 Good day everybody. This is Dr. Sanjay Sanyal, professor of department chair. So this is going to be a demonstration of thyroid gland So just to bring you up to speed. This is a specimen that we have completely excised from a cadaver So this up here. This is the hyoid bone This is the body of the hyoid which has been cut Below that we can see this structure here. This is the thyroid cartilage and we can see this is the Superior thyroid notch. This is the laryngeal prominence. This is the labidum of thyroid and Down below we have the cricoid cartilage the ring of the cricoid cartilage and further below we have the tracheal rings Each of these are attached by means of various ligaments. We have the Thyroid ligament the median and the lateral thyroid ligament Then we have the Crico thyroid ligament between the thyroid and the cricoid and then we have the crico tracheal ligaments which hold all these cartilages together The point to be noted is that the only skeleton which is body is the hyoid bone The rest are all cartilages. These are the Reminders of the infrared strap muscles. This one is the superior belly of the omohide that we have cut This is the sternohyoid on the right side. There's the sternohyid on the left side All the other muscles strap muscles we have completely removed Now let's take a look at the structure which I've been focusing on This is the thyroid gland and we can see this is the right lobe of the thyroid We are completely separated out from here This is the isthmus of the thyroid gland This is the left lobe of the thyroid gland And I will separate it out here We notice in this particular dissection specimen. There is an extra lobe here This is called the pyramidal lobe which is a remnant from the thyroid gloss of duct and as is usually seen in such cases When there is a prominent pyramidal lobe of the thyroid gland the isthmus of the thyroid gland may either be deficient or Completely absent and we can see that exactly here This is the isthmus of the thyroid gland and we can see that it is deficient here So this is that these are the lobes of the thyroid gland The thyroid gland extends from C5 to T1 C5 is just above the correct cartilage and T1 is at the thoracic inlet upper pole and lower pole Now let's take a look at some neurovascular structures that we can see in this. I will start from the top We can see these three neurovascular structures here, which I've lifted up one here The next one here and this one here This is the internal laryngeal nerve Interloar laryngeal nerve is a branch of the superior laryngeal nerve, which is the branch of veins This internal laryngeal nerve it pierces through the lateral thyroid membrane, and it is accompanied by the superior laryngeal artery and the superior laryngeal vein The internal laryngeal nerve is the important one internal laryngeal nerve is the largest subdivision of the superior laryngeal nerve And it supplies the mucus membrane of the larynx above the vocal cord Anesthetists infiltrate local anesthesia here in the thyroid membrane to anesthetize the upper half of the larynx for any endolaryngeal procedure. The superior laryngeal artery is a branch of the superior thyroid artery. The laryngeal vein is a tributary of the superior thyroid vein which drains into the internal jugular vein. The next structure I will draw your attention to is this one here. We can see one artery entering into the upper pole of thyroid gland and a nerve going into this muscle here. This is the cricothyroid muscle. The cricothyroid muscle is the only muscle which is outside the larynx and this is supplied by this branch here. This is the external laryngeal nerve. It is a smaller subdivision of the superior laryngeal nerve, the largest subdivision being the internal laryngeal nerve. So this is the external laryngeal nerve which supplies the cricothyroid and it also gives branches to the inferior pharyngeal constrictor. This is accompanied by the superior thyroid artery. The superior thyroid artery is a branch of the external carotid artery. The same superior thyroid artery gave rise to the superior laryngeal artery here. When we are doing a thyroid surgery, thyroidectomy for example, when we are ligating the superior thyroid artery, we have to ligate it as close to the gland as possible and the reason is very obvious. We can see that the external laryngeal nerve is very close to the superior thyroid artery so therefore, ligating it close to the thyroid gland will safeguard the external laryngeal nerve. If the external laryngeal nerve is injured, the cricothyroid muscle will be paralyzed and the person will develop weakness of voice because the function of the cricothyroid muscle is to tense the vocal cord. It's a tensor of the vocal cord. So this is an important neurovascular relationship that I wanted to show you. Now let's come further lower down. We are still on the right side. We can see this neurovascular structure and this neurovascular structure. This is the recurrent laryngeal nerve. This comes from the vagus. It's a vagus accessory complex and it goes up in the tracheoesophageal group and it enters into the larynx behind the lateral cricothyroid joint and then it becomes known as the inferior laryngeal nerve. This is a mixed nerve. It supplies sensation to the lower half of the larynx and it supplies