How is Thyroid Cancer Diagnosed?
Prompt attention to signs and symptoms is the best approach to early diagnosis of most thyroid cancers. Thyroid cancer can cause any of the following local signs or symptoms:
- a lump in the neck, sometimes growing rapidly
- a pain in the front of the neck, sometimes going up to the ears
- hoarseness or voice change which does not go away
- trouble swallowing
- breathing problems (feeling as if one were "breathing through a straw")
- a cough that continues and is not due to a cold
If you have any of these signs or symptoms, talk to your doctor right away. Other cancers of the neck area and many noncancerous conditions can cause some of the same symptoms. Thyroid nodules are common, and they are usually benign. But the only way to find out if these symptoms are due to a thyroid cancer, some other cancer, or a benign condition is to have a medical evaluation. The sooner you receive a correct diagnosis, the sooner you can start treatment and the more effective your treatment will be.
History and Physical Examination
If you have any signs or symptoms that suggest you might have thyroid cancer, the first step toward arriving at a diagnosis is for your health care professional to take a complete medical history. This is an interview in which you will be asked questions about your risk factors, symptoms, and any other health problems or concerns. If someone in your family has had thyroid cancer (especially medullary thyroid cancer) or adrenal gland tumors called pheochromocytomas, it is important to tell your doctor.
A physical exam will provide other information about signs of thyroid cancer and other health problems. During your physical exam, your doctor will pay special attention to the size and firmness of your thyroid and any enlarged lymph nodes in your neck.
Fine Needle Aspiration Biopsy
The simplest way to test whether a thyroid lump or nodule is cancerous is with a fine needle aspiration (FNA) of the thyroid nodule. This type of biopsy can usually be done in your doctor's office or clinic. Local anesthesia (numbing medication) may be injected into the skin over the nodule, but in some cases an anesthetic may not be needed at all. The major complication is bleeding, but this is rare except in people with bleeding disorders. Be sure to tell your doctor is you have a bleeding disorder.
Your doctor will place a thin needle directly into the nodule for about 10 seconds and withdraws cells and a few drops of fluid. The doctor usually repeats this procedure 2 or 3 times during the same appointment to take samples from several areas of the nodule. The cells can then be viewed under a microscope to see if they appear cancerous or benign.
This test is generally done on all thyroid nodules that are large enough to be felt. Sometimes FNA tests are done with ultrasound machines to help guide the needle into nodules that are otherwise too small to be felt. FNA can help your doctor decide if surgery or other tests are needed.
About 1 test in every 10 will need to be repeated on another day. Of every 10 FNA tests, up to 8 clearly show that the nodule is benign. Cancer is clearly shown in only 1 of every 20 FNA tests. Some test results are classified as "suspicious" or "atypical" because the FNA findings do not clearly show whether the nodule is benign or malignant. In these cases, additional tests such as a diagnostic surgical lobectomy (i.e. removal of the gland on one side of the windpipe) may be needed, particularly if the doctor thinks the nodule is cancerous.
A new way of testing the thyroid cells is by examining their genetic profile. This is too new to be used in most situations, but may play a role in the future.
Imaging Tests
Thyroid scan: For this test, a small amount of radioactive iodine is taken by mouth or injected into a vein. The body concentrates these radioactive chemicals in the thyroid gland, and a special camera placed in front of your neck then measures the amount of radiation in the gland. Abnormal areas of the thyroid that contain less radioactivity than the surrounding tissue are called cold nodules, and nodules that take up more radiation are called hot nodules.
Most thyroid nodules appear as cold nodules on thyroid scans. Because both benign and cancerous nodules can appear cold, this test is usually not very helpful in diagnosing thyroid cancer. However, once a biopsy has determined that a thyroid cancer is present, scans are very useful in follow-up for potential spread. Scans following initial surgical treatment can also help assess how far a thyroid cancer has initially spread, if at all.
If the entire thyroid gland is removed for cancer, repeated thyroid scans will be done. The test becomes more sensitive in this instance because more of the injected radioactive iodine enters thyroid cancer cells. Radioiodine scans are frequently used in the care and management of patients with differentiated (papillary and follicular and Hurthle cell) thyroid cancer. Because MTC cells do not take up iodine, radioiodine scans are not used in this cancer.
