Mediastinum

Because the thyroid gland is a hormone secreting organ, it is highly vascularized. It receives its blood supply from thesuperiorandinferior thyroid arteries. These arteries lie between the fibrous capsule and the pretracheal layer of deep cervical fascia.The superior thyroid artery is the first branch of the external carotid artery and supplies the top half of the thyroid gland. It divides into anterior and posterior branches supplying respective sides of the thyroid. On the anterior side, the right and left branches anastomose with each other. On the posterior side, the right and left branches anastomose with their respective inferior thyroid arteries.The inferior thyroid artery supplies the lower half of the thyroid and is the major branch of the thyrocervical trunk, which comes off the subclavian artery. It too divides into several branches, supplying the inferior portion of the thyroid and anastomosing posteriorly with the superior thyroid branches.There are three main veins that drain the venous plexus on the anterior surface of the thyroid. They include thesuperior, middle,andinferior thyroid veins, and each drains its respective portion of the thyroid. The superior and middle thyroid veins drain into the internal jugular veins, whereas the inferior thyroid vein drains into the brachiocephalic veins, behind the manubrium of the sternum.Lymphatic drainage of the thyroid gland is quite extensive and flows multidirectionally. Immediate drainage flows first to theperiglandular nodes, then to theprelaryngeal (Delphian), pretracheal,andparatracheal nodesalong the recurrent laryngeal nerve, and then tomediastinal lymph nodes.The principal innervation of the thyroid gland is derived from thesuperior, middle,andinferior cervical sympathetic gangliaof the autonomic nervous system andparasympathetic fibersfrom thevagus nerves. These nerves reach the thyroid gland by coursing with the blood vessels (superior and inferior thyroid periarterial plexuses).Dissection ConsiderationsCephalad to the superior pole of the thyroid gland, the external branch of thesuperior laryngeal nerveruns alongside the superior thyroid artery before turning medially to supply the cricothyroid muscle. High ligation of the superior thyroid artery during thyroidectomy places this nerve at risk of inadvertent injury, which would produce dysphonia by altering pitch regulation.

Thecricothyroid arteryis a potentially bothersome branch of the superior thyroid artery, which runs cephalad to the upper pole of the thyroid gland and runs toward the midline on the cricothyroid ligament. This vessel can be lacerated during emergent cricothyroidotomy.The inferior thyroid artery is closely associated with therecurrent laryngeal nerve. This nerve can be found after it emerges from the superior thoracic outlet, in a triangle bounded laterally by the common carotid artery, medially by the trachea, and superiorly by the thyroid lobe. The relationship of the recurrent laryngeal nerve and the inferior thyroid artery is highly variable in that the nerve can lie deep to the artery, superficial to the artery, or between the branches of the artery, and be different on either side of the neck. Consideration of this nerve and its branches must be given during dissection and thyroidectomy.ArteriesSuperior and inferior thyroid arteries

VeinsSuperior, middle, and inferior thyroid veins

LymphaticsPeriglandular, prelaryngeal, pretracheal, and paratracheal lymph nodes

NervesSympathetic: Superior, middle, and inferior sympathetic ganglia

Parasympathetic: Vagus nerves