Thyroid nodules are collections of abnormal cells that form lumps in the thyroid gland. Between 90 and 95 percent of these nodules are noncancerous (benign). However, in uncommon cases, nodules are cancerous (malignant). For this reason, patients are urged to have nodules checked by a physician.

Thyroid nodules are the most common endocrine condition in the United States, according to the American Thyroid Association. Patients may have one nodule or several. In most cases, experts do not know why they form. However, risk factors include age and certain thyroid diseases.

In many cases, patients with thyroid nodules do not experience any symptoms and are unaware of their condition. However, some patients may discover a lump in the front of their neck that appears to grow larger over time. Large nodules may impair breathing or swallowing.

Thyroid nodules are often discovered by a physician during a routine physical examination or during an imaging test ordered for another condition. A fine-needle aspiration biopsy, which is an analysis of thyroid cells removed with a thin needle, can usually determine whether or not a nodule is cancerous.

Because the vast majority of nodules are benign, physicians usually prefer to monitor rather than have them surgically removed. In some cases, medications may be used to reduce the size of thyroid nodules or prevent the growth of new nodules. When cancer is present, experts generally recommend surgical removal of cancerous nodules and the thyroid gland.

Thyroid nodules are lumps that can form in the thyroid gland. They are the most common endocrine condition in the United States, according to the American Thyroid Association. However, estimates of their incidence vary widely. The American Cancer Society reports that at least half of the general population develop them and usually do not even notice them, whereas the American Association of Clinical Endocrinologists states that 6 percent of women and 1 to 2 percent of men are diagnosed with thyroid nodules.

Lumps in the thyroid glands occur due to an abnormal growth of thyroid cells. Patients may have just one thyroid nodule or a collection of several nodules.

Between 90 and 95 percent of these nodules are noncancerous (benign). Such nodules may not cause symptoms and usually do not pose significant health dangers. In some cases, the nodule may produce thyroid hormones, leading to excessive levels of hormones in the bloodstream (hyperthyroidism). Nodules that produce thyroid hormones are called autonomous nodules.

Different types of noncancerous nodules include:

• Colloid nodules. These nodules result from an overgrowth of normal tissue or storage of thyroid hormones.
  
  
• Hyperplastic nodules. Marked by excessive cellular activity and include several congenital (present at birth) types. These nodules may sometimes produce thyroid hormones.
  
  
• Adenomas. Benign nodules that include follicular and and Hurthle cell types. Adenomas sometimes produce thyroid hormones.
  
  
• Thyroid cysts. Nodules filled with blood or other fluid. Some cysts contain solid components (complex cysts). These are more likely to be cancerous than fluid-filled cysts.
  
  
• Inflammatory nodules. Nodules that develop as a result of inflammation of the thyroid gland (thyroiditis), particularly Hashimoto’s thyroiditis.

If a number of nodules are present, they can cause an enlargement of the thyroid gland (goiter). Enlargement due to the presence of several nodules is known as a multinodular goiter.

In uncommon cases, thyroid nodules may be cancerous (malignant). For this reason, patients are urged to have nodules checked by a physician. Cancer of the thyroid is usually highly treatable, especially if it is caught early.

Experts do not know why most thyroid nodules form. However, several factors are associated with the development of noncancerous thyroid nodules. They include:

• Overgrowth of normal thyroid gland tissue (goiter)
  
  
• Development of fluid-filled cysts
  
  
• Inflammation of the thyroid (thyroiditis), especially Hashimoto’s thyroiditis
  
  
• Benign or cancerous tumor
  
  
• Hypothyroidism
  
  
• Genetic defect (associated with some autonomous nodules)
  
  
• Lack of dietary iodine (rare in the United States)

The risk of developing thyroid nodules increases with age. Thyroid nodules also tend appear more often in women than in men.

Risk factors associated with developing cancerous nodules include:

• Certain genetic conditions (mutation in a gene called RET proto-oncogene, or hereditary disorders including Gardner’s syndrome, familial polyposis or Cowden’s disease)
  
  
• Family history of medullary thyroid carcinoma or multiple endocrine neoplasia type II
  
  
• History of radiation exposure to the head or neck
  
  
• Male gender
  
  
• Age (younger than 20 or older than 70)

In many cases, patients with thyroid nodules do not experience any symptoms and are unaware of their condition. However, some patients may discover a lump in the front portion of their neck that appears to grow larger over time. Large nodules that press against the esophagus (tube that carries food from the throat to the stomach) or trachea (windpipe) may cause discomfort or pressure when swallowing. They may also cause breathing difficulties. Large nodules also can cause pain in the ear, jaw or neck. In rare cases, the nodule may irritate a nerve in the voice box, leading to hoarseness.

Nodules that are cancerous are more likely than noncancerous nodules to cause hoarseness, breathing difficulties (dyspnea) and swallowing problems (dysphagia). Cancerous nodules also tend to grow more quickly, become harder and may cause the lymph nodes under the jaw or in the neck to become enlarged.

Difficulty breathing or swallowing may also be symptoms of other conditions, including multinodular goiter (a type of goiter) or Riedel’s thyroiditis (a rare form of thyroiditis). Thyroid nodules also may be associated with hyperthyroidism or hypothyroidism.

