A thyroid nodule is defined as a small lump of tissue (either solid or cystic - filled with fluid), usually more than one quarter of an inch in diameter that may protrude from the neck's surface or may form in the thyroid gland itself. The nodule can be either benign (non-cancerous) or malignant (cancerous).
Even though the incidence of thyroid nodules (4 to 7 percent of the population) and thyroid cancer (1 percent of the population) is rare, there are certain risk factors that could make a person susceptible to thyroid cancer. The risk factors are:
- Age - Less than 20 years of age or over 60 years of age
- Exposure to ionizing radiation, especially in childhood
- A family history of thyroid cancer
Most people are asymptomatic (no symptoms) when thyroid nodules are first discovered. However, a noticeable lump or enlarged lymph nodes in neck may be an indication of a thyroid-related problem. More severe symptoms, such as thyroid pain, difficulty in swallowing, hoarseness or vocal cord paralysis and airway obstruction may be an indication of a possible malignant thyroid tumor.
The diagnosis a thyroid nodule is made by asking questions about risk factors and underlying health, a physical examination, a laboratory test called TSH, diagnostic imaging and fine-needle aspiration (FNA).
The physical examination includes checking the thyroid gland for possible enlargement (commonly called a goiter), its adjacent lymph nodes for any pain, tenderness and swelling, and the nodule itself for consistency, size and texture. If the nodule is soft, smooth and mobile, chances are the nodule is benign. If the nodule is firm, hard, irregular and fixed, the nodule may be malignant.
TSH (thyroid-stimulating hormone) blood test is administered to document thyroid function and to determine the presence of hyper- (overactivity of the thyroid gland) and hypo- (underactivity of the thyroid gland) thyroidism.
Diagnostic imaging may include ultrasonography of the thyroid gland as well as radionuclide scanning (called a thyroid scan). Ultrasonography or ultrasound is used to determine if the nodule is solid or cystic and how many nodules there are. It cannot determine if the nodule is benign or malignant, but it is a good indicator of whether a nodule is increasing or decreasing in size. The thyroid scan is used to provide information about the location, anatomy and the function of the thyroid gland.
For the thyroid scan, an injection or an oral dose of a radioisotope substance is given. The radioisotope substance usually contains a tiny dose of specially prepared technetium or radioiodine that is absorbed by the thyroid tissue. In this procedure there are two classifications of thyroid nodules - "hot" and "cold" - depending on the absorption of the radioiodine determines the classification.
A hot nodule is one that concentrates radioiodine equal to or more than the surrounding thyroid tissue. Occasionally, the rest of the thyroid is not even visible on the scan because the hot nodule is making so much thyroid hormone that the function of the rest of the thyroid gland is suppressed. Hot nodules are never malignant.
A nodule that concentrates iodine poorly or not at all is termed cold. Although all cancers are cold, most benign tumors and cysts are also cold. In fact, only about 10 percent of solitary cold nodules prove to be malignant, however, the presence of a cold nodule is always an indication for further evaluation.
Needle aspiration is the most effective method for distinguishing benign and malignant thyroid nodules. This procedure involves numbing the skin over the nodule and inserting a tiny needle into the nodule for 10 to 60 seconds to obtain thyroid tissue for microscopic examination.
Individuals who are found to have thyroid cancer, or in whom the tissue samples are not adequate to exclude cancer, need to have their nodules removed surgically. This procedure is called a thyroidectomy.
Patients with benign thyroid nodules should be monitored periodically or treated with levothyroxine to suppress the nodule growth.
Indeterminate nodules should be removed if there is clinical suspicion of malignancy. In suspect nodules, levothyroxine therapy with follow-up ultrasound assessment for size is appropriate. Nodules that do not shrink significantly within six months should be removed.