Goiter

Goiter 

Definition

Goiter refers to any visible enlargement of the thyroid gland.

Description

The thyroid gland sits astride the trachea (windpipe) and is shaped like a butterfly. It makes thyroxin, a hormone that regulates the metabolic activity of the body, rather like the gas pedal on a car. Too much thyroxin increases the metabolism, causing weight loss, temperature elevation, nervousness, and irritability. Too little thyroxin slows the metabolism down, deepens the voice, causes weight gain and water retention, and retards growth and mental development in children. Both conditions also alter hair and skin growth, bowel function, and menstrual flow.

Curiously, the thyroid gland is often enlarged whether it is making too much hormone, too little, or sometimes even when it is functioning normally. The thyroid is controlled by the pituitary gland, which secretes thyroid stimulating hormone (TSH) in response to the amount of thyroxin it finds in the blood. TSH increases the amount of thyroxin secreted by the thyroid and also causes the thyroid gland to grow.

Causes and symptoms

Excess TSH (or similar hormones), cysts, and tumors will enlarge the thyroid gland. Of these, TSH enlarges the entire gland while cysts and tumors enlarge only a part of it.

The only symptom from a goiter is the large swelling just above the breast bone. Rarely, it may constrict the trachea (windpipe) or esophagus and cause difficulty breathing or swallowing. The rest of the symptoms come from thyroxin or the lack of it.

Diagnosis

The size, shape, and texture of the thyroid gland help the physician determine the cause. A battery of blood tests are required to verify the specific thyroid disease. Functional imaging studies using radioactive iodine determine how active the gland is and what it looks like.

Treatment

Goiters of all types will regress with treatment of the underlying condition. Dietary iodine may be all that is needed. However, if an iodine deficient thyroid that has grown in size to accommodate its deficiency is suddenly supplied an adequate amount of iodine, it could suddenly make large amounts of thyroxin and cause a thyroid storm, the equivalent of racing your car motor at top speed.

Hyperthyroidism can be treated with medications, therapeutic doses of radioactive iodine, or surgical reduction. Surgery is much less common now than it used to be because of progress in drugs and radiotherapy.

Prognosis

Although goiters diminish in size, the thyroid may not return to normal. Sometimes thyroid function does not return after treatment, but thyroxin is easy to take as a pill.

Prevention

Euthyroid goiter and hypothyroid goiter are common around the world because many regions have inadequate dietary iodine, including some places in the United States. International relief groups are providing iodized salt to many of these populations. Because mental retardation is a common result of hypothyroidism in children, this is an extremely important project.

Resources

Organizations

International Council for the Control of Iodine Deficiency Disorders. 43 Circuit Road, Chester Hill, MA, 02167. (207) 335-2221. 〈http://www.tulane.edu/∼icec/icciddhome.htm〉.

Micronutrient Initiative (c/o International Development Research Centre). 250 Albert St., Ottawa, Ontario, Canada K1G 3H9. (613) 236-6163, ext. 2050. 〈http://www.idrc.ca/mi/index.htm〉.

Key terms

Cyst — A liquid-filled structure developing abnormally in the body.

Euthyroid — Having the right amount of thyroxin stimulation.

Hyperthyroid — Having too much thyroxin stimulation.

Hypothyroid — Having too little thyroxin stimulation.

Pituitary gland — The master gland, located in the middle of the head, that controls most of the other glandss by secreting stimulating hormones.

Radiotherapy — The use of ionizing radiation, either as x rays or radioactive isotopes, to treat disease.

Thyroxin — The hormone secreted by the thyroid gland.

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goiter /goi·ter/ (goi´ter) enlargement of the thyroid gland, causing a swelling in the front part of the neck.goi´trous

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aberrant goiter  goiter of a supernumerary thyroid gland.

adenomatous goiter  that caused by adenoma or multiple colloid nodules of the thyroid gland.

