Enlargement of the thyroid gland, causing a prominent swelling in the front of the neck. The thyroid normally weighs 0.5 to 0.9 oz (15 to 25 g); however, goitrous thyroid glands can grow to more than 2 lbs (1,000 g). A large goitre may interfere with breathing and swallowing and cause a choking feeling. Endemic goitre, the most common, is due to iodine deficiency, which causes a reduction in thyroid hormone synthesis (hypothyroidism). As a result, there is a compensatory increase in secretion of the anterior pituitary hormone thyrotropin. Thyrotropin not only stimulates thyroid hormone production but also causes an increase in size and number of cells in the thyroid. Advanced cases are treated with thyroid hormone or with surgical removal of the thyroid if it obstructs breathing. There are numerous other causes of goitre, including defects in thyroid hormone synthesis and inflammation of the thyroid. An enlarged thyroid may have normally functioning tissue or may produce too much hormone (hyperthyroidism). See also Graves disease.
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