What is a thyroid ultrasound?

An ultrasound is an imaging study that makes use of echoes from sound waves to generate pictures of a part of the body. When sound waves produced at fixed frequencies are directed towards a specific part of the body, they are reflected back in patterns that vary depending on the size, shape, and density of the structures that are encountered. A sensor can be used to decode the patterns of reflected sound waves in order to create images. Ultrasounds are commonly used to examine fetuses during pregnancy and to analyze the motion and flow of blood in the heart. Ultrasound can also be used to image nodules in the thyroid gland.

What information can it provide?

A thyroid ultrasound can provide accurate information about the structure of the thyroid gland. Pictures obtained by directing sound waves at different angles can measure the size of the lobes of the thyroid gland. Thyroid nodules can located, measured, and examined to determine if they are solid or cysts filled with fluid. The shape and contour of each lobe can be outlined to see if it extends downward into the chest or towards the swallowing tube (esophagus) or windpipe (trachea). If an ultrasound study is expanded to fully examine other parts of the neck (referred to as a cervical or neck ultrasound), it can check to see whether there are enlarged lymph nodes in various regions of the neck. While a thyroid ultrasound provides detailed structural information, it does not provide direct information about gland function. It can tell if the thyroid gland is enlarged, but can't tell whether the enlargement is due to overactivity or underactivity. Ultrasound cannot reliably distinguish between benign (not cancerous) and malignant (cancerous) thyroid nodules. However, certain features of a nodule, such as being a small simple cyst, may increase the chance of it being benign, whereas other findings, such as extension beyond the capsule around the thyroid gland, suggest malignancy.

How is it done?

Thyroid ultrasound studies can be performed by endocrinologists, radiologists, or by technicians who capture images that are later interpreted. The patient usually lies back on a stretcher or table with a pillow placed under the head or neck. A gown or towel may be placed over the chest. When the patient is comfortable, a thin layer of a clear watery gel is applied to the front of the neck. This helps to increase the transmission of sound waves through the skin. An instrument called a probe is placed perpendicular to the lower front part of the neck. The probe is used to generate sound waves and to sense the reflections of sound waves created by interactions with tissues in the body. These sound waves cannot be heard or felt at all by the patient. The probe is attached to a long cable that leads to a console that houses a video screen with controls to adjust the picture. As gentle pressure is applied, the probe is moved across the lower front part of the neck and directed at different angles to examine both lobes of the thyroid gland. At certain points it may be held firmly in place while a snapshot of an image is taken. Measurements are usually taken from these snapshots, which may be printed out for review. When the study is completed, the gel is wiped off.

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