Video: Nerves of the intercostal space

Do you know that you can feel pain in one part of your body that is in fact caused by an injury or painful stimulus that originates in another part of your body? For example, pneumonia with inflammation of the costal parietal pleura of the lung can induce abdominal pain as well as tenderness and rigidity of the abdominal wall muscles. This phenomenon is called referred pain. Are you curious to understand why this happens? In order to do so, we need to spend some time exploring the nerves of the intercostal space.

In today's tutorial, we will begin with a quick look at the structure, contents, and organization of the intercostal space. We will then move on to take a closer look at the nerves of the intercostal space right from their origin at the spinal cord. We'll give special attention to the intercostal nerves which originate from the thoracic spinal cord and course through the intercostal spaces. We'll describe their formation and associated branches, and finally, the areas they supply. To finish up, we will take a look at a clinical scenario relevant to the nerves of the intercostal space which will help to consolidate and apply our knowledge. So without further ado, let's begin with taking a look at the anatomical structure of the intercostal space.

The 11 paired intercostal spaces are bordered by the rib above and below and contain the intercostal muscles, nerves, arteries, veins, and investing fascia of the thoracic wall. Within each intercostal space, you can find the three groups of intercostal muscles – external, internal, and innermost as well as the intercostal artery, nerve, and vein and their associated branches.

The intercostal artery, nerve, and vein are collectively known as the intercostal neurovascular bundle. Each neurovascular bundle lies in the costal groove along the inferior margin of the superior rib and passes between the inner two layers of muscles. The neurovascular bundle is arranged as vein, artery, and nerve from the most superior to the most inferior. An easy way to remember that is to use a mnemonic VAN. Along the superior border of the rib below within the intercostal space is another neurovascular bundle known as the collateral neurovascular bundle but we'll find out more about it later on.

Now that we have a good understanding on the structure of the intercostal space, let's take a closer look at the nerves within this space, starting right from the beginning with the spinal cord. We can see it highlighted in green, sitting within its meningeal coverings and running through the vertebral canal. All of the nerves of the intercostal space arise from the spinal cord which we'll take a closer look at now.

Extending along the length of the spinal cord are 31 pairs of spinal nerves which are named after the vertebral level they originate from. Located within the thoracic region are the 12 thoracic spinal nerves. The thoracic spinal nerves contribute to the innervation of the intercostal spaces and transmit mixed, motor, and sensory impulses. From the superolateral view of an isolated intercostal space, we can observe that as the spinal nerves extend from the spinal cord they split into posterior and anterior rami. We'll take a closer look at the anterior and posterior rami of the thoracic spinal nerves now, beginning with the posterior ramus.

The posterior ramus emerges from the spinal nerve and courses in a posteroinferior direction. It then divides into two branches – a lateral and a medial branch. The posterior ramus innervates some deep back muscles and also provides sensory cutaneous innervation to the skin of the back. Now let's turn our attention to the anterior ramus of each spinal nerve.

At the thoracic level, the anterior rami of the spinal nerves are also known as the intercostal nerves. Each intercostal nerve travels within the intercostal space between ribs 1 to 11 along with the posterior intercostal artery and vein and receives communicating branches from the white and grey rami communicantes. The anterior ramus of the 12th thoracic spinal nerve runs below the 12th rib within the subcostal space and is therefore known as the subcostal nerve.

Intercostal nerves can be classified as typical or atypical according to their course and branches. Intercostal nerves 3 to 6 are classified as typical intercostal nerves. Typical intercostal nerves enter the posterior intercostal space and initially course within the endothoracic fascia between the parietal pleura and internal intercostal membrane. As the intercostal nerves approach the angle of the ribs, they pass between the internal intercostal and the innermost intercostal muscles. The intercostal nerves, arteries, and veins continue along their course within or just inferior to the costal groove and are therefore protected by the inferior margins of the overlying ribs. Branches of typical intercostal nerves include collateral, lateral cutaneous, anterior cutaneous, and muscular branches. We'll explore each of these branches a little later on.

Intercostal nerves 1, 2, and 7 to 11 are classified as atypical intercostal nerves. Intercostal nerve 1 differs from the typical presentation as it initially divides into a superior and inferior branch on entering the intercostal space. The superior branch joins the brachial plexus and the inferior branch carries on as the first intercostal nerve. The first intercostal nerve along with the second intercostal nerve courses along the internal surface of the first and second ribs instead of along the inferior margin of each rib in costal grooves as we can see here in this anterior view. From this posterior view, we can see that the first intercostal nerve does not usually give off anterior or lateral cutaneous branches, however, the second intercostal nerve may give rise to a lateral cutaneous branch known as the intercostobrachial nerve.

