The thyroid gland is an important endocrine organ responsible for growth and development of the body affecting all types of metabolic reactions and determining the body's response to external effects. Pathology of the thyroid gland is perhaps the most widespread among human diseases. According to WHO, about 500 million people worldwide suffer from various disorders of the thyroid gland. In some parts of the world, thyroid pathology is so common that it acquires social character.
Brief anatomical and physiological data. The thyroid gland consists of two lobes and an isthmus located at the front of the neck at the level of the fourth to sixth tracheal rings. In approximately 15% of cases there is a pyramidal lobe extending from the isthmus of the gland. The thyroid gland is covered with two layers of the neck fascia, of which the inner one is tightly connected with the glandular tissue, and the outer one lies quite freely. Blood vessels pass between the fascia layers to the gland tissue. The thyroid gland is very well supplied with blood from four fairly large vessels: two upper and two lower thyroid arteries. The upper thyroid arteries extend from the external carotid arteries, and the lower ones go from the innominate arteries, but sometimes they extend from the aortic arch. In approximately 18% of cases, there is an unpaired thyroid artery extending directly from the aorta. All this provides sufficient blood supply to the gland and can be accompanied with the risk of massive bleeding during operations on this organ. Five times more blood flows through a cubic centimeter of the thyroid tissue per unit time than through the kidney tissue of similar size.
The thyroid gland is located in close proximity to the vital formations of the neck (Fig. 5.1, 5.2, a, see color insert). Both lobes cover the trachea from the sides, and the isthmus is located at its front. From the sides, the neurovascular bundle of the neck adjoins the thyroid gland. The neurovascular bundle consists of the common carotid artery, the internal jugular vein and the vagus nerve (X pair of the cranial nerves). All of these formations can be damaged during surgical interventions on the gland. In the back of the lateral lobes of the thyroid gland are paired parathyroid glands. A person can have from 4 to 14 of them, they lie above and below the lateral lobes of the gland or at their level (Fig. 5.2, b, see color insert). In the furrow between the trachea and the esophagus, behind the trachea, the inferior laryngeal nerve (n. laringeus inferior) passes, innervating all the muscles of the larynx including the m. vocale, a muscle that strains the glottis during phonation.