This page is written assuming you have read the introductory page on thyroid nodules first. If you have not, please do so because it will make this page easier to understand.

Thyroid nodules increase with age and are present in almost ten percent of the adult population. Autopsy studies reveal the presence of thyroid nodules in 50 percent of the population, so they are fairly common. Ninety-five percent of solitary thyroid nodules are benign, and therefore, only five percent of thyroid nodules are malignant. Common types of the benign thyroid nodules are adenomas (overgrowths of "normal" thyroid tissue), thyroid cysts, and Hashimoto's thyroiditis. Uncommon types of benign thyroid nodules are due to subacute thyroiditis, painless thyroiditis, unilateral lobe agenesis, or Riedel's struma. As noted on previous pages, those few nodules which are cancerous are usually due to the most common types of thyroid cancers which are the differentiated" thyroid cancers. Papillary carcinoma accounts for 60 percent, follicular carcinoma accounts for 12 percent, and the follicular variant of papillary carcinoma accounting for six percent. These well differentiated thyroid cancers are usually curable, but they must be found first. Fine needle biopsy is a safe, effective, and easy way to determine if a nodule is cancerous.


Thyroid cancers typically present as a dominant solitary thyroid nodule which can be felt by the patient or even seen as a lump in the neck by his/her family and friends. This is illustrated in the picture above. As pointed out on our page introducing thyroid nodules, we must differentiate benign nodules from cancerous solitary thyroid nodules. While history, examination by a physician, laboratory tests, ultrasound, and thyroid scans (shown in the picture below) can all provide information regarding a solitary thyroid nodule, the only test which can differentiate benign from cancerous thyroid nodules is a biopsy (the term biopsy means to obtain a sample of the tissue and examine it under the microscope to see if the cells have taken on the characteristics of cancer cells). Thyroid cancer is no different in this situation from all other tissues of the body...the only way to see if something is cancerous is to biopsy it. However, thyroid tissues are easily accessible to needles, so rather than operating to remove a chunk of tissue with a knife, we can stick a very small needle into it and remove cells for microscopic examination. This method of biopsy is called a fine needle aspiration biopsy, or "FNA".


What is a cold nodule? Thyroid cells absorb iodine so they can make thyroid hormone out of it. When radioactive iodine is given, a butterfly image will be obtained on x-ray film showing the outline of the thyroid. If a nodule is composed of cells which do not make thyroid hormone (don't absorb iodine) then it will appear "cold" on the x-ray film. A nodule which is producing too much hormone will show up darker and is called "hot". [A hot nodule is shown on our page describing the causes of hyperthyroidism].


The evaluation of a solitary thyroid nodule should always include history and examination by a physician. Certain aspects of the history and physical exam will suggest a benign or malignant condition. Remember, a biopsy of some sort is the only way to tell for sure.

family history of Hashimoto's thyroiditis
family history of benign thyroid nodule or goiter
symptoms of hyperthyroidism or hypothyroidism
pain or tenderness associated with a nodule
a soft, smooth, mobile nodule
multinodular goiter without a predominant nodule (lots of nodules, not one main nodule)
"warm" nodule on thyroid scan (produces normal amount of hormone)
simple cyst on ultrasound

age less than 20
age greater than 70
male gender
new onset of swallowing difficulties
new onset of hoarseness
history of external neck irradiation during childhood
firm, irregular and fixed nodule
presence of cervical lymphadenopathy (swollen hard lymph nodes in the neck)
previous history of thyroid cancer
nodule that is "cold" on scan (shown in picture above, meaning the nodule does not make hormone)
solid or complex on ultrasound

Thyroid hormone levels are usually normal in the presence of a nodule, and normal thyroid hormone levels do not differentiate benign from cancerous nodules. However, the presence of hyperthyroidism or hypothyroidism favors a benign nodule (thats why a "warm" nodule or a "hot" nodule favors a benign condition). Thyroglobulin levels are useful tumor markers once the diagnosis of malignancy has been made, but are nonspecific in regard to differentiating a benign from a cancerous thyroid nodule. Ultrasound accurately determines thyroid gland volume, number and size of nodules; separates thyroid from nonthyroidal masses; helps guide fine needle biopsy when necessary; and can identify solid nodules as small as 3 mm and cystic nodules as small as 2 mm. Although several ultrasound features favor the presence of a benign nodule, and other ultrasound features favor the presence of a cancerous nodule. Ultrasound alone cannot be used to differentiate benign from malignant nodules. This is covered more completely on our nodule/ultrasound page. And since 15 percent of cystic thyroid nodules are malignant, ultrasound determination that a nodule is cystic does not rule out thyroid cancer.

