 This is a demonstration of the thyroid gland with its neuro vascular relationships. So we have completely reflected all the strap muscles. The only one which is visible here is the thyrohyoid muscle on this side and the thyrohyoid muscle on that side. And we can see a little bit of the cricothyroid muscle on either side. This is the thyroid gland in front of us. So this is the right lobe of the thyroid, eastmus, left lobe of the thyroid. This is the upper pole and this is the lower pole. And this was where it was attached to the lower part of the thyroid cartilage, the cricoyed and it was attached to the upper part of the trachea. This was covered by the pre tracheal fascia which has been removed. And the pre tracheal fascia is the one which is continuous with the fascia of the trachea and it goes up to the higher bone. So this has been removed and this has been reflected to show the structures on the under surface of the thyroid gland also. First let's take a look at the relationship of the thyroid gland. Personally the thyroid is related to the second, third and fourth tracheal rings and we can see the tracheal rings here. So when we are doing a tracheostomy we have to cut the isthmus of the thyroid gland as a part of the tracheostomy process and only then we can make an opening in the trachea. The lobes of the thyroid gland are related not only to the trachea but behind the trachea is the isophagus which we cannot see here and it is also related to this artery which we have detected laterally this is the common carotid artery and further laterally is the internal jugular vein which also has been retracted. So these are also important posterior lateral relationships of the lobes of the thyroid gland and also running in the carotid sheath is this big nerve. This is the vagus nerve. So this is also an important posterior lateral relationship of the thyroid gland. All these have been retracted just to get a close view. Now let's take a look at the neurovascular structures which are important not only from the functional point of view but also from the surgical point of view. Let's take a look at this artery here. This is the first branch anterior branch from the external carotid. This is the external carotid which I have lifted up here and we can see this branch coming down. This is the superior thyroid artery. The superior thyroid artery and it enters the superior pole of the thyroid gland and it supplies the anterior superior and lateral aspect of the thyroid gland. Not only that, this is accompanied by this nerve here. This is the external laryngeal nerve. The external laryngeal nerve is the smaller terminal division of the superior laryngeal nerve and this external laryngeal nerve runs in close proximity with the superior thyroid artery as you can see very clearly and it supplies the cricothyroid muscle and the inferior pharyngeal constrictor. This is a part of the inferior pharyngeal constrictor here. So the importance of this artery is that when we are doing a thyroidectomy and we have to ligate the superior thyroid artery, if we ligate it far away like this, we are liable to catch the external laryngeal nerve and injure it. Therefore we have to ligate the superior thyroid artery as close to the thyroid gland as possible and this is the approximate place where we ligated. That way the external laryngeal nerve is bypassed. If we injure the external laryngeal nerve then we could produce paralysis of the cricothyroid and the cricothyroid is the tensor of the vocal cord so therefore the person will have weak voice. So that is one important point to be remembered about the arterial supply and its relationship. Now I will draw your attention to the next arterial supply of the thyroid gland for that I have retracted it here and we can see this artery here which I have lifted up. This is the first branch from the thyro-survival trunk. This is the inferior thyroid artery. The inferior thyroid artery it comes like this and sometimes it makes a loop or sometimes it goes directly and it enters the thyroid gland from its inferior pole and it goes in the posterior aspect of the thyroid gland and it supplies the inferior posterior and medial surface of the thyroid gland that is this surface and this is one of the main suppliers of the parathyroid gland also which is located on the inner surface. The inferior thyroid artery is in close proximity with this nerve here. This is the recurrent lanageal nerve. To show you the same thing on that side let me retract this thyroid gland a little this side. We are showing the same structures on the left side of the thyroid. We can see this is the recurrent lanageal nerve which I have lifted up and in close proximity is this inferior thyroid artery. So the importance of this proximity is that again when we are ligating the inferior thyroid artery if we try to ligate it close to the inferior pole we are likely to catch the recurrent lanageal nerve. To show the same thing here we can see how close it is to the recurrent lanageal nerve so if we try to catch the inferior thyroid artery close by we are able to catch both of them in our forces. So therefore while ligating the inferior thyroid artery we should be far away from the gland and therefore we usually choose somewhere in this region where it is far away. We usually ligate it here. That way we are sure that the recurrent lanageal nerve is spared. So the rule of the thumb is superior thyroid artery as close to the thyroid inferior thyroid artery as far from the thyroid should be ligated. So these are the two important arterial supply and the two important nerves which are accompanying them. If we inadvertently ensure the recurrent lanageal nerve on any one side the side vocal cord will be paralysed because the recurrent lanageal nerve supplies all the muscles of the bladder except the cricothyroid. And so therefore that side vocal cord will occupy what is known as a cadaveric position which is slightly medial to the paramedial resting position and when the person tries to speak one side vocal cord will move the other side will not move so the person will have what is known as hoarseness of voice. If both the sides are paralysed which is very rare but it may happen then the person will get both the vocal cords will be in a cadaveric position and they will be very close to each other and the person will have respiratory stridor. That means when he tries to inspire when the vocal cords need to move away they cannot move the person will have respiratory stridor and may even require an emergency tracheostomy. There is a condition called lignus thyroiditis where the whole thyroid is very hard and stony and it can compress the trachea and that can produce respiratory distress. In such situations we may have to do what is known as an Isthmusectomy we have to cut the Isthmus so that the compression is relieved. So that brings me to various surgical procedures that can be done on the thyroid without going into details. The most common illness which can afflict the thyroid is what is known as goiter which is a non-inflammatory, non-neoplastic enlargement of the thyroid gland. Depending on the location and the size of the goiter we can do what is known as either a lobectomy that is removing only one lobe or we can remove a lobe and part of the Isthmus that is known as heavy thyroidectomy. Then there is a condition called multinodular goiter where there are multiple goiter all over then we have to do what is known as a subtotal thyroidectomy and then we have cancer of the thyroid either papillary or follicular cancer then we have to do what is known as a near-total thyroidectomy. The near-total thyroidectomy is called so because the parathyroid glands are located behind and we have to save a little bit of the thyroid gland in this region so as to safeguard at least one parathyroid otherwise the person will have hypoglycemic tetanine. These are a few quick mention of the various surgical procedures which are very commonly performed in the thyroid gland. Thank you very much for watching. If you have any questions please put them in the comment section below. Thank you very much.