Fine-Needle Aspiration Biopsy of the Thyroid
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. Between 4% and 7% of people in the United States have lumps (or nodules) in their thyroid gland that can be felt on examination. Like many things, the thyroid gland gets "lumpier" as we get older and the frequency of these nodules increases with age. Thyroid nodules are also more common in women than in men. In fact, ultrasound studies have found that up to 1 in every 3 women has at least one thyroid nodule that may be too small to notice. (Usually, a nodule needs to be greater than 1centimeter in diameter for it to be felt.)
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 (malignant). 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 for acne ) 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 20 years of age and greater than 70 years of age have a higher risk of cancer in a thyroid nodule;
- Gender: Men have a higher risk than women;
- Associated symptoms such as difficulty swallowing or hoarseness ;
- History of head and neck irradiation;
- A hard, fixed nodule;
- Surrounding enlarged lymph nodes; and
- Previous history of thyroid cancer .
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. The cornerstone in the assessment of a solitary thyroid nodule is a procedure known as fine-needle aspiration biopsy ("FNAB") of the thyroid gland.
Fine-needle aspiration biopsy (FNAB) of the thyroid gland - why is it done?
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. FNAB 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 5 times out of 100.
Should FNAB be done on all thyroid nodules?
There are certain cases in which your physician may elect not to perform a biopsy of a nodule. For example, in a patient with an over- active thyroid ( hyperthyroidism ), the chance for a nodule to be cancerous is significantly less, particularly if other studies (such as radionucleotide imaging) show that the nodule is producing thyroid hormone (a "hot" nodule).
A doctor may recommend FNAB of the thyroid in the following situations: - To make a diagnosis of a thyroid nodule;
- To help select therapy for a thyroid nodule;
- To drain a cyst that may be causing pain; or
- To inject a medication to shrink a recurrent cyst.
How is FNAB performed?
FNAB is performed in a doctor's office. 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 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 FNABs of the thyroid do not use a local anesthetic for this reason. Since the needle used for FNAB 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 FNAB should discuss any preferences for local anesthetic before the procedure begins. Most patients undergoing FNAB 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 4 to 6 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 FNAB 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 FNAB 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 at the FNAB?
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 FNAB 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. These results are reported back to the doctor's office, usually within one week. At this point, the doctor discusses the implications of the report and outlines further treatment, if needed based on the results.
Summary
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 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. - Fine-needle aspiration biopsy (FNAB) of the thyroid is a procedure used to detect cancer in a thyroid nodule or to treat thyroid cysts.
- Between 4% and 7% of people in the United States have thyroid nodules.
- The chance that a thyroid nodule is malignant varies with age, gender, radiation exposure, and other factors.
- FNAB 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.
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