- Thyroid Nodules
- Why Do It?
- When to Do an FNAB
- Procedural Steps
- When to Expect Results
Facts you should know about a fine-needle aspiration biopsy
- Fine-needle aspiration biopsy (FNAB) of the thyroid is a procedure used to detect cancer in a thyroid nodule or to treat thyroid cysts.
- The chance that a thyroid nodule is malignant varies with age, gender, radiation exposure, and other factors.
- fine needle aspiration biopsy is performed in a doctor's office and takes about 20 minutes.
- Complications are rare, but include bleeding, bruising, and infection.
- Results help determine further management and treatment and are usually available within a week.
What are thyroid nodules?
The thyroid gland is found in the neck just below the "Adam's apple." This gland is responsible for producing thyroid hormone, which is an important hormone that stimulates the metabolism of the body. Thyroid nodules are so common that up to half of all people have one, without any symptoms or effect. Like many things, the thyroid gland gets "lumpier" as we get older and the frequency of these nodules increases with age. In fact, many are found incidentally during routine examinations or radiology testing. Thyroid nodules are also more common in women than in men. Interestingly, because women have so many more nodules than men, the incidence of detected cancer is higher in women than in men by virtue of absolute numbers. However, each individual nodule is more likely to be cancerous if found in a man.
Doctors always hold a degree of concern whenever a new growth is detected on the body, regardless of the tissue involved. The concern is whether or not the growth or nodule is cancer. Fortunately, fewer than 10% of thyroid nodules are malignant. The majority of thyroid nodules are harmless growths, known as adenomas, and are contained within a capsule. Even though cancerous nodules are uncommon, the doctor will take the necessary measures to be certain.
What is the initial assessment of a thyroid nodule?
All patients with a thyroid nodule should undergo a complete medical history and physical examination. Specific questions regarding the onset of the nodule, related pain or discomfort, symptoms of thyroid disease, and family history are addressed. In addition, the doctor will take into account the patient's age and sex when evaluating the possibility of malignancy. Patients with a history of head and neck radiation (which was commonly used in the 1950's as an acne treatment) are at a higher risk. Cancerous nodules are also more frequent in men as compared to women. The doctor will also look for general symptoms of thyroid disease in addition to other illnesses. The size and characteristics of the nodule are assessed. Is it soft or firm? Does it move with swallowing, or is it fixed? Is there more than one nodule? Are there other nodes involved? Does it hurt when the nodule is touched? The answers to these questions will help the doctor evaluate what further investigations, if any, are necessary.
The following is a list of factors that increase the suspicion of malignancy:
- Age: Patients less than 30 years of age and greater than 60 years of age have a higher risk of cancer in a thyroid nodule as do children;
- Associated symptoms such as difficulty swallowing or hoarseness;
- History of head and neck irradiation;
- A hard, fixed nodule on examination;
- Surrounding enlarged lymph nodes; and
- Previous history of thyroid cancer in the family.
Nodules are less concerning to a physician if it is one of many present in the gland, and also if the nodule is hyperfunctioning (or "hot") using nuclear thyroid imaging.
After the initial evaluation, the doctor may choose to order thyroid blood tests or imaging scans to determine the functional activity of a thyroid nodule and its anatomy. The cornerstone in the assessment of a solitary thyroid nodule is a procedure known as fine needle aspiration biopsy ("FNAB") of the thyroid gland.
Why do doctors perform a fine-needle aspiration biopsy (FNAB) of the thyroid gland?
A biopsy to obtain tissue for analysis is the best technique for detecting or ruling out the presence of cancer. For many years, a core biopsy of the thyroid was the procedure of choice. This method involved a large biopsy, which was often more difficult for patients. Fine-needle aspiration biopsy has now become the method of choice for obtaining samples of thyroid tissue. The procedure is technically quite simple. When performed properly, the testing has a false-negative rate of less than 5%. This means that a positive finding, such as cancer, will be missed fewer than five times out of 100.
The fine-needle aspiration is also performed to treat thyroid cysts. A thyroid cyst is a fluid-filled sac within the thyroid gland. Aspiration of the cyst with a needle and syringe can shrink the swelling from the cyst and the fluid removed can be analyzed for cancer.
Should fine-needle aspiration biopsy be done on all thyroid nodules?
There are certain situations in which your physician may elect not to perform a biopsy of a nodule. For example, in a patient with an overactive thyroid (hyperthyroidism), the chance for a nodule to be cancerous is significantly less, particularly if other studies (such as nuclear thyroid imaging) show that the nodule is producing thyroid hormone (a "hot" nodule).