Thyroid nodules often are discovered by a physician during a routine physical examination. The physician may feel a lump in the neck or discover that the thyroid gland is enlarged. In other cases, nodules may be discovered when a patient is undergoing an imaging test (e.g., x-ray, ultrasound, CAT scan, MRI) related to another condition, such as spinal arthritis or carotid artery disease.

When a nodule is discovered, the physician is likely to order blood tests to determine whether the thyroid is functioning properly and if thyroiditis is present. However, most patients with thyroid nodules will have normal results from thyroid blood tests.

A physician may also take steps to determine whether a nodule is cancerous. A fine-needle aspiration biopsy is the primary test used to determine whether or not a nodule is cancerous. A very thin needle is inserted into the nodule to remove cells that are analyzed under a microscope for signs of cancer. A local anesthetic may be applied, and discomfort is minimal. Several tissue samples are typically obtained during the procedure, which takes about 20 minutes and usually is performed in a physician’s office.

In 75 percent of cases, a fine-needle aspiration biopsy provides enough information to formulate an accurate treatment plan, according to the American Association of Clinical Endocrinologists.

Between 60 and 80 percent of test results indicate that a nodule is benign, according to the American Cancer Society. About 10 percent of results indicate a suspicious nodule, which usually turns out to be either a noncancerous follicular adenoma or follicular cancer. Such suspicious nodules may require a thyroid scan before a more definitive diagnosis can be made.

In about 5 percent of cases, a nodule can be clearly identified as cancerous. Such nodules are often a form of papillary cancer.

In up to 20 percent of cases, a fine-needle aspiration biopsy fails to provide enough information to make a conclusive diagnosis. This is most likely when patients have fluid-filled nodules or nodules consisting of a follicular cell type. Repeat testing may reveal more clues as to the nature of the nodule. A surgical biopsy may also be performed. In other cases, physicians rely on other clues and their own expertise to make a judgment as to whether or not the nodule requires treatment.

Imaging tests that may be used to help diagnose whether or not a thyroid nodule is cancerous include:

• Thyroid scan. A test in which the patient is given a small dose of a radioactive isotope before the thyroid is scanned with a special camera. The image that is created reveals whether the thyroid nodule is functioning normally or if it shows signs of being cancerous. However, the thyroid scan is often inconclusive regarding whether or not a nodule is cancerous. For this reason, the technique is infrequently used for this type of diagnosis. Instead, the thyroid scan is used to provide additional information after a fine-needle aspiration biopsy indicates that a nodule is suspicious.
  
  
• Thyroid ultrasound. Procedure in which images are generated by bouncing high-frequency sound waves off the thyroid. Ultrasound can reveal the presence of thyroid nodules that are as small as 2 to 3 millimeters. However, as with a thyroid scan, ultrasound rarely provides enough information to confirm whether or not a nodule is cancerous. More often, ultrasound is used to help guide a needle into the nodule during a fine-needle biopsy. A thyroid ultrasound may also be used to monitor the potential growth of a nodule after a fine needle aspiration biopsy has determined that the nodule is benign.

There is no known method to prevent thyroid nodules. Until recently, thyroid surgery was used to remove most thyroid nodules. However, this approach is used less frequently today, as experts now recognize that the vast majority of thyroid nodules are noncancerous (benign). Today, physicians usually prefer to monitor the development of benign thyroid nodules. Nodules that remain stable or decrease in size usually do not require surgical removal.

Radioactive iodine may be prescribed to reduce the size of autonomous nodules and relieve hyperthyroidism, although this procedure should not be used in pregnant women.

In some cases, thyroid hormone medication may be used in an effort to reduce the size of thyroid nodules or prevent the growth of additional nodules. However, this treatment does not appear to help most patients with thyroid nodules, according to the National Institutes of Health, and potential side effects include heart problems and reduced bone density.

Surgical removal of a nodule may be suggested if it is unknown whether the nodule is cancerous, or if it continues to grow and interferes with activities such as breathing, swallowing or speaking.

If a nodule is found to cancerous, the entire thyroid gland and any abnormal lymph nodes should be surgically removed, according to the American Academy of Endocrinologists. Thyroid cancer is one of the least deadly cancers and has a high survival rate, according to the American Cancer Society. Removal of the thyroid (total thyroidectomy) results in hypothyroidism, which requires thyroid hormone medication for the rest of the patient’s life.

Researchers are exploring use of focused, high-intensity ultrasound as a potential alternative to surgical removal of cancerous thyroid nodules.

Preparing questions in advance can help patients have more meaningful discussions with their physician regarding their conditions. Patients may wish to ask their doctor the following questions about thyroid nodules:

1. What makes you suspect I may have a thyroid nodule?
   
   
2. What sort of tests will you perform to confirm your diagnosis? Do I need to do anything to prepare for these tests?
   
   
3. How will you determine if my thyroid nodule is cancerous? How soon will I know the results?
   
   
4. What type of thyroid nodule do I have? Is the nodule a sign that my thyroid is producing too much or too little thyroid hormone?
   
   
5. Will my thyroid nodule require treatment, or can it simply be monitored?
   
   
6. If I require treatment, what are my options?
   
   
7. What are the risks and benefits of these treatments?
   
   
8. How often will I need to be monitored so that you can track the progress of my condition?
   
   
9. If my nodule is cancerous, do you recommend removing my thyroid gland in addition to the nodule? If so, how will this affect me?
   
   
10. What is my long-term prognosis?
    
    
11. Am I likely to develop more thyroid nodules in the future? What are the chances they will be cancerous?