Thyroid. Topography of the thyroid gland. The borders of the thyroid gland. The structure of the thyroid gland. Thyroid capsule. Lobes of the thyroid gland

The thyroid gland is located below the hyoid bone and is closely connected with the thyroid and cricoid cartilages. It consists of two lobes and an isthmus lying on the first rings of the trachea. 

The following layers cover the front of the thyroid gland : skin, subcutaneous adipose tissue, superficial fascia and platysma, superficial plate (2nd fascia) and pre-tracheal plate (3rd fascia) of the fascia of the neck with sublingual muscles. Of these, m is superficial. sternohyoideus, m. sternothyroideus. The upper poles of the lateral lobes are covered by the upper abdomen m. omohyoideus. A thickening of the pre-tracheal plate of the fascia of the neck (3rd fascia), fixing the gland to the thyroid, cricoid cartilage and trachea, is called the ligament supporting the thyroid gland, lig. suspensorium glandulae thyroideae [Berry]. 

Following the muscles and the 3rd fascia, the parietal plate of the 4th fascia is fused with it. In the midline of the neck, the 2nd one also grows with these fasciae, as a result of which a white line of the neck is formed, through which you can approach the thyroid gland without dissecting the sublingual muscles.

Behind the parietal leaf of the 4th fascia lies a spatium previscerale , bounded posteriorly by the visceral leaf of the 4th fascia. 

The visceral leaf forms a fascial, or external, capsule of the thyroid gland , surrounding it on all sides. 

Under the fascial capsule of the thyroid gland there is a layer of loose fiber surrounding the gland, through which the vessels and nerves approach it. The fascial capsule has no close connection with the gland, therefore, after its dissection, you can move (dislocate) the thyroid lobe. 

The thyroid gland has another capsule – fibrous, capsula fibrosa, or internal. This capsule is closely connected with the parenchyma of the gland, giving back inside the septum. Between fascial and fibrous capsules on the posterior surface of the thyroid gland are parathyroid glands. 

The upper poles of the lateral thyroid glands reach the middle of the height of the plates of the thyroid cartilage. The lower poles of the lateral lobes of the thyroid gland descend below the isthmus and reach the level of the fifth to sixth rings, not reaching 2–2.5 cm before cutting the sternum.  

In 1/3 of cases there is a pyramidal lobe of the thyroid gland , lobus pyramidalis [Lallouette], and sometimes additional thyroid lobes. The pyramidal lobe rises up from the isthmus or from one of the lateral lobes. 

The isthmus of the thyroid gland lies in front of the trachea (at a level from the first to the third or from the second to fourth of its cartilage). In relation to the isthmus, the name of the tracheotomy (dissection of the trachea) is determined: if it is made above the isthmus, then it is called upper, if lower – lower. Sometimes the isthmus of the thyroid gland is absent. 

You Might Also Like

Leave a Reply

Your email address will not be published. Required fields are marked *