The thyroid is located at the base of the neck. It is a small, butterfly-shaped gland that produces thyroid hormones such as thyroxine or T4 and triiodothyronine or T3. These hormones are required for the regulation of the metabolism as they tell your cells how fast to use energy and produce protein. This gland is also responsible to produce calcitonin, which is the hormone that regulates calcium levels in the blood by preventing the breakdown of bone. It also increases the elimination of calcium from the kidneys. To control the amounts of T3 and T4, the body has an elaborate feedback system.
When there is a decrease in the hormones in the blood, the hypothalamus will release thyrotropin-releasing hormones. These tell the pituitary gland to start releasing the thyroid-stimulating hormone TSH. The thyroid gland will then start to produce and release T4 and T3.
As the thyroid hormone levels begin to increase, the pituitary gland will reduce the amount of TSH released. This will tell the thyroid to start producing less T4 and T3. In normal circumstances, this system will regulate the activity of the thyroid gland and ensure stable levels of necessary hormones in the blood.
The thyroid can suffer from thyroid nodules, which are abnormal growths in the tissue of the gland that causes a lump or swelling. These nodules can occur at any age but will be more common as people get older. They are also more common in women. According to the American Thyroid Association, approximately half of all people will have thyroid nodules that are visible on imaging by the age of 60. However, these nodules will only be large enough to detect in a physical exam in around 5% of adults.
Most thyroid nodules are found in people by chance because they do not cause any symptoms. They are usually found when imaging scans are done for other conditions such as routine neck evaluations. It is possible that you might notice a lump in your neck, and this should be brought to your doctor’s attention. When found, the nodules and the gland will need to be evaluated, but more than 90% are considered benign. However, a small percentage can be cancerous.
Thyroid nodules can:
- Exist as a single nodule or be present as multiple nodules
- Be filled with fluid, be solid or a mixture of both
- Be large or small
- Grow slowly, but some can grow rapidly while others shrink
- Occasionally be large enough to compress the throat causing difficulty breathing and swallowing as well as pain
- Rarely affects the vocal cords to cause hoarseness, and those that do are more likely to be cancerous
- Produce T3 or T4, but most will not.
Testing for Thyroid Nodules
The Initial Testing
To test for thyroid nodules, a combination of imaging tests and laboratory testing can be used. These tests will also evaluate the nodules and thyroid gland.
These tests will look for TSH but can look for T4free and T3free or Total T3. The test helps to determine if the gland is functioning correctly. These tests can also help to determine if the thyroid nodules are producing an excess of thyroid hormones.
One of the first tests generally ordered is an ultrasound of the thyroid gland. This scan will help with the evaluation of the thyroid nodules. The results of the test can help determine the location, shape, size, and other characteristics of the nodules. The test can also determine if there is more than one nodule. Ultrasounds can also:
- Evaluate the other structures in the neck such as the lymph nodes
- Determine if a fine needle aspiration biopsy will have to be done. If so, the test can also help guide the placement of the needle during the biopsy.
- Monitor the thyroid gland and nodules over time
Fine Need Aspiration Biopsy (FNA)
As the name suggests, a healthcare professional will insert a thin needle into the thyroid gland. They will then remove a small amount of fluid or tissue from the nodule. The collected cells will be examined by a pathologist to determine if the nodules are cancerous or not.
To report the results of the biopsy, a standardized system known as the Bethesda System will be used. With each finding, the associated risk of cancer is assigned. The results will generally be reported in the following manner:
- Unsatisfactory or non-diagnostic – this was when there were too few cells collected to make a proper diagnosis. A risk of 5% to 10% of cancer is assigned. A repeat FNA will generally need to be carried out.
- Benign – the cells show a risk of 0 to 3% for cancer.
- Atypia or follicular lesion of undetermined significance – the cancer risk is between 10% and 30%.
- Follicular lesion – this is cancerous 25% to 40% of the time.
- FLUS, AUS, and follicular lesion of indeterminate results – this is when there were enough cells present in the sample to be examined, but a reliable diagnosis could not be provided.
- Suspicious for malignancy – this will have a cancer risk of 50% to 75%.
A second biopsy might be required depending on the initial results. Surgery may also be required.
If the results of the biopsy are unclear or indeterminate, genetic testing of the cells can be performed. This will help to detect any cancer-causing mutations in the genetic material of the cells. Genetic testing panels are available to determine if the nodule is cancerous. These tests will also help determine if surgery is required.
Molecular tests have been recognized by the American Thyroid Association as useful supplemental information. They are recommended but should be used with caution. They should also not replace ultrasounds and other clinical findings or clinical judgment. It is important to note that the absence of mutated genes associated with thyroid cancer does not exclude the possibility completely.
This is a blood test that is not regularly used for evaluating these nodules. However, it can be ordered to determine if the thyroid gland is producing excess calcitonin. Elevated levels are used as an indicator of C-cell hyperplasia, but other procedures will be used to finalize the diagnosis.
This scan is used to evaluate the thyroid gland. Its ability to detect cancer is still being studied. The scan will use a small volume of radioactively labeled glucose and follow up testing may be done depending on the results.
Radioactive Iodine Scan
This scan is not carried out regularly anymore because the FNA and ultrasound will be better at evaluating the thyroid nodules. However, this can still be done in rare cases when a person has both thyroid nodules and hyperthyroidism. A nodule that produces excess thyroid hormones will take up more radioactively labeled iodine than the normal thyroid tissue. This will show up on the scan.