Video: Blood vessels of the intercostal space

Ever played Operation, Pick-up sticks or Buzz wire before? If you have, you'll know how important a steady hand is. A steady hand also comes in handy when medical doctors need to access the thorax by entering between the ribs. It can be tricky to enter the thorax without hitting the neurovascular bundle of the intercostal space. That's why it's so important to learn about the structures of the intercostal space, specifically, its blood vessels.

In this video, we'll be focusing on identifying these structures from a supralateral view. We'll begin with a quick overview of the bones of the thorax so we're aware of what structures are around these arteries and veins. Then we'll jump into the good stuff and identify the arteries of the intercostal space. We'll start with the thoracic aorta and the branches that arise from this massive artery on the posterior aspect of the thorax. We'll then head anteriorly and look at the internal thoracic arteries and the branches that arise from those. Next, we'll explore the veins of the intercostal space which are known as the anterior and posterior intercostal veins as well as their associated branches. We'll then finish up with some clinical notes surrounding the vasculature of the intercostal space to help consolidate our knowledge. So let's get to it, starting with a quick review of the bones of the thorax.

A thoracic wall is composed of different bones that enclose and protect the thoracic cavity. Anteriorly, we find the sternum – a flat and elongated bone. Posteriorly, the thoracic wall is made up of 12 thoracic vertebrae. Laterally, the thoracic wall is formed by ribs – 12 long and curved bones located on each side of the body. In this tutorial, we'll focus on the spaces between the ribs. These spaces are known as the intercostal spaces and there are 11 of them on either side. These spaces are filled with intercostal muscles. The neurovascular bundle of the intercostal space consisting of the intercostal nerve and vessels lies in the costal groove along the inferior margin of the superior rib and passes between the inner two layers of muscles. In each intercostal space, the vein is the most superior structure, the artery is inferior to the vein and the nerve is inferior to the artery. In this tutorial, we'll be focusing on the blood vessels of the intercostal space.

All right, let's get to the good stuff – onto the arteries of the intercostal space and how to identify them from this supralateral view.

The arteries that supply the thoracic wall consist mainly of the posterior and anterior intercostal arteries. These arteries pass around the thoracic wall in the intercostal spaces being a part of the aforementioned neurovascular bundles. The posterior intercostal arteries originate from the descending thoracic aorta while the anterior intercostal arteries originate from the internal thoracic arteries which in turn rise from the subclavian arteries in the root of the neck. Let's take a look at each of these arteries.

The largest artery is what we'll begin with. This is the descending thoracic aorta. The descending thoracic aorta runs inferiorly along the thoracic vertebrae, offset slightly to the left. This is due to the location of the trachea running along the midline of the posterior thoracic wall. Arising directly from the thoracic aorta are paired posterior intercostal arteries. These arteries travel within the intercostal space anteriorly towards the sternum along the costal groove on the inferior margin of the superior rib. They are some of the arteries that supply the muscles that occupy these intercostal spaces.

There are 11 pairs of posterior intercostal arteries in total – one pair for each intercostal space. Nine of them originate in this way directly from the descending thoracic aorta whereas the most superior two arise from a common supreme intercostal artery.

Along its course, the posterior intercostal artery gives off three branches – the dorsal branch, the collateral branch, and the lateral cutaneous branch. The first branch given off by the posterior intercostal arteries is called the dorsal branch of the posterior intercostal artery. As its name suggests, it travels dorsally or posteriorly from the posterior intercostal artery. It then gives off three branches – the spinal branch travels medially and supplies the vertebrae, spinal cord, and meninges; the lateral cutaneous branch courses alongside the lateral branch of the posterior ramus of the spinal nerve and supplies some of the muscles of the back and the overlying skin; and finally, the medial cutaneous branch which courses alongside the medial branch of the posterior ramus of the spinal nerve and supplies some of the muscles of the back and the overlying skin.

If we cast our eyes back to the posterior intercostal artery, we can then follow it along the intercostal space and find its second branch arising near the angle of the rib – the collateral branch of the posterior intercostal artery. This collateral branch crosses the intercostal space and travels along the superior border of the rib below at the inferior border of its intercostal space. It is accompanied by the collateral branches of the posterior intercostal vein and nerve. The posterior and collateral intercostal arteries anastomose with the anterior intercostal arteries of the same side at the anterior axillary line. This branch contributes to the arterial supply of the anterior, posterior, and lateral aspects of the thoracic wall.

