Thyroid Gland

Where is the thyroid?
The thyroid is one of the body’s most significant glands. It is located low in the front of the neck, below the Adam’s apple. The gland is shaped like a butterfly and wraps around the windpipe or trachea. The two lobes or wings on either side of the windpipe are joined together by a bridge, called the isthmus, which crosses over the front of the windpipe.

What does it do?
The thyroid gland manufactures and stores thyroid hormones (TH), often referred to as the body’s metabolic hormone. TH stimulates enzymes that combine oxygen and glucose, a process that increases your basal metabolic rate (BMR) and body heat production. In essence, the hormone tells your body how fast to use energy. If there is too much TH in your blood, you can develop a condition known as hyperthyroidism, which is when your body uses energy too fast. If there is too little TH in your blood, you could develop hypothyroid and in that case, your body would use energy too slowly. The hormone also helps maintain blood pressure, regulates tissue growth and development and is crucial for skeletal and nervous system development. It also plays an important role in the development of the reproductive system.

Who is at risk?
About 13 million Americans—more of them women than men—are affected by a thyroid disease or disorder. Hyperthyroidism affects an estimated 2.6 million people in the United States, while hypothyroidism affects an estimated 9.6 million people in the U.S. These numbers could actually be much higher because well over half of the individuals with thyroid disease do not know they have it. Research shows that there is a strong genetic link between thyroid disease and other autoimmune diseases including certain types of diabetes, anemia and arthritis.
Women are five to eight times more likely to have thyroid dysfunction than men, but most don’t know they have it. Women often overlook their symptoms or mistake them for symptoms of other conditions. For example, women are at particularly high risk for developing thyroid disorders following childbirth. Symptoms such as fatigue and depression are common during this period, but these are also symptoms of thyroid disease. Postpartum thyroiditis occurs in 5  to 10 percent of women following childbirth. Thus, more than half of thyroid conditions remain undiagnosed, according to the Thyroid Foundation of America.

What can go wrong?
When your thyroid doesn’t work properly, it can cause you to feel nervous or tired, make your muscles weak, cause weight gain or loss, impair your memory, and affect your menstrual flow. A thyroid disorder can also cause miscarriage and infertility.

  • It can release too little TH, resulting in a condition known as hypothyroidism (under active thyroid).
  • It can release too much TH, resulting in a condition known as hyperthyroidism (overactive thyroid).
  • Its tissue can overgrow, resulting in a nodule, a small lump in part of the gland. Most nodules are harmless growths, but some are cancerous. In fact, according to the American Thyroid Association, about one in ten thyroid nodules are cancerous. The National Cancer Institute estimates that about one percent of all cancers diagnosed in the United States each year are thyroid cancers.

A bit more about Hypothyroidism:
When too little TH is released, the body’s metabolic rate decreases, and the body slows down. Hypothyroidism often goes undiagnosed because its symptoms are often mistaken for or attributed to other conditions. Symptoms include:

  • fatigue
  • depression
  • low body temperature
  • weight gain
  • dry or itchy skin
  • thin, dry hair/hair loss
  • puffy face, hands and feet
  • decreased taste and smell
  • slow heart rate
  • constipation
  • poor memory
  • trouble with concentration
  • hoarseness/husky voice
  • irregular or heavy menstruation
  • muscle aches
  • infertility
  • high cholesterol
  • goiter (enlarged thyroid gland)

A bit more on Hyperthyroidism:
When too much TH is released, the body’s metabolic rate increases, and your metabolism speeds up. Symptoms of hyperthyroidism include:

  • nervousness/irritability
  • weight loss
  • fast/irregular heart rate
  • heat intolerance/increased perspiration
  • changes in appetite
  • sleep disturbances (such as insomnia)
  • muscle weakness
  • trembling hands
  • more frequent bowel movements
  • shorter and scantier menstrual flow
  • exophthalmoses (bulging eyes)
  • goiter (enlarged thyroid gland)

Thyroid Nodules:
Ranging from as small as a millimeter to as large as several inches, thyroid nodules themselves don’t represent illness. In fact, it is estimated that one in ten Americans will develop a thyroid nodule at some point in their lives. Nodules do, however, indicate an underlying problem with the thyroid and should be evaluated if they are discovered.

The majority of nodules are benign discrete clumps of thyroid cells which don’t function like normal thyroid tissue. Other nodules may turn out to be simple cysts. There is a slight chance that a thyroid nodule is cancerous—about 10 percent of nodules are cancerous—so it is important to have a health care professional assess all growths.
While most nodules have no symptoms, are never detected and are harmless, some can be large enough to press against the windpipe and cause difficulty swallowing or can cause a cough. A nodule can also become overactive, suppressing the rest of the gland and causing hyperthyroidism.

A thyroid nodule can occur in any part of the gland. Some nodules can be felt quite easily, while others can be hidden deep in the thyroid tissue or located very low in the gland where they are difficult to feel.

