Ultrasounds are one of the most common imaging tests used to examine the thyroid gland.
A thyroid ultrasound uses high-frequency sound waves to create detailed images of the thyroid gland and surrounding tissues in real-time. This test is painless, non-invasive, and does not use radiation.
Why Doctors Order Thyroid Ultrasounds
Doctors may order a thyroid ultrasound for several reasons, including:
- To evaluate thyroid nodules found during a routine physical exam or other imaging test to determine if they are fluid-filled cysts or solid masses and if they appear benign or suspicious.
- To get more information about an abnormal thyroid that was found during a CT scan or neck MRI done for another reason.
- To further evaluate abnormal results from thyroid blood tests, such as high or low thyroid hormone levels (TSH, T3 and T4).
- To check the size and characteristics of thyroid nodules already diagnosed to see if they have grown or changed over time, which may indicate a higher risk of thyroid cancer.
- To determine if thyroid gland swelling is due to thyroiditis (thyroid inflammation) or Graves’ disease (overactive thyroid).
- To check parathyroid glands that may be enlarged or abnormal.
- To examine lymph nodes near the thyroid for swelling or abnormalities that might indicate the spread of thyroid cancer.
- To check for suspected neck masses, fluid around the thyroid, or abnormalities seen during other imaging exams like CT or MRI.
- To visualize thyroid cancer and the spread of thyroid cancer to nearby tissue, lymph nodes or distant sites.
- To perform ultrasound-guided fine needle aspiration (FNA) biopsy of the thyroid.
So in summary, thyroid ultrasounds allow doctors to evaluate thyroid nodules, inflammation, cysts and tumors in detail; determine if further testing or procedures are needed; guide biopsy needles to collect thyroid cells for analysis; and monitor existing thyroid conditions over time.
How Thyroid Ultrasounds Work
Thyroid ultrasounds use high-frequency sound waves to create detailed black-and-white images of the thyroid gland and surrounding tissues in real time. This allows evaluation of the structure and texture of the thyroid parenchyma itself, as well as visualization of blood flow patterns to the gland.
During the examination, a technician will apply a warm, water-based gel to your skin over the neck area and will then press a small hand-held device called a transducer to your skin and slide it back and forth over the area of interest.
The transducer emits inaudible sound waves that penetrate into nearby tissues, bounce off internal structures, and return echoes back to the probe. These echoes are converted into images that appear on a computer screen for the technician and reporting radiologist to evaluate.
Thyroid ultrasound images show exquisite detail down to the millimeter level. Radiologists can clearly visualize thyroid nodules, lesions, inflammation, fluid collections, nearby lymph nodes, surrounding blood vessels and more in multiple planes. The structure, size, shape, exact location, texture and blood flow to any thyroid abnormalities can be analyzed.
Comparison ultrasound views are also obtained routinely on the opposite side for reference. A full series of images are captured in loops from multiple angles and orientations that can be re-examined by the radiologist when writing up the final report.
What to Expect During the Exam
Thyroid ultrasounds are quick, easy exams that take only 15 to 30 minutes from start to finish in most cases. When you arrive for your thyroid ultrasound, the technician will ask you questions about your medical history, symptoms and any prior imaging tests you’ve had.
You will be asked to lie down on your back on the exam table and extend your neck with your shoulders flat to optimize visualization. Usually, no specific preparation is required beforehand.
The technician will apply a generous amount of warm, clear ultrasound gel to your upper chest and lower neck. This gel allows smooth back-and-forth gliding of the transducer across your skin without pressing too hard. You may feel some pressure as the ultrasound probe is firmly pressed and rocked to scan different areas.
As the technician scans cross-sectional slices through your thyroid gland from multiple directions, real-time images will appear on a monitor. The technician will likely take some frozen images and video clips to document the size, structure and blood flow through any nodules or masses seen. Comparison images of the opposite thyroid lobe may also be captured.
Once a full set of ultrasound images are acquired, the radiologist will analyze them on a medical-grade monitor and issue a detailed report summarizing the findings. This report will go directly to your doctor who ordered the thyroid ultrasound so they can discuss the results with you and recommend any needed follow-up.
What Does a Normal Thyroid Gland Look Like on an Ultrasound?
When the doctor examines your thyroid on an ultrasound, they look for a butterfly-shaped gland in your neck. The thyroid has two halves, called lobes, that are connected by a tiny bridge of tissue named the isthmus.
Here is what the doctor checks on the ultrasound:
- Size – The thyroid is typically around 4 to 6 centimeters (1.5 to 2.5 inches) long in adults. If your thyroid looks a lot bigger, you may have a condition called a goiter.
- Shape – A healthy thyroid gland has a smooth, normal shape. If your thyroid looks lumpy or oddly shaped, it could mean you have nodules or cysts.
- Texture – The texture of a normal thyroid looks smooth and consistent. If there are areas on the ultrasound that seem darker or brighter than the rest of your thyroid, it might signal an abnormal growth.
- Blood Flow – The doctor may also examine the blood vessels around your thyroid using a special ultrasound called Doppler. Too much or too little blood flowing in the gland could mean thyroid issues.