Nodules detected by thyroid scans are classified as cold, hot or warm. Eighty-five percent of thyroid nodules are cold, 10 percent are warm, and five percent are hot. An excellent example of a cold scan is shown above, but remember that 85 percent of cold nodules are benign, 90 percent of warm nodules are benign, and 95 percent of hot nodules are benign. [got all that???] Although thyroid scanning can give a probability that a nodule is benign or malignant, it cannot truly differentiate benign or malignant nodules and usually should not be used as the only basis for recommending treatment of the nodule, including thyroid surgery.

Thyroid fine needle aspiration (FNA) biopsy is the only non-surgical method which can differentiate malignant and benign nodules in most, but not all, cases. The needle is placed into the nodule several times and cells are aspirated into a syringe. The cells are placed on a microscope slide, stained, and examined by a pathologist. The nodule is then classified as nondiagnostic, benign, suspicious or malignant.

• Nondiagnostic indicates that there are an insufficient number of thyroid cells in the aspirate and no diagnosis is possible. A nondiagnostic aspirate should be repeated, as a diagnostic aspirate will be obtained approximately 50 percent of the time when the aspirate is repeated. Overall, five to 10 percent of biopsies are nondiagnostic, and the patient should then undergo either an ultrasound or a thyroid scan for further evaluation.
  
  
• Benign thyroid aspirations are the most common (as we would suspect since most nodules are benign) and consist of benign follicular epithelium with a variable amount of thyroid hormone protein (colloid).
  
  
• Malignant thyroid aspirations can diagnose the following thyroid cancer types: papillary, follicular variant of papillary, medullary, anaplastic, thyroid lymphoma, and metastases to the thyroid. Follicular carcinoma and Hurthle cell carcinoma cannot be diagnosed by FNA biopsy. This is an important point. Since benign follicular adenomas cannot be differentiated from follicular cancer (~12% of all thyroid cancers) these patients often end up needing a formal surgical biopsy, which usually entails removal of the thyroid lobe which harbors the nodule.
  
  
• Suspicious cytologies make up approximately 10 percent of FNA's. The thyroid cells on these aspirates are neither clearly benign nor malignant. Twenty five percent of suspicious lesions are found to be malignant when these patients undergo thyroid surgery. These are usually follicular or Hurthle cell cancers. Therefore, surgery is recommended for the treatment of thyroid nodules from which a suspicious aspiration has been obtained.

FNA is the first, and in the vast majority of cases, the only test required for the evaluation of a solitary thyroid nodule.

Several studies reveal that suppression with thyroid hormone does not decrease the size of thyroid nodules. Therefore, unless a nodule is growing or becoming symptomatic, it is not necessary to suppress the nodule. In addition, suppression of a thyroid nodule would require long-term TSH suppression, potentially increasing the risk of osteoporosis in these patients. While there has been a traditional distinction between thyroid glands with a solitary nodule and multinodular goiters, it has been shown that approximately 50 percent of patients with a solitary nodule on exam will have additional nodules on thyroid ultrasound. Therefore, the differentiation between solitary nodules and multinodular goiters is becoming less clear-cut. It has also been believed for many years that the presence of a multinodular goiter reduces the likelihood that a thyroid cancer is present, yet recent studies indicate that there might be an equal likelihood for developing thyroid cancer in a multinodular goiter just as in a solitary thyroid nodule. If a multinodular goiter has a predominant nodule, the predominant nodule should be biopsied.

In conclusion, FNA of the thyroid is a safe, inexpensive and effective way to distinguish a benign from a malignant nodule and usually should be the first diagnostic test performed.

More about Thyroid Ultrasound

More about Thyroid Cancer

Back to the basics about Thyroid Nodules

Much of this information was obtained from an article published in the journal Endocrinologist (November, 1996) which was written by Mark Stesin, M.D. His expertise is acknowledged. This page was written by James Norman, M.D.