The thyroid gland is a small, butterfly-shaped structure positioned low in the front of the neck. Its primary function is to produce hormones that regulate the body’s metabolism, affecting processes like heart rate, body temperature, and energy use. A thyroid ultrasound is a safe, non-invasive imaging procedure that uses high-frequency sound waves. These sound waves bounce off internal structures and are converted into images on a monitor, providing a detailed look at the gland’s anatomy without using ionizing radiation.
Why Is a Thyroid Ultrasound Performed?
Doctors frequently order a thyroid ultrasound to investigate structural abnormalities found during a physical examination. The most common indication is the presence of a palpable lump or mass, known as a thyroid nodule. The imaging is also used to evaluate an overall enlargement of the gland, a condition called goiter.
The scan is also used for monitoring known thyroid conditions, such as tracking changes in pre-existing nodules over time. Although ultrasound cannot measure hormone levels, it is often performed when blood tests show abnormal thyroid function, like hyper- or hypothyroidism, to determine if a structural problem is the underlying cause. It also serves as a screening tool for patients at higher risk of thyroid cancer due to family history or prior neck radiation exposure.
The Examination Process
Preparation for a thyroid ultrasound is minimal, requiring no changes to diet or medication schedules. Patients must remove any neck jewelry and lie on their back on an examination table. A pillow is placed beneath the shoulders to gently extend the neck, making the thyroid region accessible for scanning.
A clear, water-based gel is applied to the skin to eliminate air pockets, ensuring sound waves from the transducer pass effectively into the body. The sonographer presses a small, hand-held device called a transducer against the skin and moves it across the area to capture images. The procedure is painless, though patients may feel pressure, and typically lasts between 15 to 30 minutes.
Key Findings Revealed by the Scan
The ultrasound provides a precise picture of the thyroid’s physical state, characterizing its overall size and internal texture. The scan determines if the gland is uniformly enlarged (goiter) or if its texture is heterogeneous, which often suggests an inflammatory process like thyroiditis. Doppler technology during the scan can also assess blood flow within the gland, which can indicate inflammation associated with conditions such as Graves’ disease.
The most common findings are thyroid nodules, which appear as discrete masses distinct from the surrounding tissue. These nodules are categorized by their composition, distinguishing between fluid-filled cysts, solid masses, or mixed solid and cystic lesions. The scan then focuses on features that help estimate the likelihood of malignancy, since most nodules are benign.
Suspicious features are carefully assessed:
- Microcalcifications, which appear as tiny bright spots and are strongly associated with papillary thyroid cancer.
- A shape that is “taller-than-wide” on the image, considered a specific sign of concern.
- Nodules with irregular, spiculated, or microlobulated margins, which are more likely to be malignant than those with smooth, well-defined borders.
- Enlarged or abnormal-looking lymph nodes in the neck, which can be an indicator of potential cancer spread.
Understanding the Results and Next Steps
The detailed features observed on the ultrasound are used to stratify the risk of malignancy, a process often standardized by systems like the American College of Radiology (ACR) Thyroid Imaging Reporting and Data System (TI-RADS). This system assigns points to suspicious characteristics to categorize nodules into a risk level, which then guides the next steps. A nodule with features suggesting a low risk may only require regular ultrasound surveillance, with follow-up scans scheduled at intervals of one year or more.
For nodules that meet specific size thresholds within the higher-risk TI-RADS categories, a Fine Needle Aspiration (FNA) biopsy is recommended. This procedure uses the ultrasound image to precisely guide a thin needle into the nodule to collect a small sample of cells for microscopic examination. The goal is to avoid unnecessary biopsies for the vast majority of benign nodules while ensuring that suspicious lesions are thoroughly investigated. The results of the ultrasound, combined with any biopsy findings, provide the necessary information for the physician to create an appropriate long-term management plan.