Basedow's goiter  a colloid goiter which has become hyperfunctioning after administration of iodine.

colloid goiter  a large, soft goiter with distended spaces filled with colloid.

diffuse toxic goiter  Graves' disease.

diving goiter  one that is movable, sometimes above and sometimes below the sternal notch.

exophthalmic goiter  one accompanied by exophthalmos.

fibrous goiter  one in which the thyroid capsule and stroma are hyperplastic.

follicular goiter  parenchymatous g.

intrathoracic goiter  one in which a portion is in the thoracic cavity.

iodide goiter  that occurring in reaction to iodides at high concentrations, due to inhibition of iodide organification.

lingual goiter  enlargement of the upper end of the thyroglossal duct, forming a tumor at the posterior part of the dorsum of the tongue.

lymphadenoid goiter  Hashimoto's disease.

multinodular goiter  goiter with circumscribed nodules within the gland.

nontoxic goiter  that occurring sporadically and not associated with hyperthyroidism or hypothyroidism.

parenchymatous goiter  one marked by increase in follicles and proliferation of epithelium.

simple goiter  simple hyperplasia of the thyroid gland.

suffocative goiter  one which causes dyspnea by pressure.

wandering goiter  diving g.

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goi·ter (goitr)

n.

A noncancerous enlargement of the thyroid gland, visible as a swelling at the front of the neck, that is often associated with iodine deficiency.

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goitrous (-trs) adj.

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goiter,

n distended thyroid gland, usually manifested as a noticeable bulge in the neck.

Goiter.

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goiter (goi´tur),

n an enlargement of the thyroid gland.

goiter, colloid,

n (endemic goiter, iodine deficiency goiter, simple goiter) a visible enlargement of the thyroid gland without obvious signs of hypofunction or hyperfunction of the gland resulting from inadequate intake or from an increased demand for iodine.

goiter, endemic,

n See goiter, colloid.

goiter, exophthalmic,

n a disease of the thyroid gland consisting of hyperthyroidism, exophthalmos, and goiterous enlargement of the thyroid gland. A diffuse primary hyperplasia of the thyroid gland of obscure origin; may occur at any age. It produces nervousness, muscular weakness, heat intolerance, tremor, loss of weight, lid lag, and absence of winking and may lead to thyrotoxic heart disease and thyroid crisis.

goiter, iodine deficiency,

n See goiter, colloid.

goiter, nodular, nontoxic,

n the recurrent episodes of hyperplasia and involution of colloid goiter, which result in a multinodular goiter. Symptoms are related to pressure.

goiter, simple,

n See goiter, colloid.

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goiter, goitre

enlargement of the thyroid gland, causing a swelling in the front part of the neck.

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adenomatous goiter

multilobular goiters cause thyroid enlargement in cats.

colloid goiter

is characterized by the presence of a large soft thyroid gland with its glandular space distended with colloid. Most cases occur in neonatal lambs, calves and kids which show a high rate of stillbirths and weakness and a high mortality rate. Enlarged thyroid glands and alopecia are good indicants of the existence of a nutritional deficiency of iodine, the usual cause of goiter in animals.

dyshormonogenetic goiter

an impairment in thyroglobulin synthesis is thought to be the cause of inherited, congenital goiter recorded in sheep, cattle and goats. The thyroid gland is enlarged, there is a high neonatal mortality, a silky wool in sheep and a rough, sparse haircoat in goats. Called also inherited goiter.

goitrogen-induced goiter

there are a number of goitrogens in the environment of grazing animals. Their effect is almost entirely on the newborn. Common agents are low level intakes of cyanogenetic glycosides, e.g. in white clover, the glucosinolates in Brassica spp. plants, and mimosine in Leucaena leucocephala.

hyperplastic goiter

diffuse hyperplasia is the standard response to dietary iodine deficiency and to poisoning by plant goitrogens. It may also be caused by persistent exposure of the fetus to a high iodine intake of the dam. See also iodide goiter (below). Neonates are the usual subjects and the disease is manifested by clinical goiter, often sufficient to cause dystocia, and weak neonates with a high rate of stillbirths and deaths soon after birth.

inherited goiter

see dyshormonogenetic goiter (above).

iodide goiter

that occurring in reaction to iodides at high concentrations, due to inhibition of iodide organification.

nodular goiter

an endocrinologically inactive nodular enlargement of the thyroids in old dogs and horses. In old cats similar goiters sometimes develop functional adenomas.