FINE NEEDLE ASPIRATION BIOPSY (FNAB)
A biopsy is the only way to tell if a thyroid nodule is cancerous. But cancer may be more likely if you have:
- A single, hard lump that feels very different from the rest of the thyroid tissue or other thyroid nodules.
- A nodule that keeps growing for weeks or months.
- A nodule that does not move when you touch it.
- Swollen lymph nodes in your neck.
- A hoarse or scratchy voice that does not go away.
Some other conditions that cause similar symptoms include hyperthyroidism and thyroiditis.
- If a thyroid nodule is larger than 1 cm, or it has other worrisome characteristics seen on ultrasound or other imaging tests, then a FNAB may be performed.
- This office procedure does not require anesthesia and consists of passing small needles (similar to those used to draw blood from the arm) into the thyroid nodule in the neck. This is a quick and usually painless procedure.
- This procedure may be done on multiple nodules.
- Ultrasound guidance may be used to assist in the FNAB of nodules that are bigger than 1-1.5 cm but cannot be felt on physical examination.
- A sample of the contents of each nodule (to include fluid, blood, or tissue) are removed in the needle and examined by the pathologist under a microscope.
- Pathologists can identify certain features in the nodule sample.
FNAB results are characterized as one of the following:
- Benign: This is the most common outcome of a FNAB. The typical finding is a nodule filled with colloid protein, a normal component of the thyroid. Benign nodules can be followed over time with serial physical exams or ultrasound exams. Further intervention is only necessary if enlargement occurs or new symptoms develop.
- Malignant: Some thyroid cancers can be diagnosed directly from the FNAB results (for example, papillary thyroid cancer). Other thyroid cancers cannot be diagnosed from the FNAB results (such as follicular thyroid cancer) because the diagnosis rests not simply upon the appearance of the tissue within the nodule, but also on the level of the invasion of surround blood vessels and tissue by the nodule. For these nodules, surgical removal of a portion or the entire thyroid is recommended.
- Indeterminate: This is neither definitively benign nor malignant. Given that the risk for cancer is increased by 20% in such cases, surgical removal of a portion or the entire thyroid is typically recommended. Often, a radionuclide scan will be done to obtain functional information (if the nodule is actively producing thyroid hormones) in order to avoid an unnecessary surgery.
- Non-diagnostic: This means that there are not enough of the tissue cells present in the sample to make a diagnosis. Non-diagnostic FNABs will typically result in a repeat FNAB or definitive surgery.
Cystic nodules more often result in a non-diagnostic FNAB due to higher fluid content than solid content in the sample obtained from the nodule.