Why Is a Thyroid Scan Needed for Multinodular Goiter?

If you have a multinodular goiter and blood tests show a low or suppressed Thyroid Stimulating Hormone (TSH), a thyroid scan is often used to find out if one or more of your nodules are producing too much thyroid hormone ^[1]. By mapping out which parts of your thyroid are highly active and which are not, the scan helps your doctor decide the safest next step for evaluating your nodules and managing your condition ^[2][3].

Why Low TSH Matters

TSH is a messenger hormone produced by the pituitary gland at the base of your brain. It tells your thyroid how much hormone to make. When your thyroid makes too much on its own, your body lowers the TSH level to try and slow the production down. A low TSH level suggests that your thyroid may be overactive, a condition called hyperthyroidism ^[4][1].

Your doctor will usually check other thyroid hormones (like free T4 and T3) and consider any symptoms you might have—such as a racing heartbeat, unexpected weight loss, tremors, or heat intolerance—to confirm if you have hyperthyroidism. In a multinodular goiter, this overactivity usually happens because certain nodules have started producing hormone independently, ignoring the body’s normal regulatory signals ^[4].

What the Scan Shows: Hot, Warm, and Cold Nodules

A thyroid scan (also known as radionuclide scintigraphy) gives your care team a map of how different parts of your thyroid are functioning ^[5]. You will swallow or be injected with a small, diagnostic dose of a radioactive tracer ^[6]. This involves a small radiation exposure that is much lower than the doses used for radioactive iodine treatments. The scan compares how much tracer each nodule absorbs relative to the surrounding thyroid tissue:

How Ultrasound and Scintigraphy Work Together

It is important to know that a functional thyroid scan does not replace a thyroid ultrasound ^[1]. An ultrasound takes a structural “picture” of all the nodules—showing their size, shape, and physical features ^[9][10].

While hot nodules have a very low risk of cancer, your doctor will still use the ultrasound to evaluate all your nodules (hot, warm, and cold). The ultrasound helps them determine if any nodule has suspicious structural features that require a fine-needle aspiration biopsy to evaluate for cancer ^[3][2]. The scan simply helps prioritize and inform that decision.

What to Expect and Next Steps

Waiting for imaging and biopsy decisions can be stressful. If your scan and blood work confirm that you have hyperthyroidism, your doctor will discuss your options. Antithyroid medications are often used to temporarily control hormone production and relieve symptoms. Definitive treatments to resolve the issue long-term, such as radioactive iodine therapy or surgery, may be recommended depending on the size of your goiter, your symptoms, and your overall health ^[6][2].

Things That Can Affect Your Scan

Certain factors can interfere with the scan or mean it isn’t safe for you to have one. Always tell your care team about:

• Recent imaging with iodine contrast: If you recently had a CT scan or angiogram with IV contrast, the extra iodine in your body can block the tracer from entering your thyroid. You may need to wait several weeks or months before a thyroid scan can give accurate results; your imaging center will determine the right timing based on their specific policies ^[11][6].
• Thyroid medications and supplements: Certain medications, like thyroid hormone pills, antithyroid drugs, and heart medications such as amiodarone, can change your scan results ^[12]. Dietary supplements containing kelp or high amounts of iodine can also interfere ^[6]. Do not stop your medications without explicit instructions from your doctor.
• Pregnancy: Tell your team if you are or might be pregnant. Diagnostic thyroid scans are generally avoided during pregnancy because the radioactive tracer can cross the placenta and potentially affect the developing baby’s thyroid ^[13][14]. An ultrasound is the preferred imaging choice if you are pregnant ^[15].
• Breastfeeding: Radiotracers can pass into breast milk ^[13]. Depending on the specific tracer used, you may need to pause breastfeeding and pump-and-dump for a certain period, or stop breastfeeding entirely for that infant. You must get written, tracer-specific instructions from the nuclear medicine department to keep your baby safe ^[13].