Intercostal nerves 7 to 11 differ according to their course. They begin their journey similar to typical intercostal nerves as we can see from this posterior view. As they extend, they similarly give off anterior and lateral cutaneous branches. However, if we take a look from the anterior view, we can see that after giving rise to their associated lateral cutaneous branches, they cross the costal margin posteriorly and continue anteriorly to supply abdominal skin and muscles. Although they begin their course within the intercostal spaces, as they pass anteriorly, they no longer travel between each rib and are therefore also known as the thoracoabdominal nerves.

Intercostal nerves innervate the muscles within intercostal spaces and a few other muscles of the thoracic wall, the parietal pleura of the lungs, and give off a few branches which provide sensory innervation to the skin of the thorax. Because the intercostal nerves are arranged in such an organized way, the areas of skin they innervate can be demonstrated as a pattern of neatly stacked strips known as dermatomes.

A dermatome is an area of skin that is mainly supplied by a single spinal nerve. The dermatome currently highlighted is the one supplied by the spinal nerve T4. As we have already seen, intercostal nerves 7 to 11 also provide motor innervation to some of the muscles of the abdominal wall and sensory innervation to the skin and peritoneum of the anterolateral abdominal wall. That's why a disease in the thoracic wall may be manifested as pain in the dermatome that extends across the costal margin into the anterolateral abdominal wall. We'll look at a few of the branches of the intercostal nerves next moving from posterior to anterior.

As the intercostal nerves travel anteriorly just medial to the angle of the rib, they give off a collateral branch. 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. The collateral branch of the intercostal nerve travels alongside the collateral branch of the intercostal artery and vein within each intercostal space. The collateral branches of the intercostal nerve, artery, and vein form the collateral neurovascular bundle. This neurovascular bundle runs along the superior border of the rib in the lower part of the intercostal space in reverse order. So instead of vein, artery, and nerve or VAN, the collateral neurovascular bundle is nerve, artery, vein or NAV. Each collateral branch contributes to the innervation of the intercostal muscles and parietal pleura of the lungs.

One main branch that arises from the intercostal nerves is the lateral cutaneous branch. It arises at about the midaxillary line, pierces the internal and external intercostal muscles, and travel superficially to the skin where they provide innervation. The lateral cutaneous branch bifurcates into two terminal branches, one of which travels anteriorly and one that travels posteriorly. These terminal branches supply the skin of the lateral thoracic and abdominal walls.

Anteriorly in the intercostal space near the sternum arises the anterior cutaneous branch of the intercostal nerve. This nerve provides a sensory innervation to the skin of the anterior aspect of the thorax and abdomen. This branch arises just before the intercostal nerve reaches the level of the internal thoracic artery. It pierces the muscles and membranes of the intercostal space, travel superficially to the skin, and divides into medial and lateral branches. Along their course, the intercostal nerves give off numerous slender muscular branches. These small branches provide motor innervation to the intercostal, subcostal, transversus thoracis, and serratus posterior muscles.

Now that we have identified the nerves of the intercostal space, let's have a quick peek at a clinical correlation to this topic.

Intercostal neuralgia is a generalized term used to describe any painful condition related to the intercostal nerves. It can be described as an inflammation to the intercostal nerves. Causes of intercostal neuralgia can vary. The two most common causes are thoracic wall tissue and nerve damage from thoracotomy pain syndrome and herpes zoster infection. Less common causes include trauma, pregnancy, and surgical complications. Symptoms of intercostal neuralgia include sharp, aching, radiating, burning or stabbing pain to the intercostal spaces. There may also be associated paresthesia and numbness typical of neuropathic pain. The pain may be intermittent or continuous. Treatment may vary, according to the cause of the intercostal neuralgia; however, it generally involves pain management, nonsteroidal anti-inflammatory drugs, and topical treatments. In more severe cases, an intercostal nerve blockade may be necessary.

Before we finish this tutorial on the nerves of the intercostal space, let's go over a quick summary.

We began this tutorial with the spinal cord itself. Arising from the spinal cord within the thoracic region, we found the 12 pairs of thoracic spinal nerves. We identified the anterior and posterior rami of the thoracic spinal nerves and explored how they contribute to the innervation of the thoracic wall. We took a closer look at each of the spinal branches beginning with the posterior ramus of the thoracic spinal nerves and two of the branches that arise from it – firstly, the lateral branch of the posterior ramus of the spinal nerve, and secondly, the medial branch of the posterior ramus of the spinal nerve. Finally, we looked at the intercostal nerve or anterior ramus of the thoracic spinal nerve which travels along the intercostal spaces. We identified intercostal nerves 3 to 6 to be typical while intercostal nerves 1, 2, and 7 to 11 are classified as atypical intercostal nerves. We explored the main branches of the intercostal nerves which include the collateral, lateral cutaneous, anterior cutaneous, and muscular branches. We finished by looking at intercostal neuralgia, an inflammation of the intercostal nerves most commonly a result of thoracotomy pain syndrome or herpes zoster infection.

And that's it for today. Hope you enjoyed this video. Happy studying and see you next time.