Diagnosing Thyroid Cancer
Thyroid cancer may be diagnosed after a person goes to a doctor because of symptoms, or it might be found during a routine physical exam or other tests. If there is a reason to suspect you might have thyroid cancer, your doctor will use one or more tests to confirm the diagnosis.
This would include:
–Family History and Physical Exam
–Imaging tests may be done for a number of reasons:
- To help find suspicious areas that might be cancer
- To learn how far cancer may have spread
- To help determine if treatment is working
People who have or may have thyroid cancer will get one or more of these tests.
-Ultrasound
Ultrasound uses sound waves to create images of parts of your body. You are not exposed to radiation during this test.
This test can help determine if a thyroid nodule is solid or filled with fluid. (Solid nodules are more likely to be cancerous.) It can also be used to check the number and size of thyroid nodules as well as help determine if any nearby lymph nodes are enlarged because the thyroid cancer has spread.
For thyroid nodules that are too small to feel, this test can be used to guide a biopsy needle into the nodule to get a sample. Even when a nodule is large enough to feel, most doctors prefer to use ultrasound to guide the needle.
Radioiodine scan
Radioiodine scans can be used to help determine if someone with a lump in the neck might have thyroid cancer. They are also often used in people who have already been diagnosed with differentiated (papillary, follicular, or Hürthle cell) thyroid cancer to help show if it has spread. Because medullary thyroid cancer cells do not absorb iodine, radioiodine scans are not used for this cancer.
For this test, a small amount of radioactive iodine (called I-131) is swallowed (usually as a pill) or injected into a vein. Over time, the iodine is absorbed by the thyroid gland (or thyroid cells anywhere in the body). A special camera is used several hours later to see where the radioactivity is.
For a thyroid scan, the camera is placed in front of your neck to measure the amount of radiation in the gland. Abnormal areas of the thyroid that have less radioactivity than the surrounding tissue are called cold nodules, and areas that take up more radiation are called hot nodules. Hot nodules usually are not cancerous, but cold nodules can be benign or cancerous. Because both benign and cancerous nodules can appear cold, this test by itself can’t diagnose thyroid cancer.
After surgery for thyroid cancer, whole-body radioiodine scans are useful to look for possible spread throughout the body. These scans become even more sensitive if the entire thyroid gland has been removed by surgery because more of the radioactive iodine is picked up by any remaining thyroid cancer cells.
Radioiodine scans work best if patients have high blood levels of thyroid-stimulating hormone (TSH, or thyrotropin). For people whose thyroid has been removed, TSH levels can be increased by stopping thyroid hormone pills for a few weeks before the test. This leads to low thyroid hormone levels (hypothyroidism) and causes the pituitary gland to release more TSH, which in turn stimulates any thyroid cancer cells to take up the radioactive iodine. A downside of this is that it can cause the symptoms of hypothyroidism, including tiredness, depression, weight gain, sleepiness, constipation, muscle aches, and reduced concentration. One way to raise TSH levels without withholding thyroid hormone is to give an injectable form of thyrotropin (Thyrogen®) before the scan.
Because any iodine already in the body can affect this test, people are usually told to avoid foods or medicines that contain iodine for a few days before the scan.
Radioactive iodine can also be used to treat differentiated thyroid cancer, but it is given in much higher doses. This type of treatment is described in Radioactive iodine (radioiodine) therapy.
Chest x-ray
If you have been diagnosed with thyroid cancer (especially follicular thyroid cancer), a plain x-ray of your chest may be done to see if cancer has spread to your lungs.
Computed tomography (CT) scan
The CT scan is an x-ray test that makes detailed cross-sectional images of your body. It can help determine the location and size of thyroid cancers and whether they have spread to nearby areas, although ultrasound is usually the test of choice. A CT scan can also be used to look for spread into distant organs such as the lungs.
One problem using CT scans is that the CT contrast dye contains iodine, which interferes with radioiodine scans. For this reason, many doctors prefer MRI scans for differentiated thyroid cancer.
Magnetic resonance imaging (MRI) scan
MRI scans use magnets instead of radiation to create detailed cross-sectional images of your body. A MRI can be used to look for cancer in the thyroid, or cancer that has spread to nearby or distant parts of the body. But ultrasound is usually the first choice for looking at the thyroid. MRI can provide very detailed images of soft tissues such as the thyroid gland. MRI scans are also very helpful in looking at the brain and spinal cord.
Positron emission tomography (PET) scan
A PET scan can be very useful if your thyroid cancer is one that doesn’t take up radioactive iodine. In this situation, the PET scan may be able to tell whether the cancer has spread.
Biopsy
The actual diagnosis of thyroid cancer is made with a biopsy, in which cells from the suspicious area are removed and looked at in the lab.