Saturday, September 4, 2010

Thyroid Cancer: Testing & Diagnosis

If you have any signs or symptoms that suggest you might have thyroid cancer, your health care professional will want to take a complete medical history. You will be asked questions about your possible risk factors, symptoms, and any other health problems or concerns.

Medical history and physical exam: 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 as this might indicate you are at high risk for this disease. A physical exam will give more information about signs of thyroid cancer and other health problems. During the exam, your doctor will pay special attention to the size and firmness of your thyroid and any enlarged lymph nodes in your neck.

 Blood Tests:
  • Thyroid stimulating hormone (TSH) :  No blood test can tell whether a thyroid nodule is cancerous. However, tests of blood levels of thyroid-stimulating hormone (TSH or thyrotropin) may be used to check the overall activity of your thyroid gland.
This information can be used to help choose imaging tests (ultrasound or nuclear scans) for the initial evaluation of a thyroid nodule. Levels of thyroid hormones (T3 and T4) may also be measured to get a sense of thyroid gland function.
  • Thyroglobulin: Thyroglobulin is a protein made by the thyroid gland. Its measurement in the blood cannot be used to diagnose thyroid cancer. But it can be helpful after treatment. 
A common way to treat thyroid cancer is to remove most of the thyroid by surgery and then use radioactive iodine (using the high doses for treatment) to destroy any remaining thyroid cells.

These treatments should lead to a very low level of thyroglobulin in the blood. If it is not low, this might mean that thyroid cancer is still present. If the level rises again after being low, it is a sign that the cancer may be coming back.
  • Calcitonin: If medullary thyroid carcinoma (MTC) is suspected or if you have a family history of the disease, blood tests for calcitonin levels can help tell whether MTC might be present. This test is also useful to look for the possible recurrence after treatment of MTC. Because calcitonin can affect blood calcium levels, these may be checked as well.
  • Carcinoembryonic antigen (CEA): People with MTC often have high blood levels of a protein called carcinoembryonic antigen (CEA). Tests for CEA can sometimes help tell if cancer is present.
  • Other tests: You may have other blood tests as well. For example, if you are scheduled for surgery, tests will be done to check your blood cell counts, to look for bleeding disorders, and to check the function of your liver and kidneys.
Diagnostic Radiology:
  • Ultrasound: Ultrasound, or sonography, uses sound waves to create images of your body. For this test, a small, microphone-like instrument called a transducer is placed on the skin in front of your thyroid gland. It gives off sound waves and picks up the echoes as they bounce off the thyroid. The echoes are converted by a computer into a black and white image that is displayed on a computer screen. You are not exposed to radiation during this test.
This test is helpful in determining if a thyroid nodule is solid or filled with fluid. It can also be used to check the number and size of thyroid nodules. Ultrasound features can sometimes suggest a nodule is likely to be a cancer, but ultrasound can't tell for sure. 

For thyroid nodules that are too small to be felt, this test can be used to guide a biopsy needle into the nodule to obtain a sample. Even when a nodule is large enough to feel, some doctors prefer to use ultrasound to guide the needle.

Ultrasound can also help determine whether any nearby lymph nodes are enlarged because the thyroid cancer has spread. Many thyroid specialists recommend ultrasound for all patients with thyroid nodules large enough to be felt.
  • Chest X-Ray: A plain x-ray of your chest may be done to see if cancer has spread to your lungs, especially if you have follicular thyroid cancer.
  • Imaging Tests: Imaging tests may be done for a number of reasons, including to find out whether a suspicious area might be cancerous, to learn how far the cancer may have spread, and to help determine if treatment has been effective.
  • Computed tomography: The computed tomography (CT or CAT) scan is an x-ray test that produces detailed cross-sectional images of your body. Instead of taking one picture, like a regular x-ray, a CT scanner takes many pictures as it rotates around you while you lie on a table. A computer then combines these pictures into images of slices of the part of your body being studied. Unlike a regular x-ray, a CT scan creates images of the soft tissues in the body.
You may be asked to drink a contrast solution or receive an IV (intravenous) line through which a different contrast dye is injected. This helps better outline structures in your body.

The injection may cause some flushing (a feeling of warmth, especially in the face). Some people are allergic and get hives. Rarely, more serious reactions like trouble breathing or low blood pressure can occur. Be sure to tell the doctor if you have ever had a reaction to any contrast material used for x-rays.

CT scans take longer than regular x-rays. You need to lie still on a table while they are being done. During the test, the table moves in and out of the scanner, a ring-shaped machine that completely surrounds the table. You might feel a bit confined by the ring you have to lie in while the pictures are being taken.

The CT scan 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.

In some cases, a CT scan can be used to guide a biopsy needle precisely into a suspected area of cancer spread. For a CT-guided needle biopsy, you remain on the CT scanning table, while a radiologist advances a biopsy needle toward the location of the mass. CT scans are repeated until the doctors can see that the needle is within the mass. A biopsy sample is then removed and looked at under a microscope.