motor to all the remaining muscles of the larynx except the cricothyroid. And if this is injured, which also can be injured during thyroidectomy because it is closely accompanied by the inferior larynx thyroid artery, then the person will have a hoarseness of voice. On this side, on the left side also, we can see this nerve here and this artery here. This is the recurrent laryngeal nerve and this is the inferior thyroid artery. And it is ligating of the inferior thyroid artery that can injure the recurrent laryngeal nerve. Therefore, the rule of thumb is though there is some controversy about this, some textbooks say that when you are ligating the inferior thyroid artery, you should be ligated as far from the thyroid gland as possible so as to save further recurrent laryngeal nerve. Now that we have seen the thyroid gland from outside, now I shall show you another specimen inside. So this is a supine cadaver, we are standing on the right side. So let me reflect this muscle here. This is the sternum hyoid muscle. The next muscle is the sternum thyroid muscle and this is the superior belly of omohiad. Having reflected that, now we can see another specimen of the thyroid gland in another cadaver in situ. So let's take a look at some of the structures which we could not see in the previous dissection specimen. First of all, we can see this fascia here. This is the visceral component of the pre trical fascia. It's a part of the deep cervical fascia. So this is what we have lifted up here. If there's an infection in relation to the visceral component of the pre trical fascia, the infection can easily travel into the superior and into the atria medestinum, right down to the fibrous pericardium. So that's the first point which I want to draw your attention to. The structure which I have lifted up here, this is the thyroid gland, the right lobe of the thyroid gland. This is the isthmus and further that side is the left lobe which we have not descended out. When I lift it up, we can see this muscle here. This is the same muscle which I had shown you in the previous specimen. This is the cricothyroid muscle. Let me draw your attention to the neurovascular structure that we can see in this particular specimen. First of all, we can see this atria here. This is the superior thyroid atria and we can see the superior thyroid atria coming out from the external carotid artery and we can clearly see it going down. This superior thyroid atria, it enters into the upper pole of the gland and it supplies the superior lateral and anterior aspect of the gland and we can see all that clearly here. What about the supply of the cricothyroid muscle? The cricothyroid is supplied by the external laryngeal nerve. This is the external laryngeal nerve. This was running with the superior thyroid atria and it supplies the cricothyroid muscle. It also supplies the inferior constrictor and we can see the external laryngeal nerve is a branch of superior laryngeal nerve. It is coming from the vagus and I will lift it up now. This is the superior laryngeal nerve. It is coming from the vagus. This is the vagus. This is the vagus and the superior laryngeal nerve is dividing into an internal laryngeal which is going into the thyroid head membrane and the external laryngeal nerve will supply the cricothyroid muscle. Therefore, to reiterate what I had mentioned earlier, when we are ligating the superior thyroid atria, we have to be very careful not to injure the external laryngeal nerve. The next structure that I will show you is the recurrent laryngeal nerve. This is the recurrent laryngeal nerve and we can clearly see it is running from below. So, let me show you the origin of the recurrent laryngeal nerve. This, as I had mentioned, is the vagus. We can see the vagus is crossing the subclavian artery and it is going further down and as it goes down, if you look very carefully, you will see it is giving a branch here which I have lifted up. This is the recurrent laryngeal nerve. The recurrent laryngeal nerve, it goes under the subclavian artery and we can see that here and then it runs up and this is what we are seeing here. This is the recurrent laryngeal nerve. It is a branch of the vagus. It enters into the larynx behind the cricothyroid joint. This supplies the inferior and the middle laryngeal constrictor. It also supplies the upper one third of the subclavius, but most importantly the recurrent laryngeal nerve. Once it enters into the larynx, it breaks up into an anterior and posterior division which supplies all the remaining muscles of larynx and it also supplies sensation to the larynx below the vocal cord. So, therefore, when we are ligating the inferior thyroid artery which is visible here, during thyroectomy, we have to be very careful not to injure the recurrent laryngeal nerve. So, these are the two important neurovascular relationships of the thyroid that I want to show you in Cy2 in another specimen. So, these are the points which I wanted to show to you about the thyroid gland in relation to its neurovascular structures and its blood supply. Thank you very much for watching. Dr. Sanyo Sanyal signing out. If you have any questions or comments, please put them in the comment section below. Mr. Ken Rollcomber batch is the camera person. Please like and subscribe. Have a nice day.