterior intercostal arteries anastomose with one another in each intercostal space. This anastomosis forms collateral circulatory routes in the event of impeded aortic blood flow. When there is a constriction of the aorta, the blood starts flowing from the high pressure anterior intercostal arteries to the low pressure posterior intercostal arteries creating a reversed or retrograde flow from the posterior intercostal arteries into the aorta. These posterior intercostal arteries dilate to accommodate the high pressure and when the heart beats, they pulsate against the ribs, slowly deforming the surface of the bone. This can be seen on x-ray as rib notching, typically only affecting ribs 3 to 9. Because there is a high pressure in both the anterior and posterior intercostal arteries of the first and second intercostal spaces, there is no reversal of blood flow and therefore no rib notching identified ribs 1 and 2. Treatment options for this condition include balloon dilation and surgery.

And that's this tutorial done and dusted. Let's wrap up everything now with a quick summary of the vessels we looked at today.

In this tutorial, we looked at the veins and arteries supplying the thoracic wall and some of their branches. We first looked at the largest artery in the body – the aorta – and its main divisions in the thorax – the ascending aorta, the aortic arch, and the descending thoracic aorta. We then took a peek at the major vein of the thorax – the superior vena cava. Next, we explored the vasculature of the anterior thoracic wall beginning with the subclavian artery and its branches – the costocervical trunk and internal thoracic artery. These branches are important arterial-supplying structures of the anterior thoracic wall. We explored the supreme intercostal artery, a branch of the costocervical trunk, before turning our attention to the internal thoracic artery and its branches that supply the thoracic wall. These branches include the anterior intercostal arteries, the sternal branches, the perforating branches, and one of its terminal branches, the musculophrenic artery.

Moving on, we then took a quick look at the veins of the anterior thoracic wall. We explored the anterior intercostal veins which empty into the musculophrenic and internal thoracic veins of the thoracic wall.

Next, we meet the blood vessels of the posterolateral thoracic wall starting with the arteries. Here we looked at the posterior intercostal arteries. Branches of the posterior intercostal arteries include the dorsal, collateral, muscular, and lateral cutaneous branches. We then looked at the posterior intercostal veins. The first or supreme intercostal veins drain directly into the brachiocephalic veins. The left superior intercostal vein similarly drains into the brachiocephalic vein while the right superior intercostal vein drains into the azygos vein. The right posterior intercostal veins 5 to 11 drain to the azygos vein while the left posterior intercostal veins 5 to 8 drain to the accessory hemiazygos vein and the left posterior intercostal veins 9 to 11 drain to the hemiazygos vein.

For our clinical notes, we applied our knowledge of the anastomoses formed by the arteries of the thoracic wall to understand the mechanism behind rib notching, seen in a condition called coarctation of the aorta.

And that's all for today. I hope you enjoyed learning about the blood vessels of the thoracic wall. Happy studying and see you next time.