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Tests and diagnosis
By Mayo Clinic staffAlthough you sometimes may see or feel a thyroid nodule yourself — usually just below and to the right or left of your Adam's apple — most are discovered when your doctor checks your neck during a routine medical exam. You'll likely be asked to swallow while your doctor examines your thyroid because a nodule in the thyroid gland will usually move up and down during swallowing, whereas a nodule that forms in other parts of your neck won't.
Sometimes a thyroid nodule is detected when you have an imaging test such as an ultrasound, computerized tomography (CT) or magnetic resonance imaging (MRI) scan to evaluate another condition in your head or neck. Nodules detected this way are usually smaller than those found during a physical exam.
Additional tests
Once a nodule is discovered, your doctor will want to determine whether it's malignant or associated with thyroid dysfunction. For that reason, you're likely to have one or more of the following tests:
- Thyroid function tests. Your thyroid gland produces two main hormones, thyroxine and triiodothyronine. The rate at which these hormones are released is part of a carefully controlled system involving your thyroid gland, your pituitary gland and your hypothalamus — an area at the base of your brain that acts as a thermostat for this system. Tests that measure blood levels of thyroxine, triiodothyronine and thyroid-stimulating hormone, which is released by your pituitary gland, can indicate whether your thyroid is producing too much thyroxine (hyperthyroidism) or too little (hypothyroidism). These tests can't determine if a nodule is benign or malignant, however.
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Fine-needle aspiration (FNA) biopsy. This test — FNA biopsy — is the most sensitive for distinguishing between benign and malignant thyroid nodules. During the procedure, your doctor inserts a thin needle — much smaller than the needles used to draw blood — in the nodule and removes a sample of cells. The procedure, which is carried out in your doctor's office, takes about 20 minutes and has few risks. Your doctor is likely to take several samples from a single nodule. If you have more than one nodule, your doctor will usually take samples from these as well. Often, your doctor will use ultrasound to help guide the placement of the needle. The samples are then sent to a laboratory and analyzed under a microscope.
Most nodules diagnosed using FNA biopsy are benign. These nodules may grow, but they aren't cancerous and won't spread beyond the thyroid gland. A small percentage of biopsied nodules are cancerous. This diagnosis is based on the characteristics of individual cells and patterns in clusters of cells that are different from normal thyroid tissue. In some cases, a pathologist can determine specific types of cancer from an FNA biopsy sample.
Sometimes there may not be enough cells in a sample to accurately determine whether a nodule is benign or malignant. In that case, you're likely to have the test repeated. And in some FNA biopsies, the test results are considered suspicious or indeterminate, which means there's no definitive way to tell from the biopsy sample whether the nodule is cancerous. Repeat biopsies usually aren't helpful in suspicious cases, so the next step may be surgery to remove the nodule for a definitive diagnosis.
- Ultrasonography. This imaging technique uses high-frequency sound waves rather than radiation to produce images. It provides the best information about the shape and structure of nodules and may be used to distinguish cysts from solid nodules, to determine if multiple nodules are present and as a guide in performing an FNA biopsy.
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Thyroid scan. Sometimes you may have a thyroid scan to help evaluate thyroid nodules. During this test, an isotope of radioactive iodine is injected into the vein on the inside of your elbow. You then lie on a table while a special camera produces an image of your thyroid on a computer screen.
Nodules that produce excess thyroid hormone — called hot nodules — show up on the scan because they take up more of the isotope than normal thyroid tissue does. Cold nodules are nonfunctioning and appear as defects or holes in the scan. Hot nodules are almost always noncancerous, but about 5 percent of cold nodules are cancerous.
The disadvantage of a thyroid scan is that it can't distinguish between benign and malignant cold nodules. The length of a thyroid scan varies, depending on how long it takes the isotope to reach your thyroid gland. You may have some neck discomfort because your neck is stretched back during the scan, and you'll be exposed to a small amount of radiation.
- Thyroid nodules. American Thyroid Association. www.thyroid.org/patients/brochures/Nodules_brochure.pdf. Accessed Oct. 9, 2008.
- Ross DS. Diagnostic approach to and treatment of thyroid nodules. http://www.uptodate.com/online/content/topic.do?topicKey=thyroid/8983&selectedTitle=1~70&source=search_result. Accessed Oct. 9, 2008
- Ross DS. Overview of thyroid nodule formation. http://www.uptodate.com/online/content/topic.do?topicKey=thyroid/2323&selectedTitle=2~70&source=search_result. Accessed Oct. 9, 2008.
- Approach to the Patient With a Thyroid Nodule. The Merck Manual for Healthcare Professionals. http://www.merck.com/mmpe/sec12/ch152/ch152b.html?qt=thyroid%20nodules&alt=sh. Accessed Oct. 9, 2008.
- Ridgway EC. Medical treatment of benign thyroid nodules: Have we defined a benefit? Annals of Internal Medicine. 1998;128:403
- Lee GA et al. Disorders of the Thyroid Gland. In: Lalwani AK. Current Diagnosis & Treatment in Otolaryngology — Head & Neck Surgery. 2nd ed. New York, N.Y.: The McGraw-Hill Companies; 2008. http://www.accessmedicine.com/content.aspx?aID=2829111. Accessed Dec. 16, 2008.
- Clark OH. Thyroid & Parathyroid: Evaluation of Thyroid Nodules & Goiter. In: Doherty GM et al. Current Surgical Diagnosis & Treatment. 12th ed. Ann Arbor, Mich.: The McGraw-Hill Companies; 2006. http://www.accessmedicine.com/content.aspx?aID=2061372. Accessed Dec. 16, 2008.
