The thyroid gland is an H-shaped gland which lies in the front of the neck overlying the windpipe. It consists of a large lobe on each side, the lobes being connected by a narrow band called the isthmus. The entire gland is composed of numerous microscopic follicles which secrete the hormone thyroxine. This hormone is about 65 per cent iodine, and its chief function is to accelerate metabolism; it is necessary for normal growth and development.
A method of measuring the rate of the various chemical processes occurring in the body (metabolism) is by the BMR, or basal metabolic rate.
Insufficient production of the thyroid hormone in the young results in a condition known as cretinism; the cretin is an individual characterized by small stature, retarded mental development, and underdevelopment of the sexual organs. In adults, hypoactivity of the thyroid gland results in a condition known as myxedema; the individual is overweight, mentally and physically sluggish, with sparse hair and boggy tissues. In these conditions the rate of all the metabolic processes is slow. Marked improvement may be brought about by administering thyroid extract in these conditions of underactive thyroid gland.
Any abnormal enlargement of the thyroid gland is called a goiter. Such may be of normal function, or hypoactive or hyperactive. Simple goiter is a diffuse enlargement of the entire gland. It is due to a deficiency of iodine in the diet. The gland enlarges, apparently in attempts to mannfacture sufficient hormone. A prominent swelling in the neck occurs and may cause symptoms of pressure on the windpipe with shortness of breath or difficulty in swallowing. Often marked benefit may follow medical measures, but if the symptoms of pressure are pronounced, the excess of the gland may have to be removed surgically (subtotal thyroidectomy) .
Exophthalmic goiter, or toxic goiter, or hyperplastic goiter, is a diffuse enlargement of the thyroid gland with overgrowth of the follicles and overproduction of thyroxine. All the metabolic processes of the body are stimulated to overactivity. The patient loses weight; the pulse rate is increased; tremors develop; there is excess sweating and hot flashes; the eyes are pushed forward, a condition known as exophthalmos, or “pop-eyes”; apprehension and nervousness increase. As the disease progresses, weight loss continues and the patient becomes emaciated. Pressure symptoms from the enlarging gland may occur.
Treatment of this toxic goiter rests with surgical removal of most of the overactive gland tissue (subtotal thyroidectomy). The incision is made across the lower front of the neck and the thyroid exposed. The major portion of the lobes and the isthmus are excised, leaving only a small amount of gland tissue at the lower portion of the lobe on each side. Only a small amount of gland tissue is necessary for normal function, but the amount of gland that is excised is judged by the degree of overactivity. The incision is closed by plastic surgery technique for cosmetic reasons. In cases of severe overactivity of the thyroid, extensive and prolonged preoperative preparations may be necessary. This may include a period of absolute rest in a quiet atmosphere removed from disturbing noises and sights and avoiding all forms of apprehension; sedatives may be used, and drugs which suppress the thyroid gland’s activity may be needed in the preparation for surgery.
In the recent atomic years radioactive iodine has been used in the treatment of overactive thyroid. The gland is known to absorb and utilize iodine for the formation of its hormone. Iodine which has been rendered radioactive is given by mouth to be absorbed by the thyroid gland. Here it gives off rays which partially destroy the gland’s cells. The radioactivity is of short duration but the effect on the gland permanent. This is a therapeutic course of radioactive iodine, but the activity of the gland may be studied beforehand by a tracer dosage. For this test a small harmless amount of radioactive iodine is given and is absorbed by the thyroid gland; then the amount of radiation given off from the gland is measured by a recording instrument (such as the Geiger counter). This test is of accurate value in determining the magnitude of treatment necessary, either surgically or by radioactive iodine.
Adenomatous goiter, or nodular goiter, is a condition wherein a benign tumor develops in the gland to form a lump in the gland substance. Often these nodules are multiple. The gland may become overactive and the symptoms of toxic goiter ensue, but most are of normal activity.
In some cases, these benign nodules may undergo malignant change. Therefore the best treatment is surgical removal of the greater portion of the gland containing the tumor (subtotal thyroidectomy). This is particularly necessary in younger individuals since the chances of the benign nodule becoming cancerous are greater, as the life expectancy is longer with more years for possible malignant change.
Thyroidectomy (thyroid-out) may be of one lobe or both, and may be subtotal (partial) or total. In the case of cancer of the thyroid, obviously total thyroidectomy must be performed; x-ray may be employed.
Inflammation of the thyroid gland is called thyroiditis. It may be acute or chronic and symptoms of overactivity may occur. Treatment may be by medical means or with x-ray, and occasionally partial thyroidectomy is necessary.