Thyroid Glands – Tissue and Systems

Thyroid Glands – Tissue and Systems

This article describes the basic anatomy and function of the thyroid gland. An understanding of the basic form and physiology of the thyroid gland will allow better recognition of a possible thyroid cancer. Thyroid cancer is rare and account for less than 1% of all cancers in the United States. It is still important to consider because the majority of thyroid cancers are quite treatable and even curable if detected early enough. This emphasizes the importance of recognizing symptoms that should prompt investigation with possible diagnosis. Early diagnosis and treatment, as with the vast majority of cancers, will provide the best possible outcomes.

The thyroid gland is a small endocrine organ that sits in the front of the neck. The name thyroid comes from a Greek word meaning shield. The thyroid gland looks a bit like an ancient shield or perhaps like a butterfly with two wings and two tips on each wing. The thyroid gland uses iodine and proteins from the diet to make thyroid hormone. The hormone is secreted in two major forms, T3 and T4 also known commonly as thyroxines. The thyroid hormone is also regulated by the brain as it secretes a thyroid stimulating hormone (TSH) to cause the gland to be more active. This mechanism functions like a thermostat or simple feedback loop. When the thyroid hormones become low, the brain makes more TSH to counterbalance this and vice versa.

Thyroid hormone controls many aspects of metabolism, calories used and body temperature. Abnormalities in the level of thyroid hormone can thus cause changes that affect the entire body. Thyroid cancer typically does not impact the levels of thyroid hormone. Hormone level s becomes relevant when the part or the entire thyroid must be removed to treat a thyroid cancer. In these situations the thyroid hormone levels must be regulated with medications and blood level monitoring.

Other diseases not involving cancer more commonly affect the thyroid gland. An underactive thyroid gland is also known as hypothyroidism. An enlarged gland is known as a goiter. An overactive thyroid gland creates hyperthyroidism. These situations typically do not involve cancer expect for goiter rarely being associated with lymphoma of the thyroid gland.

The thyroid is supplied by arteries from the lower neck and veins in the same area. The nerve that controls the vocal cords and pitch of the voice run very close to the thyroid gland. Cancers of the thyroid that invade these nerves may cause hoarseness or changes in the voice. Treatment of thyroid cancer often involves surgery to remove part of the thyroid gland. During removal of the gland, these crucial nerves (i.e. recurrent laryngeal nerve and superior laryngeal nerves) are at risk of injury. At each corner of the thyroid gland, there is normally an adjacent gland known as the parathyroid gland. The parathyroid gland is responsible for controlling calcium levels in the body. These glands share a common blood supply with the thyroid gland and are often very close to each other. During treatment for thyroid cancer, these glands are at risk for injury or inadvertent removal.

A healthy thyroid should be smooth, without nodules and make adequate amounts of thyroid hormone for proper metabolism. Any defects in these might indicate disease of thyroid or even thyroid cancer. One of the commonest conditions noticed about the thyroid will be a slight enlargement of it. Enlargement of the thyroid is known as goiter. Most goiters are related to mild hypothyroidism. A nodule or small bump on the thyroid gland is abnormal. When these nodules are felt, it should be brought to the attention of your doctor for further investigation.

A risk factor for the development of thyroid cancer is radiation to the neck. This may have occurred when children in the past had cancer in the neck (like cancer of the thymus) treated with radiation therapy. The medical profession is much more careful to limit radiation to the thyroid now as these cancers have appeared over time. If you have an x-ray, even a dental x-ray, you should have a shield over your thyroid.

Radiation from a nuclear accident can cause thyroid cancer. In the United States, if you live 10 miles or less from a nuclear reactor, you can get potassium iodide tablets to keep on hand. Should an accident occur, taking the potassium iodide protects the thyroid from the effects of radiation.

If you have been exposed to radiation of the neck for cancer treatment, or you have any reason to think you were in an area of a nuclear accident, make sure any lumps in the area of the thyroid are checked quickly.

There are several ways to assess the health and function of the thyroid gland. Having symptoms of abnormal thyroid function is a signal that thyroid hormone levels may need to be checked. Very sensitive blood work can check the level of thyroxine as well as the level of thyroid stimulating hormone. A normal thyroid stimulating hormone (TSH) virtually excludes abnormalities of thyroid hormone production. Examination of the thyroid gland can often detect problems such as tenderness, enlargement, nodules or possible spread to lymph nodes in the neck. When enlargement or possible nodule is felt some type of imaging is needed to better define the anatomy. An ultrasound of the neck is the simplest and safest way to image the thyroid. Any nodules or tumors within the thyroid gland can be seen with the ultrasound. The ultrasound can also be used to guide biopsy of possible cancer. A biopsy is a sampling of cells for examination under the microscope to look for cancer cells. This is usually done with a fine gauge needle. Sometimes this sampling is helpful if it is entirely normal or if it shows cancer, either way it gives a definitive answer. The sampling sometimes is inconclusive and may lead to surgical removal for the suspicion of cancer.

There are several different kinds of thyroid cancer:

  • Papillary thyroid cancer (the most common thyroid cancer and has the best prognosis)
  • Follicular thyroid cancer
  • Hurthle cell cancer
  • Anaplastic Cancer
  • Lymphoma of the thyroid
  • Medullary thyroid cancer

The commonest types (papillary and follicular variants) carry a good prognosis compared with most cancers and are often curable. Importantly, symptoms of thyroid cancer should not be ignored and should be brought to the attention of your doctor for further investigation.

REFERENCES:

  1. www.ncbi.nlm.nih.gov/pubmedhealth/PMH0002193/
  2. www.cancer.gov/cancertopics/types/thyroid
  3. Townsend Jr, CM; Beauchamp RD; Evers BM; Mattox KL. (2008) Townsend: Sabiston Textbook of Surgery, 18th ed. Chapter36 . New York, NY: Saunders.
  4. Cameron JL; Cameron AM. (2010) Cameron: Current Surgical Therapy, 10th ed. Chapter 602. Philadelphia, PA: Elsevier Saunders
  5. This article was originally published on September 3, 2012 and last revision and update was 9/4/2015.