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The thyroid gland is located in the front of the neck at the level of the collarbone. It produces hormones that regulate the body's metabolism, bone growth, and heat production. Thyroid nodules are also called thyroid tumors.
Benign Thyroid Nodules
More than 95% of thyroid nodules are benign (non-cancerous), but tests are needed to determine if a nodule is cancerous. Benign nodules include several types:
Multinodular goiter, is also called a nontoxic goiter. A goiter means the thyroid gland has grown too large. This usually happens when the pituitary gland (in the brain) creates too much thyroid stimulating hormone (TSH). If the goiter is small, the problem may be treated with thyroid hormone pills. Surgery is needed if the goiter is large or does not stop growing after taking thyroid hormones. A large thyroid gland can press against the trachea (windpipe) or esophagus (food tube) and cause difficult breathing or eating.
Chronic thyroiditis (Hashimoto's disease) is an inflammation of the thyroid gland that develops slowly. It frequently leads to a decreased function of the thyroid (hypothyroidism). Middle-aged women are most commonly affected. Thyroditis occurs when the body's own immune system destroys the cells in the thyroid gland. Chronic thyroiditis is most common in women and people with a family history of thyroid disease.
Thyroid cysts are nodules filled with fluid. They can be small or large and might appear suddenly. If a nodule has both fluid and solid parts, it is called a complex nodule. They need to be surgically removed if they cause neck pain or difficultly swallowing.
Benign follicular adenomas. The word follicular means the cells look like a group of small circles under a microscope. If the follicular cells are contained within the nodule, the condition is called benign. If the cells have invaded the surrounding tissue, the diagnosis is cancer. The nodule must be surgically removed and examined under a microscope to look for evidence of invasion into the normal thyroid tissue or blood vessels.
A biopsy is needed to determine if a nodule is benign or cancerous. Your doctor may just watch a benign nodule too see if it grows or causes symptoms. If it grows larger, you might need another biopsy. Thyroid hormones can suppress the activity of the gland so that it does not develop more nodules.
Every year 20,000 new cases of thyroid cancer are diagnosed in the United States. Women are three times more likely to have thyroid cancer than men. Thyroid cancer is most common after 30, but it can develop at any age.
There are four types of thyroid cancer tumors:
Papillary tumors account for 78% of thyroid cancers. They often spread to lymph glands in the neck (metastasis), but rarely spread to distant organs. The lungs and bones are the most common sites of metastasis.
Follicular (Hurthle cell) tumors are the second most common thyroid cancer. Metastasis to distant organs, (lungs, bones, brain, liver, bladder, skin) is common. Metastasis to the lymph glands is less common than in papillary tumors. Follicular tumors usually develop during 40-60 years of age. They occur three times more often in women than men. The cure rate is 97% or better if treated correctly.
Medullary tumors. Metastasis to the lymph nodes occurs in the early stage of the tumor. After surgery, the hormone calcitoin is measured every 4-6 months to check for recurrence of the disease. The survival rate is 90% if the disease has not spread outside of the thyroid gland. Survival is 70% if disease has spread to lymph glands in the neck, and 20% if the disease has spread to distant organs.
Anaplastic cancer is the least common type of thyroid cancer, but the most dangerous. Three years after diagnosis and treatment, only 10% of patients are alive. More than 90% of anaplastic cancers spread to the lymph glands in the neck and distant organs. The tumors grow rapidly. The average age of onset is 65 years of age and older.Men are two times more likely than women to have anaplastic cancer. Many patients require a tracheotomy (breathing tube placed into the neck) because the tumor presses against the trachea and inhibits breathing. This cancer must be detected early. The cure rate is very low.
Most thyroid nodules cause no symptoms, but sometimes the person or a family member might see or feel a lump in the front of the neck.
The lump may cause pain or difficulty swallowing. If the nodule is creating an excessive amount of thyroid hormone, the person might feel heat intolerance, palpitations, fast heart beat, nervousness, insomnia, increased bowel movements, absent periods, fatigue, weight loss, hair loss or muscle weakness.
Causes and Risk Factors
The exact reason nodules grow in the thyroid gland is not known. But these factors increase the risk:
- Heredity. If a parent or sibling had a thyroid nodule, the chance of developing a nodule is increased.
- Age. The risk of developing a nodules increases as you age.
- Gender. Woman develop nodule more often than men.
- Thyroiditis. Nodules are more likely to form in people who have chronic inflammation of the thyroid gland.
- Radiation exposure to the head or neck. In the 1940s and 1950s, many babies, children, and teenagers were treated with radiation for acne and enlarged tonsils. People who had these treatments have an increased risk.
- Exposure to nuclear power plant accidents, or radioactive particles released into the air during atomic weapons testing also increases the risk.
A combination of symptoms, medical history, physical exams, and tests are used to determine a diagnosis. Thyroid nodules are often found during a routine physical examination. Your doctor might feel an abnormal lump on the front of your neck.
The TSH blood test measures a pituitary gland hormone that stimulates the thyroid gland. If the TSH level is increased, the thyroid gland may not be functioning properly. Additional blood tests are needed to measure other thyroid hormones. Both pituitary and thyroid tests are required to confirm that the problem is located in the thyroid gland.
T4 by RIA, T3 by RIA, and Thyroid Binding Globulin are blood tests used to measure the other thyroid hormones.
A thyroid scan measures the amount of iodine the thyroid can absorb.
Fine Needle Aspiration Biopsy. A needle is placed into the thyroid nodule; the cells are aspirated, and then examined under a microscope to determine if a nodule is cancerous.
Thyroid Ultrasound uses painless sound waves to create an image of the thyroid gland and identify nodules. Ultrasound can show if a nodule is solid or a fluid-filled cyst, but it cannot determine if a nodule is benign or malignant.
Thyroid Surgery and Treatments
Thyroid tumors require surgical removal of part or all of the thyroid gland (thyroidectomy). During a thyroidectomy, the surgeon might remove all of the thyroid gland or only the part that is diseased.
Radioactive Iodine treatments are given to most patients with thyroid cancer after the tumor is removed.
The laryngeal nerve (voice box nerve) is close to the site of surgery. After the operation, swelling of the nerve might cause weakness or paralysis of the vocal cords. But this is not common and rarely permanent.
Intraoperative Recurrent Laryngeal Nerve Monitoring is the latest technological tool used to prevent damage to the laryngeal nerve during surgery. Electrodes are placed near the muscles of the vocal cords and attached to a computer. The laryngeal nerve is monitored continually. If the nerve is inadvertently disturbed, the technician will alert the surgeon.
- This operation is used for thyroid cancer and large non-cancerous tumors.
- After surgery, patients must take a thyroid hormone pill every day.
Low blood calcium levels (hypocalcemia) may occur when the entire thyroid gland is removed. This condition is usually temporary, but may require calcium supplements. Permanent hypocalcemia is rare.
One side (a lobe) of the thyroid gland is removed. This operation is used if only one nodule is found in the thyroid gland.
Thyroid Lobectomy with Isthmusectomy
The removal of a thyroid lobe and the part that connects the two lobes (the isthmus). More thyroid tissue is removed than in a lobectomy.
After surgery, radioactive iodine is used to eliminate any thyroid cells that might be hidden in the body or could not be removed during the operation.
A single radioactive iodine pill is taken four to six weeks after the thyroid operation. The remaining thyroid cells will absorb the radioactive iodine and be eliminated.
Thyroid cells are the only cells able to absorb iodine, so the iodine pill will not harm any other cells in the body. Radioactive iodine causes no hair loss and no nausea.