Nodules - Tests & Scans
Written by Monique Atkinson and endorsed by Dr Hieu Nguyen
A nodule in the thyroid gland can be a solid lump, a cyst or a complex growth. In a multinodular goitre, the enlarged thyroid contains multiple nodules. Thyroid nodules are very common and occur more frequently in older people. Most of these nodules are small and only obvious on ultrasound examination. Fifty per cent of normal functioning thyroid glands contain nodules which can be detected in autopsy studies. According to the Medical Journal of Australia about 5 % to 15 % of nodules are cancerous.
The following thyroid imaging tests can be useful in the diagnosis and treatment of nodules.
Investigation of Thyroid Nodule
Nuclear Thyroid Scan – ‘Functional Scan’
When you receive a nuclear thyroid scan (also called radioactive iodine uptake test) then you are first given radioactive iodine (131) or radioactive pertechnetate usually by injection. The nuclear medicine then travels to the thyroid gland and the radiation is detected by a gamma camera and the image of your thyroid gland can be seen on a computer screen. If the nodule takes up the iodine then it is a ‘hot’ nodule (functioning) and if the nodule does not take up iodine then it is not active and it will appear as ‘cold’ on the screen.
This test is only useful if your thyroid function test shows endogenous “over-activity”. This is not a test to see whether the nodule is cancerous or not.
Ultrasound – “Topographic Scan”
The ultrasound will be able to determine the size of the nodule and its structure (whether it is solid or a cyst (fluid filled) or mixed).
If the ultrasound shows the following features, then further investigation with FNA (fine needle aspiration) is warranted;
- Irregular border
- Increased vascularity
Fine Needle Aspiration Biopsy
If you have a nodule and your doctor wants to rule out cancer, then he will order a FNAB (fine needle aspiration biopsy). A fine needle is inserted into the nodule to obtain cells which are then sent off to a laboratory for examination. A diagnosis of a cancer can be made based on the characteristics of the cells. This is the best test currently available for the diagnosis of thyroid cancer and a FNAB can be done with the help of an ultrasound machine. This method is about 90 % accurate.
The majority of thyroid cancer cells (from papillary cancer, medullary cancer & anaplastic thyroid cancer) can be diagnosed with a FNAB. However, in follicular thyroid cancer, the microscopic examination of a FNAB cannot differentiate between benign and cancerous cells. In this situation, the only way to decide definitely is by surgery where the whole nodule is removed and fully examined for capsular invasion and/or vascular invasion (WHO’s criteria for follicular thyroid cancer).
Therefore if you have had a FNAB and you were told that the nodule was benign; that nodule has only 1% chance of being cancerous. If the result of the FNAB shows atypical cell changes, than the risk of the nodule being cancerous is up to 25 %.
There is some controversy about the minimum size of a nodule that should be investigated. Some specialists recommend a biopsy of a nodule when it is over 1 cm and other specialists believe the nodule should be bigger than 1.5 cm. However nodules which are smaller than 1 cm can be cancerous too and every patient is different. If the nodule is very small (less than 1 cm) than the following factors also need to be taken into consideration;
- You are at an increased risk of developing thyroid cancer if you have a history of head or neck irradiation you received for the treatment of enlarged tonsils, adenoids or various skin conditions such as acne.
- Family history of thyroid cancer (usually two immediate family members).
- History of external radiation to the neck for the treatment of cancer.
- Exposure to radioactive material from nuclear accidents.
It is important to note that a FNAB of a small lesion can technically be a challenge when the sample provided is inadequate.
In medullary thyroid cancer, the calcitonin level is abnormally high.