The final main branch of the posterior intercostal artery is the lateral cutaneous branch of the posterior intercostal artery which splits into two branches – one which travels anteriorly and one which travels posteriorly. Just like the other cutaneous branches we've identified, these arteries supply blood to the skin so are more superficial than the intercostal arteries. Following this posterior part, we can see that it meets up with the lateral cutaneous branch of the dorsal branch of the posterior intercostal artery. So the skin over the lateral aspect of the back receives blood via two paths.

As we know, the posterior intercostal arteries can be found between each pair of ribs within the intercostal space. However, just below the 12th rib is another artery known as the subcostal artery which we can see here from this posterior view. The subcostal artery is analogous with the posterior intercostal arteries but is located within the subcostal space rather than an intercostal space. The subcostal artery similarly has a dorsal branch and subsequent spinal branches and functions to provide arterial supply to the thoracic wall.

All of the arteries we've looked at so far originate posteriorly from the thoracic aorta. There are a few more arteries to identify which arise from the anterior part of the thorax. The main arteries which supply the anterior thorax are these two arteries highlighted on either side of the sternum. These are the internal thoracic arteries. The internal thoracic arteries give off branches medially towards the sternum, anteriorly towards the pectoral region, and laterally towards the intercostal spaces.

The medial branches are called the sternal branches of the internal thoracic artery. We can see them running towards the sternum deep to it. They supply blood to the sternum itself. The anterior branches arising from the internal thoracic artery are the perforating branches. These branches traverse the upper five or six intercostal spaces accompanied by the anterior cutaneous branches of the intercostal nerves. These small arteries pierce and supply the pectoralis major muscle and then become cutaneous vessels that supply the overlying skin. The lateral branches arising from the internal thoracic arteries are the anterior intercostal arteries. Similar to the posterior intercostal arteries, they travel in the intercostal spaces along the inferior border of the superior rib supplying the structures that fill those spaces. It is important to note that there are no anterior intercostal arteries within the 10th and 11th intercostal space. This should come as no surprise as ribs 11 and 12 are so short and located posteriorly in the thoracic cage. The posterior intercostal arteries provide the sole arterial supply to these intercostal spaces.

Similar to their posterior counterparts, the anterior intercostal arteries give off a collateral branch which traverses the intercostal space coursing along the superior aspect of the rib below. As we have already identified, the anterior intercostal arteries and their associated collateral branches anastomose with the posterior intercostal arteries and their collateral branches at the level of the anterior axillary line. As a result, the collateral branches contribute to the arterial supply of the thoracic wall.

Okay, now it's time to look at the veins.

The venous drainage of the intercostal spaces generally parallels the arrangement of the arterial supply. The intercostal veins follow the intercostal arteries and nerves throughout their course in the intercostal space and are the most superior structure in the neurovascular bundle. They can similarly be divided into anterior and posterior groups. There are nine pairs of anterior intercostal veins and 11 pairs of posterior intercostal veins. For the most part, the tributaries of these veins follow and have the same name as their accompanying arterial branches. The posterior intercostal veins ultimately drain into the azygos system of veins while the anterior intercostal veins drain into the internal thoracic veins which connect with the brachiocephalic veins in the neck.

Let's take a look at this anterior view of the posterior thoracic wall and discuss the course of the posterior intercostal veins.

The posterior intercostal veins collectively drain the posterior thoracic cavity. It's worth mentioning that we'll describe the most common pattern of venous drainage, however, there is considerable variability amongst individuals. The first posterior intercostal veins or supreme intercostal veins usually drain directly into these two big veins of the thoracic cavity which are named the brachiocephalic veins. The other posterior intercostal veins drain into the azygos system of veins and that's what we'll describe right now.

The right second, third, and often, the fourth posterior intercostal veins come together forming the right superior intercostal vein which in turn drains into the azygos vein – another important vein of the thoracic cavity. Similarly, the left second, third, and occasionally, the fourth posterior intercostal veins unite forming the left superior intercostal vein which in turn drains into the left brachiocephalic vein. The rest of the posterior intercostal veins on the right drain into the azygos vein. On the left, there is no azygos vein. Instead, there is one accessory hemiazygos vein superiorly and a hemiazygos vein inferiorly, so on the left, the 5th to 8th posterior intercostal veins usually drain into the accessory hemiazygos vein while the 9th to 11th drain into the hemiazygos vein.

Similar to its arterial counterpart, the subcostal vein can be found just below the 12th rib within the subcostal space. The subcostal vein unites with the ascending lumbar vein to form the azygos vein on the right and the hemiazygos vein on the left. The subcostal vein drains the upper posterior abdominal wall just inferior to the 12th ribs. Each intercostal space also contains one or two anterior intercostal veins which anastomose with the posterior intercostal veins as they extend posteriorly. The anterior intercostal veins follow the same course as the arteries and drain into the internal thoracic vein superiorly and musculophrenic veins inferiorly. The anterior intercostal veins collectively drain the anterior thoracic cavity.