One disadvantage of CT scans for differentiated thyroid cancer is that the CT contrast dye contains iodine, which interferes with radioiodine scans. For this reason, many doctors prefer MRI scans instead of CT scans.
  • Magnetic Resonance Imaging or MRI:  Like CT scans, magnetic resonance imaging (MRI) scans 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 particularly helpful in looking at the brain and spinal cord.
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 body tissue and by certain diseases. A computer translates the pattern into a very detailed image of parts of the body. A contrast material called gadolinium is often injected into a vein before the scan to better see details.

MRI scans are a little more uncomfortable than CT scans. First, they take longer -- often up to an hour. Second, you have to lie inside a narrow tube, which is confining and can upset people with claustrophobia (a fear of enclosed spaces).Special, "open" MRI machines can sometimes help with this if needed. The machine also makes buzzing and clicking noises that you may find disturbing. Some centers provide headphones with music to block this noise out.
  • Nuclear Medicine Scans: Nuclear medicine (radionuclide) scans involve putting substances with small amounts of radiation into the body and then detecting where the substances go with special cameras. These tests can help locate cells in the body that are not behaving normally, although they don't provide very detailed images.
Pathology Evaluation:
  • Biopsy: The actual diagnosis of thyroid cancer is made from the results of a biopsy, in which cells from the suspicious area are removed and looked at under a microscope. The simplest way to find out if 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. Your doctor will place a thin, hollow needle directly into the nodule to take out (aspirate) cells and a few drops of fluid into a syringe. 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 looked at under a microscope to see if they look cancerous or benign.

Before the biopsy, local anesthesia (numbing medicine) may be injected into the skin over the nodule, but in some cases an anesthetic may not be needed at all. A potential complication of the biopsy is prolonged bleeding, but this is rare except in people with bleeding disorders. Be sure to tell your doctor if you have a bleeding disorder.

This test is generally done on all thyroid nodules that are big enough to be felt. This means that they are larger than about 1 centimeter (about 1/2 inch) across. If a nodule is too small for the doctor to feel, sometimes FNA biopsies can be done using an ultrasound machine to help the doctor find the right place to put the needle. 

About 2 tests in every 10 may need to be repeated because the sample ends up not containing enough cells. About 7 of 10 FNA biopsies will show that the nodule is benign. Cancer is clearly diagnosed in only 1 of every 20 FNA biopsies.

Sometimes the test results come back as suspicious or atypical. This happens when the FNA findings can't show for sure if the nodule is benign or malignant. In these cases, a more involved biopsy may be needed to get a better sample, particularly if the doctor has reason to think the nodule may be cancerous.

This might include a biopsy using a larger needle or a surgical "open" biopsy or a lobectomy (removal of the gland on one side of the windpipe). Surgical biopsies are done in an operating room while you are under general anesthesia (in a deep sleep).

Nuclear Medicine: 
  • Radioiodine Scan: For this test, a small amount of radioactive iodine (called I-131) is swallowed (usually as a pill) or injected into a vein. Radioactive iodine is also used to treat differentiated thyroid cancer (papillary, follicular, and Hurthle cell), but in much higher doses. The iodine is absorbed by the thyroid gland (or thyroid cells anywhere in the body) over time, and a special camera is used several hours later to see where the radioactivity has gone.
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 contain 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 either benign or cancerous. Because both benign and cancerous nodules can appear cold, this test by itself can't diagnose thyroid cancer.

Radioiodine scans are often used in the care and management of patients with differentiated thyroid cancer. Because medullary thyroid cancer cells do not take up iodine, radioiodine scans are not used for this cancer.

If a biopsy has determined that a thyroid cancer is present, whole-body radioiodine scans are very useful to follow-up potential spread throughout the body from differentiated thyroid cancers. Scans after surgery can also help determine how far a thyroid cancer has spread, if at all.

If the entire thyroid gland has been removed because of cancer, radioiodine scans may be done frequently. The scan becomes more sensitive in this instance because more of the radioactive iodine is picked up by thyroid cancer cells that have spread elsewhere.

Radioiodine scans work best if patients have high blood levels of thyroid-stimulating hormone (TSH, or thyrotropin). TSH levels may be increased by stopping thyroid hormone pills for a few days to a few weeks before the test.

This lowers thyroid hormone levels 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 can cause symptoms like tiredness, depression, weight gain, sleepiness, constipation, muscle aches, and reduced concentration.

An injectable form of thyrotropin is now available that can increase patients' TSH levels before radioiodine scanning, so withholding thyroid hormone for a long period of time may not be necessary.

Because iodine that is already in the body can interfere with this test, people are usually told not to ingest foods or medicines that contain iodine in the days before the scan.
  • Positron Emission Tomography: For a positron emission tomography (PET) scan, glucose (a form of sugar) that contains a radioactive atom is injected into the blood. Because cancer cells in the body are growing rapidly, they absorb large amounts of the radioactive sugar. A special camera can then create a picture of areas of radioactivity in the body.
This test 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.

PET scans do not show anatomical details as clearly as a CT or MRI, but some newer machines are able to perform both a PET and CT scan at the same time (PET/CT scan). This lets the doctor see areas that "light up" on the PET scan in more detail.
  • Octreotide Scan: Sometimes an octreotide scan, which uses a radioactively tagged hormone, may be done to look for the spread of medullary thyroid cancer. These cancers don't take up iodine, so radioiodine scans can't be used for them.
Last Revised: 07/20/2010

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