A doctor may recommend fine-needle aspiration biopsy of the thyroid in the following situations:
How do doctors perform a fine-needle aspiration biopsy?
In most cases, if the nodule can be felt, a biopsy can be performed in the doctor's office. In some cases, an ultrasound may be needed to help guide the biopsy, (for example, if the nodule cannot be felt without difficulty or if the nodule has areas within it that specifically should be biopsied).
Little preparation by the patient is required. There is no need to fast or to withhold medications on the day of the biopsy. Occasionally, though, a patient may be asked not to take blood-thinning medication either before or on the day of the biopsy. After an examination to pinpoint the nodule, the patient is asked to lie down and the neck is exposed. Depending on the location of the nodule and the type of clothes the patient is wearing, he or she may be asked to change into a gown. The doctor drapes the area around the neck and cleans the neck off. This is usually done with iodine, which is a brown liquid that sterilizes the skin. Some doctors may choose to inject a local anesthetic. Often, the injection of the anesthetic results in an initial discomfort, like a bee sting. The majority of doctors who regularly perform fine needle aspiration biopsies of the thyroid do not use a local anesthetic for this reason. Since the needle used for fine-needle aspiration biopsy is so fine, anesthesia often results in simply another uncomfortable poke for the patient. If a patient is particularly concerned and nervous, a topical anesthetic preparation may be applied, which takes 10 to 20 minutes to work, thus prolonging the procedure. A patient undergoing fine-needle aspiration biopsy should discuss any preferences for local anesthetic before the procedure begins. Most patients undergoing fine-needle aspiration biopsy forego the use of any anesthetic and do very well.
Once the patient is ready, a small, fine-gauge needle is inserted into the nodule. The needle is smaller in diameter than the needle used in most blood draws (usually a 25 gauge 1.5-inch needle). The patient holds his breath while the needle is rocked gently to obtain as much tissue as possible. (The reason for holding the breath is to minimize movement of the structures in the neck.) The needle is then withdrawn and pressure is applied over the thyroid area to minimize bleeding. This procedure is usually repeated four to six times to ensure that an adequate amount of tissue has been collected. After the procedure, pressure is applied over the neck area for 5 to 10 minutes to assure that the bleeding has stopped. The pressure also helps to reduce any swelling that may occur. The entire procedure usually takes less than 20 minutes.
What are the complications of a fine-needle aspiration biopsy of the thyroid?
Most patients notice very little bleeding or swelling. There may be some discomfort in the area for a few hours after the biopsy, which is usually relieved with acetaminophen (Tylenol). Some patients like to put an ice pack over the area when they get home, but most do well without such measures. The risks of fine-needle aspiration biopsy of the thyroid include bleeding, infection, and cyst formation, but these complications are exceedingly rare. Patients should contact their doctor if they notice any excessive bruising or swelling in the area of the biopsy, if they have persistent pain in the area, or if they develop a fever.
What happens to the thyroid tissue obtained during a fine-needle aspiration biopsy?
After the procedure, the tissue obtained is prepared onto glass slides and sent to the pathologist for evaluation. First, the pathologist determines whether or not enough thyroid tissue has been obtained for analysis. (When there is an insufficient amount, a repeat fine needle aspiration biopsy is necessary.) After analysis, the tissue is classified. Although the classifications used by pathologists vary, the tissue is usually reported as (1) benign; (2) malignant; (3) suspicious; or (4) indeterminate. The chance of a false-negative test (a test report that is negative when cancer is actually present) varies from 0%-5%, depending on where the test is performed. The chance of a false positive (a test report showing cancer when there is no cancer present) is less than 5% and is usually due to the presence of degenerating cells or atypical cells. These results are reported back to the doctor's office, usually within 1 week. At this point, the doctor discusses the implications of the report and outlines further treatment, if needed based on the results.
How long does it take to get the results of a fine-needle aspiration biopsy of the thyroid?
A fine-needle aspiration biopsy of the thyroid gland is an effective method to determine whether or not a thyroid nodule is cancer. The procedure is relatively simple procedure that is usually performed in a doctor's office and usually takes less than 20 minutes. Complications are rare but include bleeding, bruising, and infection. Results are generally available within 1 week and help determine what further interventions or treatments are needed.
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Ross, Douglas S. "Thyroid biopsy." UptoDate. Apr. 6, 2020. <http://www.uptodate.com/contents/thyroid-biopsy?source=search_result&search=thyroid+biopsy&selectedTitle=1~29>.