The Thyroid Gland

Centar za stitastu zlezdu

Thyroid gland hormones affect growth and maturation, increase protein synthesis, accelerate fat decomposition and play a key role in the development of the central nervous system.  Problems arise when the thyroid gland produces too much hormone or not enough.

The thyroid gland is the largest endocrine gland in the body. It has the appearance of a shield or a butterfly and is located at the front of the neck, in front of the trachea between the cricoid cartilage and suprasternal pit. The thyroid gland produces and secretes the hormones thyroxine (T4) and T3, which regulate the metabolism of other tissues in the body. Para-follicular cells secrete Thyroid gland hormone calcitonin, which is involved in calcium homeostasis in the body.

Every cell and tissue in our body depends on thyroid hormones. The thyroid gland hormones affect growth and maturation, increase basal oxygen consumption and heat generation, increase protein synthesis, increase the minute volume of the heart, accelerate the breakdown of fats and decrease the amount of fat in the body. Thyroid hormones play a key role in the development of the central nervous system, promote awareness, increase sensitivity to different stimuli, and affect hunger, memory and learning ability, as well as the normal emotional tone. They also have an important role in the reproduction of men and women and the maintenance of normal pregnancy.

They affect growth and brain development in the fetal period and the first years of life. Thyroid hormone deficiency during this period can lead to mental retardation (cretinism). Cancer of the thyroid gland is manifested as a node in the thyroid gland or as a goiter (an enlarged thyroid gland). Malignant tumors of the thyroid gland are most commonly carcinomas, but they can be lymphomas as well, and it is not unusual that metastases of other tumors (breast, kidney, lung, esophagus, colon and melanoma) go to the thyroid.

Papillary carcinoma is the most common cancer of the thyroid gland. It occurs among young people in the second and third decade and the elderly (rarely in the middle-aged). It is more common in women. It appears as a painless node that is slow growing. The node, which is less than 2cm, promises an excellent prognosis.  Metastasis is often to the neck lymph nodes and sometimes to the lungs, brain and bones. Radioactive iodine is used for diagnosis and treatment.

Follicular carcinoma (carcinoma folicullare) usually occurs in older people, more frequently in women. There are different variations of this cancer, which show different invasiveness, but in general it has a relatively good prognosis. Smaller tumors have a better prognosis. Follicular carcinoma most commonly shows metastases in bone, lung and the brain. Metastases bind radioactive iodine, which is important for diagnosis and therapy. This carcinoma can create hormone imbalance of the thyroid gland and lead to thyrotoxicosis.

Anaplastic carcinoma (carcinoma anaplasticum) usually occurs after fifty years both in men and women. It is extremely invasive, and has a poor prognosis. This tumor grows quickly and penetrates into the trachea, esophagus, throat and neck.

Medullary thyroid carcinoma (carcinoma medullare) occurs in the elderly (in the sixth and seventh decade), more frequently in women. It has a worse prognosis than papillary and follicular, but better than anaplastic carcinoma. This tumor secretes calcitonin, which can be defined as a tumor marker (to be used for diagnosis). In this form of cancer and its metastases, calcium can be deposited, which is used for diagnosis.

Diagnosis

Sometimes cancer is in the form of a node, so the diagnosis has to be made by removing  the node so that it can be examined under the microscope. During scintigraphy, which is a technique whereby a radioactive drink is taken and a picture is then taken to see where the radiation has been concentrated. Carcinoma is often portrayed as a cold node. Thyroid hormones are often increased, but it is not essential for the diagnosis, because they may be increased in cases of goiter. The monitoring of these hormones is important after surgery. The diagnosis can be definitely established by histology obtained by puncture of the thyroid with a fine needle. Puncture is simple and painless and is repeated if the findings are not entirely clear.

Therapy

The treatment is usually surgical and consists of removing the greater part of the thyroid gland. After the operation thyroxine has to be given for life.  It prevents the pituitary hormone (TSH), which stimulates the thyroid gland and can lead to tumor regrowth. The rest of the thyroid gland and eventual metastasis can be destroyed with radioactive iodine. Further prognosis depends on the type of cancer, its size and the extent to which it has metastasized.