Radioiodine thyroid scans are most accurate if patients have high blood levels of thyroid-stimulating hormone (TSH, or thyrotropin). In the past, the only way to increase TSH levels in patients whose thyroid glands had been surgically removed was to stop thyroid hormone pills 2 to 6 weeks before treatment. This lowers thyroid hormone levels (a condition known as hypothyroidism) and causes the pituitary gland to release more TSH, which in turn stimulates the cancer cells to take up the radioactive iodine. Although this intentional hypothyroidism is temporary, it is sometimes uncomfortable for the patient. Symptoms include tiredness, depression, some weight gain, sleepiness, constipation, muscle aches, and reduced concentration, in addition to other conditions. An injectable form of thyrotropin is now available that can increase patients' TSH levels before radioiodine scanning so that withholding thyroid hormone replacement is not necessary.
Ultrasound: Ultrasound, or ultrasonography, uses sound waves to create images of your body. A transducer held near your thyroid gland gives off high-frequency sound waves and detects echoes that bounce off thyroid tissue. Normal thyroid tissue and most thyroid nodules make different echo patterns. These echo patterns are processed by a computer to create a picture of the thyroid gland. This test can be used to check the number and size of thyroid nodules. However, thyroid cancers and most benign nodules look the same on ultrasound studies, so this test is not done routinely.
Computed tomography (CT or CT scan): The CT scan is an x-ray procedure that produces detailed cross-sectional images of your body. Instead of taking one picture, as does a normal x-ray, a CT scanner takes many pictures of the part of your body being studied as it rotates around you. A computer then combines these pictures into an image of a slice of your body. A CT scan isn聮t usually used to diagnose thyroid cancer, but might be used to see if a known thyroid cancer has spread.
Magnetic resonance imaging (MRI or MRI scan): MRI scans use radio waves and strong magnets instead of x-rays. The energy from the radio waves is absorbed and then released in a pattern formed by the type of tissue and by certain diseases. A computer translates the pattern of radio waves given off by the tissues into a very detailed image of parts of the body. A contrast material might be injected just as with CT scans. MRI scans are very helpful in looking at cancers. Sometimes they can tell a benign tumor from a malignant one.
MRI scans take longer than CT scans – often up to an hour. Also, you have to lie inside a narrow tube, which is confining and can upset people with a fear of enclosed spaces. The machine makes a thumping noise, and some facilities provide headphones with music to block out the noise. However the benefits of the test outweigh any discomfort.
MRI and CT scans can reveal tumors within a thyroid gland but may also determine the size of the tumor, whether it is growing into nearby tissues, and if it has spread to lymph nodes in the neck or distant structures.
Octreotide scan: Sometimes an octreotide scan, which uses a radioactively tagged hormone, may be done to evaluate the spread of medullary thyroid cancer.
Positron emission tomography (PET): Positron emission tomography (PET) uses glucose (a form of sugar) that contains a radioactive atom. Cancer cells in the body absorb large amounts of the radioactive sugar and a special camera can detect the radioactivity. This can be a very important test if your thyroid cancer is one that doesn聮t take up radioactive iodine. In this situation, the PET scan may be able to tell if the cancer has spread. Newer techniques and devices can combine a CT scan and a PET scan to even better pinpoint tumor spread.
Blood Tests
No blood test can tell whether a thyroid nodule is cancerous. However, testing your blood levels of thyroid-stimulating hormone (TSH) may be useful in checking the overall activity of your thyroid gland. If medullary thyroid carcinoma (MTC) is suspected, a blood calcitonin test will be done. This test can help tell if MTC is present.
Thyroglobulin is a protein manufactured by the thyroid gland. Its measurement cannot be used to diagnose thyroid cancer. However, after the removal of most of the thyroid by surgery and ablation of residual normal cells by radioactive iodine, its level in the blood should be very low. If it is not low, this might mean that thyroid cancer is still present. If the level rises, it is a sign that the cancer may be coming back. (from American Cancer Society)
How is Thyroid Cancer Diagnosed?
