Fine Needle Aspiration Biopsy of the Thyroid (FNAB) Procedure Information on MedicineNet.com

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Fine Needle Aspiration Biopsy of the Thyroid

Revising Medical Author: Ruchi Mathur, M.D.
Revising Medical Editor: William C. Shiel, Jr., MD, FACP, FACR

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. In fact, many are found incidentally during routine examinations or radiology testing. Thyroid nodules are also more common in women than in men. In fact, ultrasound studies have found that up to one in every three women has at least one thyroid nodule that may be too small to notice. (Usually, a nodule needs to be greater than one centimeter in diameter for it to be felt.). Interestingly, because women have so many more nodules than men, the incidence of detected cancer is higher in women then 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 (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 as an 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 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 it's 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.