 Good day everybody. Dr. Sanjeev Sanyal, Professor, Department Chair. So this is going to be a demonstration of the posterior aspect of the thoracic wall. I'm standing on the right side of the supine cadaver, camera person is also on the right side. So we have removed the anti-hat chest wall, which is shown here. We have removed the heart. We have removed the lungs. So this is the posterior media stenum. This is the superior media stenum. Let's focus on these neurovascular structures that we can see on the right side and the neurovascular structures that we can see on the left side. The collection of structures which we have picked up here. This is the intercostal neurovascular structures and they follow a regular pattern. The topmost is the vein. Just under that is the artery and then we have the nerve. The same thing is seen here, here and in all the spaces. These neurovascular structures they are running in a shallow groove on the under surface of the rib above that is called the costal groove and therefore they are partially protected. So let's take them one by one. Let's start with the nerve. There are 12-meter costal nerves. The lowest one is called the sub-costal nerve, but some of them are atypical nerves. The first one is an atypical nerve because it does not have a lateral cutaneous branch. It does not have an anterior cutaneous branch. The second one is also an atypical one because it has got a very large lateral cutaneous branch and I will show it to you here. We can see this branch coming out. This is the lateral cutaneous branch coming from the second intercostal space. This is called the intercostal brachial nerve. This supplies the chest wall as well as the medial side of the arm and this is the one which is responsible for referred pain in angina pectoris. The other atypical nerves are the seventh through the limit because they go to the abdomen. They are called thoracoabdominal nerves. And the twelfth one as I said is sub-costal nerve. What are the branches of a typical intercostal nerve? The first two branches are to the thoracic sympathetic trunk and this is the thoracic sympathetic trunk here. And this deletion that we see here, this is a ganglion. So it gives two connections to each ganglion. They are called ramei communicantes, a gray and a white rameus communicants. The next set of branches are a branch which comes below and we can see that here. This is called a collateral branch. The collateral branch runs in relation to the upper border of the rib below and that is present in all the spaces. Then it of course gives multiple muscular branches to all the muscles but it gives two notable branches. One is on the mid axillary line it gives a cutaneous branch and just parasternal line next to the sternum it gives a branch which pierces through and comes out. And that is known as the anterior cutaneous branch and we can see some anterior cutaneous branches if you look carefully here. They are present on either side of the sternum. So these are the branches of the intercostal nerves. This is an axial MRI of a thoracic segment to show the distribution of intercostal nerves. When we have herpes zoster, herpes zoster is a reactivation of childhood chicken pox. The reactivation phase of the varicella zoster virus it travels along these branches and it produces shingles along the intercostal space. And that is what is referred to as varicella zoster or herpes. This is a clinical photograph of varicella zoster or shingles, blisters along the intercostal space. When we are doing any thoracic procedure we have to make sure we do not damage the neurovascular structures which are in relation to the lower border of the rib above. At the same time we also have to safeguard the collateral branches and we also have to anesthetize. Usually we have to anesthetize two adjacent segments in order to get complete anesthesia because there can be some overlap of nerve fibers. So this is about the intercostal nerve. Now let's come to the vein. This is the vein as I told you. There are 12 intercostal veins first year. On the right side the first first intercostal vein as you can see it is not draining into the regular place it is going up. The first one is called the supreme intercostal vein. It drains into the right brachioscephalic vein which is this one here. The second third and fourth spaces they are referred to as the superior intercostal vein. They drain into the azygous vein and the rest also drain into the azygous vein individually. So this is the drainage on the right side. Now we shall take a look at the drainage on the left side. Now we have shifted on the left side of the cadaver and the camera person is also on the left side. Now we can see the same structures on the left side and here we can see more clearly we can see the vein. We can see the nerve and in between we can see the artery which I shall talk about just now. On the left side we can see this vein here. This is the hemias azygous vein. The hemias azygous vein receives the lower 4 pristine intercostal veins. Then we can see yet another vein here. This is the accessory hemias azygous. The