What is the prevalence of thyroid nodules and cancer?
These days, with modern imaging studies such as ultrasound (US), computerized tomography (CT), and magnetic resonance imaging (MRI), more and more thyroid nodules are being found incidentally. This means the nodules are found during studies that are being done for reasons other than examination of the thyroid gland. It is estimated that 4-8% of adult women and 1-2% of adult men have thyroid nodules that can be felt on physical examination, but closer to 30% of women have nodules detectable by ultrasound. In fact, the diagnosis of a thyroid nodule is the most common endocrine problem in the United States.

Although the majority of thyroid nodules are benign (not cancerous), about 10% of nodules do contain cancer. Therefore, the primary purpose for evaluating a thyroid nodule is to determine whether cancer is present.

What are the symptoms of thyroid nodules?
The vast majority of thyroid nodules do not cause symptoms. However, if the cells in the nodules are functioning and producing thyroid hormones on their own, the nodule may produce signs and symptoms of too much thyroid hormone (hyperthyroidism). A small number of patients complain of pain at the site of the nodule that can travel to the ear or jaw. If the nodule is very large, it can compress the esophagus or trachea and cause difficultly swallowing or shortness of breath. In rare instances, a patient may complain of hoarseness or difficulty speaking because of compression of the larynx (or voice box).

What are the types of thyroid nodules?
Thyroid nodules may be single or multiple. A thyroid gland that contains multiple nodules is referred to as a multinodular goiter. If the nodule is filled with fluid or blood, it is called a thyroid cyst. If the nodule produces thyroid hormone in an uncontrolled manner without regard to the body’s needs, the nodule is referred to as autonomous. This type of nodule may cause signs and symptoms of too much thyroid hormone or hyperthyroidism, as mentioned above. Occasionally, patients with a thyroid nodule may have too little thyroid hormone or hypothyroidism.
The most common types of noncancerous, single thyroid nodules are colloid nodules or follicular adenomas. Another type of benign nodule that may be seen is called a Hurthle cell adenoma. Only a minority of nodules are cancerous. Cancerous nodules are classified by the types of malignant thyroid cells they contain. These cell types include papillary, follicular, medullary, or poorly differentiated (anaplastic) cells. The prognosis for the patient depends largely on the cell type and how far the cancer has spread by the time it is discovered.
In addition to thyroid cancer of the cell types mentioned, thyroid nodules may contain lymphoma, a cancer of the immune system. Cancer from other sites, such as breast and kidney, also can spread (metastasize) to the thyroid gland.
The cause of most thyroid nodules is not known. In certain cases, a lack of iodine in the diet can cause the thyroid gland to develop nodules. There also are certain genes that may be involved in the development of nodules in some individuals.

How are thyroid nodules diagnosed?
Thyroid nodules usually are discovered by the doctor on a routine physical examination of the neck. Occasionally, a patient may notice a nodule as a small lump in their neck when looking in the mirror. Once a nodule is discovered, a physician will carefully evaluate the nodule.

History. The doctor will need to take a detailed history, evaluating both past and present medical problems. If the patient is younger than 20 or older than 70 years of age, there is an increased likelihood that a nodule is cancerous. Similarly, if there is any history of radiation exposure (it was actually a standard treatment to apply radiation to the head and neck in the 1950’s to treat acne!), difficulty swallowing, or a change in the voice, the nodule is more likely to be cancerous. Although women tend to have more thyroid nodules than men, the nodules found in men are more likely to be cancerous. Despite its value, the history cannot differentiate benign from malignant nodules. Thus, many patients with risk factors uncovered in their history will have benign lesions, while others without risk factors for malignant nodules may still have thyroid cancer.

Physical examination. The physician should determine if there is one nodule or many nodules, and what the rest of the gland feels like. If the nodule is fixed to the surrounding tissue (it is not movable), the probability of cancer is higher. In addition, the physical exam should include a search for any abnormal lymph nodes in the nearby area that may suggest the spread of cancer.

Blood tests. Initially, blood tests should be done to assess the function of the thyroid. These tests include the thyroid hormones, T3 and T4, and the hormone that stimulates the thyroid gland to produce a thyroid hormone, called thyroid stimulating hormone (TSH). Elevated thyroid hormones and a low TSH suggest hyperthyroidism. Reduced thyroid hormones and a high TSH suggest hypothyroidism. If surgery is likely to be considered for treatment, it is strongly recommended that the physician also determine the blood level of thyroglobulin. Thyroglobulin is a protein for carrying thyroid hormones in the blood stream, and it is only produced in the thyroid gland. Thus, if a gland is completely removed, thyroglobulin levels fall. If thyroglobulin levels start to climb after surgery, there is concern that the cancer may have recurred, either close to the site where the thyroid was removed or elsewhere in the body.

