What Is a Thyroid Colloid Cyst?

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A thyroid colloid cyst (TCC) is a common, noncancerous nodule in the thyroid gland that is filled with colloid, a stored form of thyroid hormone.

Many thyroid colloid cysts do not require treatment, but follow-up exams can monitor for any growth or changes. In some cases, surgical removal may be recommended.

This articles reviews the symptoms and causes of thyroid colloid cysts, as well as how they are diagnosed and treated.

Doctor feeling female patient's thyroid gland

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Thyroid Colloid Cysts and Other Nodules

Thyroid colloid cysts are just one type of thyroid nodule—a small tumor the forms inside the thyroid gland. Thyroid nodules are very common. About 60% of adults have at least one. Fortunately, about 95% of these are noncancerous.

A thyroid nodule is not always filled with fluid. But when it is, as is the case with thyroid colloid cysts, it is considered cystic.

Colloid nodules may be completely fluid-filled or partially-fluid filled with some solid areas. Purely cystic nodules (meaning 100% fluid-filled) are rarely cancerous.

Though a colloid thyroid nodule may increase in size, it remains in the thyroid and does not spread to other areas of the body.

It's possible to develop other thyroid nodules, such as hyperplastic nodules and follicular adenomas. A goiter describes an enlarged thyroid that either encompasses the entire gland or appears as bumpy nodules.

Some patients have more than one type of nodule at the same time.

What Is the Thyroid?

The thyroid is a gland located at the base of the neck, below the Adam’s apple or larynx. It has a right and left lobe, connected by the isthmus, which is like a bridge. The thyroid secretes thyroid hormones. These hormones affect various body systems, influencing heart function, metabolism, temperature regulation, and more.

Symptoms of a Colloid Cyst on the Thyroid

Most thyroid colloid cysts do not produce any signs or symptoms unless they become large enough to affect surrounding tissues or are noticeable on the neck.

When thyroid colloid cysts have symptoms, they may include:

  • A visible swelling in the neck or bump that can be felt
  • Hoarseness or voice changes
  • Pain in the neck
  • Problems swallowing

In some cases, thyroid nodules may produce hormones and cause symptoms of overactive thyroid (hyperthyroidism), including:

  • Sudden, rapid weight loss
  • Fast or irregular pulse
  • Nervousness or anxiety

It's also possible to have symptoms of an underactive thyroid (hypothyroidism), such as:

  • Fatigue
  • Dry Skin
  • Weight gain
  • Constipation

Causes of Thyroid Colloid Cysts

Thyroid nodules are usually caused by an overgrowth of normal thyroid tissue, but it's unknown why this happens. A breakdown of excess tissue may also contribute to a cyst, and thyroid cysts can include a mixture of fluid and solid material.

Risk factors for developing thyroid nodules include smoking or living in areas with iodine deficiency (uncommon the U.S.). They become more common as you age.

Cancer Risk

For every 20 thyroid nodules that can be felt on physical examination, one is cancerous. Examples of cancerous thyroid nodules include papillary or follicular carcinomas, medullary cancer, or anaplastic cancer.

Exposure to ionizing radiation (from cancer treatments, occupational exposure, or nuclear fallout) increases thyroid cancer risk, especially if the exposure happened during childhood. Nodules that grow rapidly or cause a hoarse-sounding voice tend to be more concerning.

You may suspect that a painful thyroid nodule is cancerous. However, that's not necessarily the case. Chronic inflammation of the thyroid gland can produce inflammatory nodules or a swollen thyroid gland.

Like many cancers, thyroid cancer can run in families. Your healthcare provider will take your family history and lifestyle factors into account when assessing your risk of thyroid cancer.

Nonfunctioning nodules (meaning they don't produce thyroid hormone) have a 14% to 22% risk of being cancerous compared to hyperfunctioning nodules (nodules that produce thyroid hormone), which are rarely cancerous.

Although hyperfunctioning thyroid nodules don't tend to cause cancer, they can result in other unpleasant side effects. By overproducing thyroid hormones, hyperfunctioning thyroid nodules can lead to symptoms of hyperthyroidism (including osteoporosis and abnormal heartbeats).

Ongoing monitoring and treatment can help keep hyperfunctioning thyroid nodules under control.

Can Colloid Thyroid Cysts Turn Cancerous?

Thyroid cysts rarely develop into cancer, but they can. Monitoring is required to determine whether a nodule is growing and may be turning cancerous. If you have multiple nodules, each one should be evaluated individually. If there's growth or you have certain risk factors, additional testing for cancer may be needed.