accessory hemias azygous is formed by the middle 4 pristine intercostal veins uniting. The hemias azygous opens just below the T8 and the accessory hemias azygous opens just above T8 and both of them open into the azygous vein which I have lifted up here. And we can see it's opening here into the azygous vein. What about the upper 4? The upper 4 constitute what is known as the supreme intercostal on the left side. They all unite and they open independently into the left brachial cephalic vein. This is the drainage of the pristine intercostal veins. Right side mostly they drain into the azygous. Left side they drain into the hemias azygous and the accessory hemias azygous. Now let's come to the artery. We will remain on the left side. Artery is located between the vein and the nerve and we can see that clearly here. The artery can be identified on it will be slightly torches. It will be thicker and it is located between the this is one pristine intercostal artery. This is another pristine intercostal artery. This is yet another pristine intercostal artery that we can see here. These intercostal arteries are in two different sets. One set comes out from the thoracic aorta. And as they come out they give a collateral branch which I mentioned earlier which runs in relation to the rib below. So now two sets of arteries are going like this. And I'm going to bring the anterior chest wall here. On the inner surface of the anterior chest wall we have this artery running here. This is the internal thoracic artery. And we can see it is continuing as the musculophrenic artery here. The internal thoracic artery up to the sixth space gives two anterior intercostal arteries. Musculophrenic gives two anterior intercostal arteries from the seventh to the ninth space. The tenth, eleventh and twelfth spaces do not have any anterior intercostal arteries. So the two anterior intercostal arteries from the front and the posterior intercostal artery and the collateral branch from the back. They are all anastomers. Most of the blood flows from the posterior to the anterior. Here we have a very unique situation and that happens in a condition called coactation of aorta. Coactation is the congenital narrowing of the aorta which happens usually after the ductus arteriosus. So it happens somewhere here that is called the post ductal coactation. This portion of the aorta is narrow and once it is narrow there is no blood flow to the rest of the aorta. So in order to compensate for this lack of blood flow, what happens is the internal thoracic arteries, they become very prominent. They get a lot of blood supply and the blood flow goes through the anterior intercostal arteries. They go in the reverse direction. They go through the posterior intercostal arteries and they flow back to the aorta and that's how it supplies the body. That produces extreme dilatation of the posterior intercostal arteries and they become even more tortuous and that leads to notching of the inferior border of the ribs which is a very important sign of coactation of aorta. This just x-ray shows dilated posterior intercostal arteries with notching of the ribs in coactation of aorta. At the same time, these posterior intercostal arteries which are very dilated, they anastomers with the torsus capillary artery between the scapula and when you put your hand there you can feel the pulsation and that is referred to as dancing scapula. So that's another finding that we can see in coactation of aorta. These are all because of extreme dilatation of the posterior intercostal arteries. This collateral branch applies not only to the arteries, they also apply to the nerves and to the veins which we have already mentioned. Before I conclude about the neurovascular structures, I just need to tell you a give you overview of what was located on the posterior aspect of the inner chest wall. This was covered by two layers, both of which we have removed. One was the shiny layer which is the innermost that is the parietal pleural. We have removed it on both the sides and once we removed that we had another areola tissue layer with a little bit of fat and that is known as the endothoracic fascia which is outside the parietal layer. And once we removed that then only we could dissect out the neurovascular structures and on removing it we now we can see some muscles also. We can see these muscle fibers here. These are the innermost intercostal and the subcostal muscles and we can see the same thing here also. We can see these muscle fibers here. These are the innermost intercostal and the subcostal. This innermost intercostal and the subcostal muscle they constitute the third layer of the chest wall and we notice that these neurovascular structures are disappearing inside that. So therefore the space between the third layer that is the innermost intercostal or the subcostal and the internal intercostal that is considered as the neurovascular plane which is visible only when we remove the endothoracic fascia. So that is about what we can see in the posterior thoracic wall with its neurovascular structures and their clinical correlations.