Fine-Needle Aspiration Biopsy of the Thyroid

Doctors use fine-needle aspiration biopsy of the thyroid to treat thyroid cysts or detect cancer in a thyroid nodule.

The thyroid gland is found in the neck below the "Adam’s apple." It produces thyroid hormone, which stimulates the body’s metabolism. Thyroid nodules are common, especially as we age. Many are found incidentally during routine examinations or radiology testing. Women are more likely to have nodules, increasing their risk of detected cancer. However, each nodule is more likely to be cancerous in men.

Doctors are concerned when a new growth is detected, regardless of the tissue involved. They want to determine whether the growth is cancerous. Fortunately, fewer than 10% of thyroid nodules are malignant. Adenomas are harmless growths contained within a capsule. Even though cancerous nodules are uncommon, doctors take the necessary measures to ensure certainty.

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 nodule’s onset, related pain or discomfort, symptoms of thyroid disease, and family history are addressed. Factors like age, sex, and history of head and neck radiation increase the suspicion of malignancy. The doctor evaluates the size, characteristics, and mobility of the nodule, as well as associated lymph nodes. The evaluation helps determine if further investigations are necessary.

The following factors increase the suspicion of malignancy:

• Patients less than 30 years of age and greater than 60 years of age have a higher risk of cancer in a thyroid nodule;
• 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 if they are one of many in the gland or hyperfunctioning.

After the initial evaluation, the doctor may order thyroid blood tests or imaging scans to determine the functional activity and anatomy of the 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.

QUESTION

Why do doctors perform a fine-needle aspiration biopsy (FNAB) of the thyroid gland?

A biopsy to obtain tissue is the best technique for detecting or ruling out cancer. Fine-needle aspiration biopsy has become the method of choice for obtaining samples of thyroid tissue. When performed properly, it has a false-negative rate of less than 5%. The procedure is also performed to treat thyroid cysts. Aspiration of the cyst can shrink the swelling and analyze the fluid for cancer.

Should fine-needle aspiration biopsy be done on all thyroid nodules?

There are certain situations in which a biopsy may not be necessary, such as in patients with overactive thyroids or "hot" nodules. Fine-needle aspiration biopsy may be done to diagnose a nodule, select therapy, drain a cyst, or inject medication to shrink a recurrent cyst.

How is a fine-needle aspiration biopsy performed?

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. Little patient preparation is required. After the examination, the patient lies down and the neck is exposed. The area is cleaned with iodine. A local anesthetic may be injected, although it is often unnecessary. A small needle is inserted into the nodule to obtain tissue. The procedure is repeated four to six times. Pressure is then applied to minimize bleeding and swelling. The entire procedure usually takes less than 20 minutes.

How long does it take to get the results of a fine-needle aspiration biopsy of the thyroid?

The results are generally available within 1 week and help determine further interventions or treatments.

What happens to the thyroid tissue obtained during a fine-needle aspiration biopsy?

The obtained tissue is prepared onto glass slides and sent to the pathologist for evaluation. The chance of a false-negative test varies from 0%-5%, while the chance of a false positive is less than 5%. The pathologist’s report helps determine further treatment based on the results.

What are the complications of a fine-needle aspiration biopsy of the thyroid?

Most patients experience minimal bleeding or swelling. Discomfort is usually relieved with acetaminophen. Complications like bleeding, infection, and cyst formation are rare. Patients should contact their doctor if they notice excessive bruising or swelling, persistent pain, or develop a fever.

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