Fine-needle aspiration biopsy of the thyroid nodule is a procedure in which a small sample of cells is obtained from a thyroid nodule with the aid of a thin needle under ultrasound guidance. Thereafter the cells are visualized under a microscope to help diagnose cancer, infection, or other thyroid problems.
It is a safe and simple procedure usually done at a doctor’s office. During the test, you will lie on your back with a pillow under your shoulders, your head tipped backward, and your neck extended. This position pushes the thyroid gland forward, making it easier to do the biopsy. During the procedure, you may feel some neck pressure from the ultrasound probe and from the needle. You will be advised to remain as still as possible and avoid coughing, talking and swallowing during the biopsy.
There is very little you need to do to prepare for thyroid FNA. Ask your healthcare provider if you need to stop ta king any medicines before the procedure like blood thinners. You should be able to eat and drink normally before the procedure.
The neck is first be cleaned with an antiseptic. A local or topical anesthetic may be applied next. For the biopsy, your doctor will use a very thin needle to withdraw cells from the thyroid nodule. The needle used is smaller in diameter than those used in most blood draws. Your doctor will insert the needle through the skin and into the thyroid nodule. After the sampling, which only takes several seconds, the needle will be removed. New needles are used for additional samples. Several samples of cells will be obtained, by sticking a fine needle in various parts of the nodule usually between two and six times . This assures a better chance to find cancerous cells if they are present. If there is fluid in the nodule, a syringe may be used to drain it.
Once the biopsy is completed, pressure will be applied to the neck. A small bandage will be applied over the area where the needle was inserted. The procedure usually lasts less than 30 minutes.
After the procedure, you may be asked to sit up slowly to prevent you from getting lightheaded. Most patients typically leave feeling well. There are very few, if any, restrictions on what you can do after a thyroid biopsy. Because of this, it is not generally necessary to bring a companion to help or drive you home. Some neck discomfort at the site of the biopsy is expected following the procedure. Nonprescription pain medicine like Tylenol and ice compresses can be used to relieve discomfort.
The biopsy samples may be used to make slides immediately and/or collected in a solution to wash excess blood. Specially trained doctors called cyto-pathologists, then make slides from the material and examine them under a microscope to make a diagnosis.
Generally, results return the same day. Sometime can take up to 1-2 days.
Results of the thyroid biopsy are given as one of six possible diagnoses, according to the Bethesda System for Reporting Thyroid Cytopathology. Please note that the percentages below may be somewhat different at different institutions and centers.
Benign – This accounts for up to 70% of biopsies when using the Bethesda System (one of the most common ways that cyto-pathologists classify nodule biopsy specimens). The risk of malignancy in this group is typically less than 3%. These nodules are generally monitored with a follow up ultrasound within 12-18 months and if needed, periodically after that.
Malignant (cancer) – This account for 3-7% of all biopsy specimens. The most common type of thyroid cancer seen in these biopsies is papillary thyroid cancer. When a biopsy comes back as malignant, there is a 97- 99% chance that it is truly a cancerous lesion. Almost all of these nodules will go to surgery (thyroidectomy).
Suspicious for malignancy – When a biopsy result returns as suspicious for malignancy, there is a 60-75% chance of cancer. The cyto-pathologist will see features that are worrisome, but not diagnostic of cancer. The treatment is typically surgery.
Atypia of Undetermined Significance (AUS) or Follicular Lesion of Undetermined Significance (FLUS) – This category alternatively is called “indeterminate.” These specimens have some features that are worrisome and some features that look more benign. This diagnosis carries a 5-15% risk of malignancy, although there is some variability among institutions. A repeat biopsy and/or genetic testing may be useful in these cases.
Follicular Neoplasm or ‘Suspicious for follicular neoplasm’ – This category alternatively may be called “indeterminate” as well. This category carries a 15-30% risk of malignancy. It is difficult to tell if these nodules are benign or malignant unless taken out. Genetic testing may be useful in these cases. When needed, surgery removing half of the thyroid (the side with the nodule) is performed for diagnosis and treatment.
Non-diagnostic – This means that there are not enough cells in the sample to make a diagnosis. Despite our best efforts and even when we can see that the needle was in the nodule during the biopsy, the specimen sometimes does not have enough thyroid follicular cells to make a proper diagnosis. Non-diagnostic samples can also occur when only cyst fluid is taken out, and for other reasons, such as the presence of too much blood. In these cases, the biopsy should be repeated, and if non-diagnostic a second time, consideration is given to a third biopsy, monitoring, or surgery.
Within the past few years, several molecular tests have become available to help determine whether some nodules are cancerous or benign. These tests look at many genes within the thyroid nodule’s genetic information. They are used when a nodule biopsy comes back with a diagnosis of ‘indeterminate’. Sometimes, the person doing the biopsy will perform an additional pass of the needle to obtain material for such a test. The extra pass is usually done at the time of the first biopsy or could be done during repeat biopsy.