Ultrasonography. While evaluating the thyroid gland, a physician may order an ultrasound examination of the thyroid. The ultrasound examination can:

  • Detect nodules that are not easily felt
  • Determine the number of nodules and their sizes
  • Determine if a nodule is solid or cystic
  • Be used to assist in obtaining tissue from the thyroid gland or nodule with a fine needle

Despite its value, an ultrasound cannot determine whether a nodule is benign or cancerous.

Radionuclide scanning. Radionuclide scanning with radioactive chemicals is another imaging technique a physician may use to evaluate a thyroid nodule. The normal thyroid gland accumulates iodine from the blood and uses it to make thyroid hormones. Thus, when radioactive iodine (I 123) is administered orally or intravenously to an individual, it accumulates in the thyroid and causes the gland to “light up” when imaged by a nuclear camera (a type of Geiger counter). The rate of accumulation gives an indication of how the thyroid gland and any nodules are functioning. A “hot spot” appears if a part of the gland or a nodule is producing too much hormone. Non-functioning or hypo-functioning nodules appear as “cold spots” on scanning. A cold nodule has a risk of cancer that is higher than a normally or hyper-functioning nodule. Cancerous nodules are more likely to be cold because cancer cells are abnormal and don’t accumulate the iodine as well as normal thyroid tissue.

Fine needle aspiration. A fine needle aspirate (FNA) of a nodule, a type of biopsy, is the most common direct way to determine what types of cells are present in the thyroid gland and in nodules. The needle is very small, and while the procedure is simple and can be done in a doctor’s office, anesthetic usually is injected into the tissues traversed by the needle. Fine needle aspiration is possible if the nodule is easily felt. If the nodule is more difficult to feel, fine needle aspiration can be performed under the guidance of ultrasound. The needle is inserted into the thyroid gland or the nodule and cells are withdrawn. Usually, several samples are taken in order to give the best chance of detecting abnormal cells. The cells are then examined by a pathologist under a microscope. The value of fine needle aspiration is dependent on the experience of the physician performing the procedure as well as the pathologist reading the specimen.

Diagnoses that can be made from fine needle aspiration include:

Benign thyroid tissue (non-cancerous), which can be consistent with Hashimoto’s thyroiditis or a colloid nodule or cyst. This result is obtained in about 60% of biopsies.

Cancerous tissue (malignant), consistent with the diagnosis of papillary, follicular, or medullary cancer. This result is obtained in about 5% of biopsies. The majority are papillary cancers.

Suspicious biopsy, showing a follicular adenoma. Though usually benign, up to 20% of these nodules are found ultimately to be cancerous.

Non-diagnostic, usually because not enough cells are obtained. If repeated, up to 50% of these cases will be able to be diagnosed as benign, cancerous, or suspicious.

One of the most difficult problems for a pathologist is to be confident that a follicular adenoma —usually a benign nodule—is not a follicular cell carcinoma or cancer. In these cases, it is up to the physician and the patient to weigh the option of surgery on a case-by-case basis, with less reliance on the pathologist’s interpretation of the biopsy. It is also important to remember that there is a small (3%) risk that a benign nodule diagnosed by fine needle aspiration may still be cancerous. Thus, even benign nodules should be followed closely by the patient and physician. Another biopsy may be necessary, especially if the nodule is growing. While most thyroid cancers are not very aggressive, that is, they do not spread rapidly, the exception is poorly differentiated (anaplastic) carcinoma, which spreads rapidly and is difficult to treat.

What is the treatment for thyroid nodules?
Because of the difficulty in distinguishing follicular adenomas from follicular cancers, patients with either of these two types of nodules, other nodules that are highly suspicious for cancer, and, of course, with definite cancer, should undergo surgery if they are healthy enough to withstand surgery. Most thyroid cancers are curable and rarely cause life-threatening problems. Any nodule not removed needs to be watched closely with an examination and follow-up with the physician every 6-12 months. This follow-up may involve a physical examination, ultrasound examination, or both. Occasionally, a physician may attempt to shrink the nodule by using suppressive doses of a thyroid hormone. Some physicians believe that if a nodule shrinks on suppressive therapy, it is more likely to be benign, and if the nodule continues to grow regardless of suppressive therapy, surgery should be strongly considered. The value of suppressive therapy, however, is controversial.

If a nodule is causing hyperthyroidism, it is usually benign. Treatment is aimed at preventing the signs and symptoms of hyperthyroidism such as heart failure, osteoporosis, and rapid heart rate. Treatments include destroying the gland using radioactive iodine (this time with the iodine isotope 131), blocking the production of thyroid hormones with medications, or just following a patient if the hyperthyroidism is mild.

Related Surgeons

Rana N. Ahmad, MD, FACS

Rana N Ahmad, MD, FACS attended the University of North Dakota, working with the Affiliated Hospital Program, Department of Surgery from 1991 to 1997 His practice includes an area of specialized interest in oncology, laparoscopic and gastrointestinal surgery Dr Ahmad is chairman of the surgery…