Thyroid Nodules (cont.)
Ruchi Mathur, MD, FRCP(C)
Ruchi Mathur, MD, FRCP(C)
Ruchi Mathur, MD, FRCP(C) is an Attending Physician with the Division of Endocrinology, Diabetes and Metabolism and Associate Director of Clinical Research, Recruitment and Phenotyping with the Center for Androgen Related Disorders, Department of Obstetrics and Gynecology at Cedars-Sinai Medical Center.
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How are thyroid nodules diagnosed?
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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 the 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. In addition to evaluating the area of the thyroid, the physician should look for any signs of gland malfunction, such as an overproduction or underproduction of thyroid hormone (hyperthyroidism and hypothyroidism).
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 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. A blood test called antithyroid peroxidase antibodies is useful in diagnosing autoimmune thyroiditis, for example, Hashimoto's thyroiditis. 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:
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:
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.
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