What Does an Unhealthy Thyroid Gland Look Like?
In some cases, the ultrasound highlights problems with the thyroid:
Thyroid Nodules
Nodules are lumps or growths on the thyroid. Most thyroid nodules are harmless, but some can be cancerous. On the ultrasound, a nodule may look like a darker or brighter spot compared to the rest of the gland.
- Doctors check the size of the nodules and whether they are solid or filled with fluid. Fluid-filled nodules are called cysts.
- Cysts are usually not harmful, but solid nodules may need more testing.
Enlarged Thyroid Gland (Goiter)
If your thyroid looks a lot bigger than normal, you may have a goiter. This can happen if your thyroid is overactive, underactive, or lacking iodine in your diet.
On the ultrasound, a goiter appears as an enlarged thyroid. The doctor may also spot nodules or cysts related to the goiter.
Signs of Thyroid Cancer
Rarely, an ultrasound detects signs of thyroid cancer. Cancerous nodules often have distinct traits compared to benign nodules.
- Irregular borders or shapes
- Tiny calcium deposits called microcalcifications
- Increased blood flow on a Doppler ultrasound
If the doctor sees a suspicious nodule, they may recommend a biopsy to test if it is cancerous.
Role of Ultrasound in Thyroid Biopsies
If a thyroid nodule is considered intermediate or high risk after ultrasound evaluation, a fine needle aspiration (FNA) biopsy is usually recommended. This minimally invasive biopsy procedure uses a very thin needle to extract cells from different areas of a nodule for examination under the microscope by a pathologist.
Thyroid ultrasound plays a key role in guiding proper needle placement for accurate biopsy samples. This technique is called ultrasound-guided FNA biopsy and it continues to grow in popularity.
Real-time ultrasound allows the radiologist to choose a safe needle path avoiding critical structures like blood vessels or nerves. It also ensures the most abnormal-appearing sections of a heterogeneous mass are directly targeted under direct visualization. Ultrasound confirms the tip of the needle is correctly positioned within the nodule itself throughout sample collection.
Multiple biopsy specimens can be obtained from different areas of large or complex nodules in a single session with ultrasound guidance. This further enhances diagnostic accuracy.
Limitations of Thyroid Ultrasound Imaging
While a thyroid ultrasound is extremely helpful for anatomical evaluation of the thyroid gland, it does have some limitations:
- Ultrasound has limited accuracy in predicting if thyroid nodules are malignant or benign based on imaging characteristics alone. There is an overlap in how benign adenomas and cancerous nodules may appear. A definitive diagnosis requires a biopsy.
- Deeply located or posterior thyroid nodules can be difficult to fully visualize and characterize depending on body habitus and equipment limitations. Image quality degradation or obscured views may occur when imaging through dense tissue, bone or air.
- Ultrasound cannot reliably detect diffuse thyroiditis, Graves’ disease and hormonal thyroid changes in all cases. Some hyperfunctional conditions have very subtle or misleading sonographic findings despite symptoms or lab abnormalities.
- Detection of smaller metastatic lymph nodes and tiny metastatic thyroid cancer deposits in other organs falls below the resolution limits of ultrasound technology. This can underestimate the cancer stage in some cases until the disease becomes more extensive.
- Results are operator-dependent, requiring an experienced ultrasonographer for image acquisition paired with specialized expertise in thyroid interpretation. Diagnostic accuracy varies based on the skill, technique and thoroughness of whoever is scanning or reading the study. Poorly performed ultrasounds may miss key findings.
For these reasons, ultrasound results should always be correlated with clinical history, physical exam findings and thyroid function blood tests when making the diagnosis and devising treatment plans for thyroid disease. However, despite some shortcomings, most thyroid specialists still consider ultrasound the single best imaging modality for dedicated evaluation of thyroid gland anatomy and characterization of nodules.
Who Should Have a Thyroid Ultrasound?
Many thyroid experts agree that all new thyroid nodules found on physical examination should be evaluated by ultrasound, regardless of size. This is because sudden thyroid gland enlargement or palpable abnormalities might indicate thyroiditis, thyroid cancer or other pathology potentially requiring treatment.
Thyroid ultrasounds may also be ordered for goiter, suspected inflammation or infection, unexplained neck mass or fluid, hoarse voice suggesting vocal cord paralysis or immense thyroid growth impacting breathing.
Also, abnormal thyroid lab test results usually prompt ultrasound referral as the next logical step to identify anatomic correlates that may require biopsy or surgery if malignant. And ultrasound screening tends to be recommended for certain high-risk groups like patients with a family history of thyroid cancer or prior head/neck radiation exposure.
In summary, if a physical examination reveals a suspicious thyroid mass or focal nodule not previously imaged, ultrasound is warranted for further inspection of its size, characteristics and growth potential.
Conclusion
Thyroid ultrasound serves as an accessible, safe initial test for more definitive characterization when thyroid disease is suspected either because of visible or palpable neck abnormalities on routine wellness checks or due to patient-reported symptoms, combined with corroborating lab values or clinical signs.