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Publisher Summary This chapter discusses the medical aspects of thyroid disease. The thyroid gland is situated in the anterior aspect of the neck and consists of two lobes connected by a central isthmus approximately at the level of the cricoid cartilage. The adult thyroid weighs 15–20 g. It is derived embryologically as an epithelial proliferation from the floor of the pharynx, which migrates downwards anterior to the foregut before reaching its final position in front of the trachea by the seventh week. During migration, the gland remains connected to the floor of the pharynx by the thyroglossal duct, which subsequently disappears. The failure of resolution of the thyroglossal duct or persistence of thyroid remnants along its course may result in a thyroglossal cyst, fistula, or aberrant thyroid tissue. Thyroid hormones are not produced in the fetal thyroid until the twelfth week of gestation. Graves' disease is the most common cause of thyrotoxicosis, being about five times more frequent in females than in males; although it may develop at any age, it has a peak incidence at 20–40 years. The natural history of the untreated disease is one of remissions and exacerbations over many years. |
