Thyroid ultrasound is an imaging method used to assess the structure of the thyroid gland. This examination helps to detect nodules, cysts or other abnormalities in the thyroid gland.1,2
What is a thyroid ultrasound, and how is it done?
Ultrasound uses sound waves to produce pictures of the thyroid gland and the neighbouring structures in the neck. Thyroid ultrasound uses no radiation.3
No special preparation is needed: on the day of the examination you can eat, drink and take your usual medicines. The examination follows these steps:2
- You lie on your back on the examination couch.
- A water-based gel is put on the skin of your neck.
- A hand-held probe is pressed onto the gel; it may be moved to a few places around the thyroid to take pictures from different angles.
- When the pictures are complete, the gel is wiped off.
The gel may feel cold and the probe may be slightly uncomfortable, but the examination should not hurt. A thyroid ultrasound usually takes around 30 minutes from start to finish.2,3
What does it show, and what does it not show?
Ultrasound shows whether the thyroid gland is larger than usual and whether there is a growth or any other change in or around it. Thyroid nodules are frequently detected by ultrasound; nodules too small to be felt can be seen as well. Ultrasound helps to distinguish fluid-filled cysts from solid lesions. The distinction matters: the risk of cancer is higher in completely solid nodules than in mainly cystic ones. When a thyroid nodule is suspected, the lymph nodes in the middle and at the sides of the neck are assessed as well.1,2,4
Ultrasound cannot show how the gland is working, that is, whether it is underactive, overactive or normal; that is measured with blood tests. Nor can it diagnose cancer on its own: some features strongly suggest that a nodule is benign and others raise concern, and in some cases benign and malignant nodules cannot be told apart on the picture with complete certainty.2,3,4
How are nodules described, and when is a needle sample taken?
The size, shape and internal structure of nodules provide information about the risk of cancer. The report records the size, position and ultrasound features of a nodule and places it in a risk category; the system preferred in Europe is called EU-TIRADS. The categories run from 2 (benign) through 3 (low risk) and 4 (intermediate risk) to 5 (high risk). A nodule with at least one of the following features falls into the high-risk category:1,4
- Irregular shape
- Irregular margins
- Microcalcifications (very small calcifications)
- Marked hypoechogenicity (the nodule looks very dark on the picture)
You may come across these terms in your ultrasound report.4
Whether a fine-needle sample is advised depends on the risk category and the size of the nodule: the size thresholds in the guideline are over 10 mm for category 5, over 15 mm for category 4 and over 20 mm for category 3. Examination findings and blood tests are taken into account as well, and the decision is made together with the patient. The sample is taken under ultrasound guidance with a very thin needle (a local anaesthetic may not even be needed), and the cells are examined under a microscope.1,4
Thyroid ultrasound in pregnancy
Thyroid ultrasound can also be used in pregnancy when imaging is needed. No risk from ultrasound has been shown in pregnancy, and together with magnetic resonance imaging it is the imaging technique of choice for a pregnant patient. Like any test, it is done when it is expected to answer a clinical question.5
After the ultrasound
The pictures are assessed and reported; your doctor interprets the ultrasound results and shares them with you. This interpretation matters for an accurate diagnosis and the right course of treatment. An abnormal result does not automatically mean a serious problem; it means that something needs to be checked.2,3
The next step depends on the findings: nothing further, a repeat ultrasound, a blood test or a needle sample. Ultrasound is used to see whether a thyroid nodule has grown over time. For nodules that are not sampled, the guideline sets the timing of the next check by risk category and size: from no further evaluation for small nodules in the benign and low-risk categories to re-evaluation every six to twelve months in the high-risk category.3,4
Thyroid ultrasound is therefore central to assessing the thyroid, and it helps both patients and doctors to understand the condition of the gland.4
References
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American Thyroid Association. Thyroid nodules [Internet]. Alexandria (VA): American Thyroid Association; [cited 2026 Oct 5]. Available from: thyroid.org ↩
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Cleveland Clinic. Thyroid ultrasound [Internet]. Cleveland (OH): Cleveland Clinic; [updated 2025 May 6; cited 2026 Oct 13]. Available from: my.clevelandclinic.org ↩
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RadiologyInfo.org. Thyroid ultrasound [Internet]. Oak Brook (IL): Radiological Society of North America; [reviewed 2023 May 1; cited 2026 Oct 12]. Available from: radiologyinfo.org ↩
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Durante C, Hegedüs L, Czarniecka A, Paschke R, Russ G, Schmitt F, et al. 2023 European Thyroid Association clinical practice guidelines for thyroid nodule management. Eur Thyroid J. 2023;12(5):e230067. doi:10.1530/ETJ-23-0067 ↩
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American College of Obstetricians and Gynecologists, Committee on Obstetric Practice. Committee Opinion No. 723: guidelines for diagnostic imaging during pregnancy and lactation. Obstet Gynecol. 2017;130(4):e210-e216. doi:10.1097/AOG.0000000000002355 ↩