Thyroid nodules are solid or fluid-filled lumps that form within your thyroid, a small gland located at the base of your neck, just above your breastbone.
Most thyroid nodules aren't serious and don't cause symptoms. Only a small percentage of thyroid nodules are cancerous.
You often won't know you have a thyroid nodule until your doctor discovers it during a routine medical exam. Or your doctor may uncover it during a scan that was done for another health reason. Some thyroid nodules, however, may become large enough to be visible or make it difficult to swallow or breathe.
Treatment options depend on the type of thyroid nodule you have.
Symptoms
Most thyroid nodules don't cause signs or symptoms. But occasionally some nodules become so large that they can:
- Be felt
- Be seen, often as a swelling at the base of your neck
- Press on your windpipe or esophagus, causing shortness of breath or difficulty swallowing
In some cases, thyroid nodules produce additional thyroxine, a hormone secreted by your thyroid gland. The extra thyroxine can cause symptoms of an overproduction of thyroid hormones (hyperthyroidism), such as:
- Unexplained weight loss
- Increased sweating
- Tremor
- Nervousness
- Rapid or irregular heartbeat
Only a small number of thyroid nodules are cancerous. But determining which nodules are cancerous can't be done by evaluating your symptoms alone. Most cancerous thyroid nodules are slow growing and may be small when your doctor discovers them. Aggressive thyroid cancers are rare with nodules that may be large, firm, fixed and rapid growing.
Causes
Several conditions can cause nodules to develop in your thyroid gland, including:
- Overgrowth of normal thyroid tissue. An overgrowth of normal thyroid tissue is sometimes referred to as a thyroid adenoma. It's unclear why this occurs, but it's not cancerous and isn't considered serious unless it causes bothersome symptoms from its size.
Some thyroid adenomas lead to hyperthyroidism.
- Thyroid cyst. Fluid-filled cavities (cysts) in the thyroid most commonly result from degenerating thyroid adenomas. Often, solid components are mixed with fluid in thyroid cysts. Cysts are usually noncancerous, but they occasionally contain cancerous solid components.
- Chronic inflammation of the thyroid. Hashimoto's disease, a thyroid disorder, can cause thyroid inflammation and result in enlarged nodules. This often is associated with hypothyroidism.
- Multinodular goiter. The term goiter is used to describe any enlargement of the thyroid gland, which can be caused by iodine deficiency or a thyroid disorder. A multinodular goiter contains multiple distinct nodules within the goiter, but its cause is less clear.
- Thyroid cancer. The chances that a nodule is cancerous are small. However, a nodule that is large and hard or causes pain or discomfort is more worrisome. You will likely want to have it checked by your doctor.
Certain factors increase your risk of thyroid cancer, such as a family history of thyroid or other endocrine cancers and having a history of radiation exposure from medical therapy or from nuclear fallout.
- Iodine deficiency. Lack of iodine in your diet can sometimes cause your thyroid gland to develop thyroid nodules. But iodine deficiency is uncommon in the United States, where iodine is routinely added to table salt and other foods.
Diagnosis
In assessing a lump or nodule in your neck, one of your doctor's main goals is to rule out the possibility of cancer. But your doctor will also want to know if your thyroid is functioning properly. Tests include:
- Physical exam. Your doctor will likely ask you to swallow while he or she examines your thyroid because a nodule in your thyroid gland will usually move up and down during swallowing.
- Your doctor will also look for signs and symptoms of hyperthyroidism, such as tremor, overly active reflexes, and a rapid or irregular heartbeat. He or she will also check for signs and symptoms of hypothyroidism, such as a slow heartbeat, dry skin and facial swelling.
- Thyroid function tests. Tests that measure blood levels of thyroid-stimulating hormone (TSH) and hormones produced by your thyroid gland can indicate whether you have hyperthyroidism or hypothyroidism.
- Ultrasound. This imaging technique uses high-frequency sound waves to produce images of your thyroid gland. A thyroid ultrasound provides the best information about the shape and structure of nodules. Doctors may use it to distinguish cysts from solid nodules or to determine if multiple nodules are present. Doctors may also use it as a guide in performing a fine-needle aspiration biopsy.
- Fine-needle aspiration biopsy. Nodules are often biopsied to make sure no cancer is present. During the procedure, your doctor inserts a very thin needle in the nodule and removes a sample of cells.
The procedure is usually done in your doctor's office, takes about 20 minutes and has few risks. Often, your doctor will use ultrasound to help guide the placement of the needle. Your doctor then sends the samples to a laboratory to have them analyzed under a microscope.
- Thyroid scan. Your doctor may recommend a thyroid scan to help evaluate thyroid nodules. During this test, an isotope of radioactive iodine is injected into a vein in your arm. 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. Hot nodules are almost always noncancerous.
In some cases, nodules that take up less of the isotope — called cold nodules — are cancerous. However, a thyroid scan can't distinguish between cold nodules that are cancerous and those that aren't cancerous.
