Ultrasound of the Thyroid
This is a test that uses sound waves to take a picture of the thyroid. Similar to the prenatal ultrasound of the fetus, a cold lubricant jelly is placed on the neck; then, using an external probe, ultrasound images of the thyroid gland are obtained.
An ultrasound can reveal which thyroid nodules are larger than 1-1.5 centimeters, requiring further evaluation for cancer.
In addition to size, other nodule characteristics that can be noted on a thyroid ultrasound include the following:
- number of nodules,
- location of nodules,
- distinctness of borders,
- fluid versus solid contents,
- other nodule contents, such as calcium deposits, or
- the amount of blood flow (certain newer ultrasound machines can assess blood flow to the thyroid and its nodules).
Thyroid Nodules Overview
Nodules are simply lumps which are either solid or fluid-filled. The main function of the thyroid gland in the neck is to make thyroid hormone, which is essential for normal growth and metabolism.
Autopsy studies have revealed that up to 50% of all adults die carrying at least one thyroid nodule. These people may or may not have been aware of the presence of their thyroid nodules.
Thyroid nodules are found more commonly as people age.
Most of these thyroid nodules are benign (>80%) and not cancerous.
Only 10-15% of all thyroid nodules will be discovered to be thyroid cancer.
Finding cancer in a thyroid nodule is more likely in a person under the age of 30 or over the age of 60.
However, it is important to remember that only a small percentage of people with thyroid cancer die as a result of their thyroid cancer.
Fine Needle Aspiration Biopsy(FNAB)
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.
Related Thyroid Associations