Quick version
Ultrasound of the thyroid gland is a central part of the investigation of thyroid disease and is often used when a nodule, cyst or goiter is suspected. The examination provides detailed information about the size and tissue structure of the gland, can identify and assess the risk of nodules and often includes assessment of lymph nodes in the neck. With structured classification, such as EU-TIRADS, it is possible to determine when follow-up or fine needle aspiration is justified and at the same time avoid unnecessary investigation of low-risk findings.
A thyroid ultrasound is particularly valuable if you or a doctor has identified a lump in the neck, when the thyroid gland is felt to be enlarged, or when there is a clinical question about a cyst, nodule or goiter. Ultrasound complements blood tests and clinical examination and can often provide a clearer picture of what actually lies behind a palpation finding.
What can be seen during a thyroid ultrasound?
Ultrasound provides a good picture of the anatomy of the gland and the nature of the tissue. The examination is used to assess several central aspects that are crucial when investigating a lump, cyst or goiter.
The size and volume of the thyroid gland. Ultrasound is the most reliable method for measuring the volume of the thyroid and assessing whether the gland is enlarged goiter. This may be clinically relevant because large gland volume sometimes affects treatment strategy, for example when choosing between drug treatment, radioiodine or surgery.
The appearance of the parenchyma. The radiologist assesses whether the glandular tissue is smooth and homogeneous or whether it is more inhomogeneous/hypoechogenic, which can be seen in inflammatory or autoimmune conditions. Color Doppler can also be used to assess blood flow; for example, increased vascularity can be seen with increased disease activity, while decreased vascularity may occur in other phases or conditions.
Nodules and cysts. Ultrasound is very sensitive for identifying nodules in the thyroid gland and can often distinguish between solid nodules, cysts and mixed changes. Each nodule is assessed based on size, shape, demarcation, echogenicity, any microcalcifications and vascularity. This overall assessment then forms the basis for risk classification and whether fine needle aspiration may be appropriate.
Lymph nodes in the neck. The same examination often also assesses lymph nodes in nearby areas. The size, shape and preserved architecture are looked at, as well as whether the glands exhibit features that indicate reactivity or suspicion of malignant influence, which may be relevant in certain nodule findings.
Thyroid nodules as incidental findings (incidentaloma) – what does that mean?
Ultrasound can sometimes find a nodule in the thyroid gland that has not caused any symptoms and was not the actual reason for the examination. This is called incidentaloma (incidental finding) and is common, especially with increasing age.
Discovering an incidental finding is not in itself "bad"; on the contrary, ultrasound can sometimes identify changes that need to be followed up. At the same time, it is important to know that many thyroid nodules are benign and would never cause problems. If you search very broadly, you may end up in situations where small, low-risk findings lead to more checks, sampling or puncture investigations without changing the prognosis. This is usually described as overdiagnosis and can, however, create unnecessary concern.
Therefore, a clear indication and a structured risk assessment are important. When a nodule is found, it is assessed based on its ultrasound appearance and size, and if necessary, it is classified according to systems such as EU-TIRADS to determine whether follow-up or fine-needle aspiration is justified.
Assessment of nodules – EU-TIRADS
If a nodular change is identified, an initial risk assessment for malignancy is made based on the ultrasound characteristics and size of the nodule. The European Thyroid Association often recommends classification according to EU-TIRADS, where nodules are graded from low to high suspicion. The classification is then used to determine whether a nodule can be left without treatment, whether it should be followed over time or whether fine needle aspiration (FNAC) is indicated. A practical advantage of EU-TIRADS is that follow-up can in many cases be terminated completely if cytology shows a benign finding, which reduces the patient's follow-up burden.
Ultrasound in various thyroid diseases
Graves' thyrotoxicosis
In Graves' disease, ultrasound can be a valuable complement to clinical and blood tests. By assessing the appearance and vascularity of the parenchyma, one can get an idea of the disease activity and in some cases use this as support when monitoring and planning treatment with thyreostatics.
Subacute thyroiditis
In subacute thyroiditis, ultrasound can show inflammatory changes in the parenchyma and be used to monitor healing. It can be a support for adjusting treatment, for example how long anti-inflammatory treatment or corticosteroids need to be given.
Gestational thyrotoxicosis
Gestational thyrotoxicosis is usually self-limiting. Ultrasound can sometimes facilitate differentiation from Graves' disease, especially in situations where TRAK cannot be demonstrated or when the clinical picture is difficult to interpret.