Nodules are more common in women and the incidence increases with age. Depending on the size and location of a nodule, it may be palpable (able to be felt) during a physical exam. About 5% of women and 1% of men living in iodine-sufficient areas have palpable nodules.

Nonpalpable nodules are usually discovered through imaging studies such as an ultrasound, computed tomography (CT) scan, or magnetic resonance imaging (MRI) of the neck or surrounding areas. High-resolution ultrasounds are particularly effective and detect thyroid nodules in up to 68% of healthy individuals.

If your healthcare provider finds a thyroid nodule, the next step is ordering a blood test to measure your levels of thyroid-stimulating hormone (TSH) and assess your thyroid function. Performing an ultrasound will help evaluate the type of nodule and check the surrounding lymph nodes in the neck.

Based on the results of these tests and other risk factors, further testing may be required. It can be helpful to undergo the following tests.

Radioactive Iodine Uptake Test

This test is reserved for patients who have a thyroid nodule and have lower than normal TSH. A radionuclide (radioactive iodine) is taken by mouth, in the form of a pill.

Imaging studies are performed six hours later, or even the next day. Waiting provides enough time to allow the radioactive iodine to reach the thyroid. The results of this test can determine if the nodule is hyperfunctioning (unlikely to be cancerous) or nonfunctioning.

Fine-Needle Aspiration (FNA)

For nonfunctioning nodules, fine-needle aspiration may be required (depending on the ultrasound findings and the size of the nodule). During this procedure, the practitioner inserts a thin needle through the skin and into the thyroid nodule to collect cells for testing.

Performing FNA while using an ultrasound machine helps ensure the correct placement of the needle. You may receive medication to numb the area of the neck to prevent discomfort. Your healthcare provider will take multiple cell samples from different areas of the nodule to analyze for cancerous characteristics.

Molecular Testing

Sometimes the results of the FNA come back as “indeterminate” meaning the results are inconclusive as to whether the cells are cancerous or benign. Your healthcare provider may send the sample for molecular testing. Molecular testing analyzes the genetic sequence of the cells' DNA or RNA to check for mutations.

Thyroid Colloid Cyst Monitoring and Treatment

Many thyroid nodules remain stable in size. Some may shrink spontaneously or even disappear entirely without any treatment. Still, monitoring is important.

Benign thyroid nodules are monitored with a follow-up ultrasound one to two months after the initial discovery. If there has been no significant growth, repeat ultrasounds are typically performed every three to five years.

If your healthcare provider is concerned about a nodule's growth rate, you may need another ultrasound or FNA testing to rule out cancer. These test results will help guide treatment and follow-up recommendations.

Surgical Removal

Cysts are usually noncancerous, but they occasionally contain cancerous solid components. Even benign cysts may require removal if they have significant growth.

Removal may be recommended in cases of:

  • Thyroid cancer or genetic tests that indicate cancer is likely
  • A nodule large enough to cause pain and/or affect your breathing, speech, or ability to swallow
  • A nodule that affects your production of thyroid hormones

Treatment options include:

  • Thyroid radiofrequency ablation: A minimally invasive option that involves using an ultrasound-guided needle to transfer an electrical current to the nodule, heating it up and shrinking it. This type of procedure is typically recommended for large, benign nodules.
  • Thyroid lobectomy: Surgical removal of one of the two lobes of the thyroid gland. It may be done for thyroid nodules or cancers.
  • Thyroidectomy: Surgical removal of the entire thyroid gland or almost all of it. This may be recommended for certain cancers or goiters.

Surgical removal usually requires general anesthesia, which puts you into a sleep-like state for the surgery. The surgeon usually makes the incision along the crease of the neck to avoid a scar and cuts out part or all of the thyroid.

If it's thyroid cancer, surgery is typically done and there may be additional thyroid cancer treatments recommended, such as chemotherapy or radiation.

A Word From Verywell

Noticing a thyroid nodule on your neck or having one discovered during a routine examination can be alarming. There are several tests available to help your practitioner determine whether the nodule is concerning or harmless.

Most of the time, the only recommended treatment is ongoing monitoring to keep an eye out for any changes. Let your healthcare provider know if you suspect a growth on your thyroid so they can rule out potential dangers and you can learn more about the best next steps to take.

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Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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By Anastasia Climan, RDN, CD-N
Anastasia, RDN, CD-N, is a writer and award-winning healthy lifestyle coach who specializes in transforming complex medical concepts into accessible health content.