The musculophrenic veins originate from the union of the lower anterior intercostal veins and ascend obliquely along the margin of the ribs. At the level of the sixth intercostal cartilage, they drain into the internal thoracic veins. The internal thoracic veins are formed as a continuation of the musculophrenic veins and the superior epigastric veins. They accompany the internal thoracic arteries and course superiorly. These veins eventually drain into the ipsilateral brachiocephalic vein.

Let's take a look at some clinical applications surrounding the intercostal space to help consolidate our knowledge.

The thoracic cavity is home to the lungs and trachea, heart and great vessels, thymus, and the majority of the esophagus. The intercostal spaces provide an ideal access point into the chest wall to perform a variety of medical procedures that may involve these structures. Two relatively common examples of these procedures include thoracentesis and video-assisted thoracic surgery. These procedures require knowledge of the neurovascular structures of the intercostal spaces in order to be successful.

A thoracentesis is performed when a patient has a pleural effusion – a condition where there is an excess of fluid in the pleural cavity. This procedure is done to obtain this fluid for analysis in order to determine the cause of the pleural effusion. A chest radiograph will determine the location and size of the effusion and clinical examination will determine the best site for aspiration – the posterior midscapular line is a usual place. More complex or smaller fusions may need to be aspirated under ultrasound guidance.

As we know, the intercostal arteries and veins run along the superior part of each intercostal space in the inferior border of the superior rib. To avoid hitting this neurovascular bundle, the aspiration needle is inserted into the lower portion of the intercostal space along the superior border of the inferior rib until it enters the pleural space.

Minimally invasive thoracic surgery known as video-assisted thoracic surgery requires making a small incision to the center of the intercostal space taking care to avoid neurovascular structures. A camera or thoracoscope is then inserted and transmits images from the inside of the thoracic cavity in order to guide the surgeon who manipulates other instruments inserted through additional small incisions. A number of procedures used to diagnose and treat intrathoracic disorders can be performed with this technique avoiding open chest surgery.

Before we finish up, let's have a quick review of what we looked at today.

We started by looking at the bones of the thorax which protect the arteries and veins of the intercostal space. First, we looked at the sternum anteriorly. Next, we looked at the thoracic vertebrae posteriorly. Finally, we identified the ribs and the intercostal spaces between them. The intercostal neurovascular bundle lies in the costal groove along the inferior margin of the superior rib. Next, we explored the arteries of the intercostal space. We began with the thoracic aorta and looked at the main paired arteries that arise from it – the posterior intercostal arteries.

From the posterior intercostal arteries arise several branches. First, the dorsal branch of the posterior intercostal artery. This branch gives off three branches itself – a spinal artery, the lateral cutaneous branch, and the medial cutaneous branch. Then we met the next branch of the posterior intercostal artery – the collateral branch of the posterior intercostal artery. This branch travels along the intercostal space and sits along the superior border of the lower rib. Finally, we came to the lateral cutaneous branch of the posterior intercostal artery which splits into two branches – one which travels anteriorly and one which travels posteriorly.

Just below the 12th rib within the subcostal space, we identified the subcostal artery which is analogous to the posterior intercostal arteries. From the anterior side, we then identified the internal thoracic arteries. These arteries give off the sternal branches medially, the perforating branches anteriorly, and the anterior intercostal arteries laterally.

We then moved on to have a look at the veins of the intercostal space beginning with the posterior intercostal veins. The posterior intercostal veins are located in each intercostal space. They contribute to the venous drainage of the thoracic wall and ultimately drained to the azygos, accessory hemiazygos, and hemiazygos veins. Similar to its arterial counterpart, the subcostal vein is located just below the 12th rib within the subcostal space. It unites with the ascending lumbar vein to form the azygos vein on the right and the hemiazygos vein on the left. Next, we identified the anterior intercostal veins which anastomose with the posterior intercostal veins at the level of the anterior axillary line. The anterior intercostal veins follow the same course as the arteries and drain into the internal thoracic superiorly and the musculophrenic veins inferiorly.

To finish, we explored the importance of having a good understanding of the neurovascular structures of the intercostal space when performing a thoracentesis or video-assisted thoracic surgery.

That brings us to the end of the tutorial. We hope you enjoyed it. Thanks for joining us and happy studying.