The lateral lobes of the thyroid gland through the fascial capsule with lateral surfaces are in contact with the fascial sheaths of the common carotid arteries. 

The posterior surfaces of the lateral thyroid glands are adjacent to the larynx, trachea, tracheoesophageal sulcus, and also to the esophagus, and therefore, with an increase in the lateral thyroid glands, it can be compressed. In the interval between the trachea and esophagus on the right and on the front wall of the esophagus on the left, the recurrent laryngeal nerves rise to the cricothyroid ligament. These nerves, unlike near the thyroid glands, lie outside the fascial capsule of the thyroid gland.  

Thus, the area on the posterior surface of the lateral thyroid lobe constitutes the “danger zone” of the thyroid gland , to which the branches of the lower thyroid artery, which intersect here with the recurrent laryngeal nerve, are located, and the parathyroid glands are located nearby.   

With compression n. laryngeus recurrens or when the inflammatory process goes from the gland to this nerve, the voice becomes hoarse (dysphonia).

Thyroid blood supply. Thyroid vessels.

Blood supply to the thyroid gland is carried out by two upper thyroid (from the external carotid arteries) and two lower thyroid (from the thyroid trunks of the subclavian arteries) arteries. In 6-8% of cases, the unpaired lower thyroid artery takes part in the blood supply to the gland, a. thyroidea ima, extending from the brachiocephalic trunk. The artery rises to the lower edge of the isthmus of the thyroid gland in the tissue of the previsceral space, which should be remembered when conducting a lower tracheotomy. 

Superior thyroid artery , a. thyroidea superior blood supply to the upper poles of the lateral lobes and the upper edge of the isthmus of the thyroid gland.

Lower thyroid artery , a. thyroidea inferior departs from truncus thyrocervicalis in the ladder-vertebral space and rises under the 5th fascia of the neck along the anterior scalene muscle up to level VI of the cervical vertebra, forming a loop or arc here. Then it goes down and inside, perforating the 4th fascia, to the lower third of the posterior surface of the lateral lobe of the gland. The ascending part of the lower thyroid artery goes inward from the phrenic nerve. At the posterior surface of the lateral thyroid lobe, branches of the lower thyroid artery cross the recurrent laryngeal nerve, being anterior or posterior to it, and sometimes encompass the nerve in the form of a vascular loop.

The thyroid gland is surrounded by a well-developed venous plexus located between the fibrous and fascial capsules (Fig. 6.16). 

From it, through the superior thyroid veins accompanying the arteries, blood flows into the facial vein or directly into the internal jugular vein. The inferior thyroid veins are formed from the venous plexus on the anterior surface of the gland, as well as from the unpaired venous plexus, plexus thyroideus impar, located at the lower edge of the isthmus of the thyroid gland and in front of the trachea, and flow into the right and left brachiocephalic veins, respectively. 

Thyroid innervation. Thyroid nerves.

The innervation of the thyroid gland is carried out by the branches of the sympathetic trunk, upper and recurrent laryngeal nerves. 

Lymphatic drainage from the thyroid gland occurs in the pre-tracheal and paratracheal lymph nodes, and then in the deep lymph nodes of the neck.