 Okay, ready? 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, seen from inside. I'm standing on the right side of the supine cadaver, camera person is also on the right side. So we have removed the anterior chest wall, which is shown here. We have removed the heart, we have removed the lungs. So this is the posterior mediastinum, this is the superior mediastinum. 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. 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 costive groove. And therefore they are partially protected. So let's take them one by one. Let's start with the nerve. There are 12-bit of costal nerves, the lowest one is called the subcostal 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 to the eleventh because they go to the abdomen. They are called thoracoabdominal nerves. And the twelfth one, as I said, is subcostal 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 dilatation that we see here, this is a ganglion. So it gives two connections to each ganglion. They are called ramai communicantes, a gray and a white ramus 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 the intercostal nerves. When we have herpes zoster, herpes zoster is a reactivation of childhood chickenpox. 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 so that 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 brachiocephalic vein, which is this one here. The second third and fourth spaces, they are referred to as superior intercostal vein. They drain into the azagus vein. And the rest also drain into the azagus 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 carabin. And the camera person is also on the left side. So 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 hemiasagus vein. The hemiasagus vein receives the lower four posterior intercostal veins. Then we can see yet another vein here. This is the accessory hemiasagus. Accessory hemiasagus is formed by the middle four posterior intercostal veins uniting. The hemiasagus opens just below the T8. And the accessory hemiasagus opens just above T8. And both of them open into the azagus vein, which I have lifted up here. And we can see it's opening here into the azagus vein. What about the upper four? The upper four constitute what is known as the supreme intercostal on the left side. They all unite and they open independently into the left brachiosephalic vein. This is the drainage of the posterior intercostal veins. Right side mostly they drain into the azagus. Left side they drain into the hemiasagus and the accessory hemiasagus. Now let's come to the arterial. We will remain on the left side. Arteries are 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 posterior intercostal artery. This is another posterior intercostal artery. This is yet another posterior intercostal artery that we can see here. These posterior 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 just wall here. On the inner surface of the anterior just 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 phase gives two anterior intercostal arteries. Musculophrenic gives two anterior intercostal arteries from the seventh to the ninth phase. The tenth, eleventh and twelfth phases 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 a 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 costal arteries with notching of the ribs in coactation of aorta. At the same time these posterior intercostal arteries which are very dilated they are anastomous 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 an 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 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 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 noticed that these neurovascular structures are disappearing inside that. 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. Thank you very much for watching Dr. Sanjeev Sanyal signing out. If you have any questions or comments please put them in the comment section below. David who is a camera person have a nice day.