Introduction: Who Should Undergo Diagnostics and When

Thyroid nodules are lumps or growths that develop within the thyroid gland, which sits at the base of your neck just below your Adam’s apple. These nodules are remarkably widespread throughout the population. Research shows that healthcare providers can feel thyroid nodules during physical examination in approximately 5% to 7% of adults, but when ultrasound imaging is used, nodules are detected in 20% to 76% of adults.^[1] Some studies suggest that up to 50% of people develop thyroid nodules by age 60, with over 90% being benign.^[23]

Most thyroid nodules don’t cause any symptoms at all. Often, they are discovered completely by accident during routine physical examinations or imaging tests done for entirely different reasons, such as CT scans or ultrasounds of the neck area.^[7] Sometimes patients discover nodules themselves by noticing a lump in their neck while looking in a mirror, buttoning a collar, or fastening a necklace.^[7] You should seek medical evaluation if you notice any swelling or lump in your neck, especially if it affects your breathing or swallowing.^[2]

While the vast majority of thyroid nodules are benign, a small proportion—approximately 4% to 6.5%—do contain thyroid cancer.^[1] This is why proper evaluation is essential. Even though most nodules turn out to be harmless, ruling out cancer early ensures the best possible outcomes if treatment is needed. Women are affected about four times more often than men, and the likelihood of having thyroid nodules increases with age.^[1]

Certain factors increase the risk of having thyroid nodules. Living in areas where food isn’t fortified with iodine makes nodules more common, as iodine is necessary for the thyroid gland to make hormones.^[1] Other risk factors include a history of radiation to the head, neck, or chest, a family history of thyroid nodules or thyroid cancer, increasing age, iron-deficiency anemia, smoking, obesity, metabolic syndrome, alcohol consumption, and increased levels of certain hormones.^[1]

Classic Diagnostic Methods for Thyroid Nodules

When a thyroid nodule is suspected or discovered, doctors follow a systematic approach to determine whether it is benign or requires further attention. The diagnostic process involves several steps, each providing important information about the nodule’s characteristics and potential risk.

Physical Examination

The first step in diagnosing a thyroid nodule is a physical examination of the neck area. Your doctor will carefully feel your neck to check for lumps, assess their size and texture, and examine the surrounding lymph nodes. This simple examination can reveal whether a nodule is present and provide initial clues about its nature.^[5] During this exam, your doctor will also ask about any symptoms you may be experiencing, such as difficulty swallowing, breathing problems, voice changes, or pain in the neck area.

Blood Tests for Thyroid Function

After a nodule is detected, measuring thyroid-stimulating hormone (TSH) levels in the blood is an essential next step. TSH is a hormone produced by the pituitary gland that tells your thyroid how much thyroid hormone to make. This test helps determine if your thyroid is functioning normally.^[10] Most thyroid nodules occur in people with normal thyroid function, meaning their TSH levels are within the normal range.^[7]

Your doctor may also measure levels of thyroxine (T4) and triiodothyronine (T3), the actual thyroid hormones that regulate metabolism, body temperature, heart rate, and other vital functions.^[1] These tests help identify whether the nodule is producing too much or too little thyroid hormone. If TSH levels are low, it suggests the nodule may be producing excess thyroid hormone on its own, a condition called hyperthyroidism.^[10]

Thyroid Ultrasound

Ultrasound is one of the most important tools for evaluating thyroid nodules. This test uses sound waves to create detailed images of the thyroid gland and can show the size, shape, structure, and location of nodules.^[10] Ultrasound can determine whether a nodule is solid, filled with fluid (called a cyst), or a combination of both. It can also reveal specific features that help doctors assess the likelihood of cancer.

Healthcare providers should perform thyroid ultrasound with a survey of the cervical lymph nodes (the lymph nodes in the neck) in all patients with thyroid nodules.^[14] This comprehensive examination helps identify any suspicious spread beyond the thyroid itself. Certain ultrasound characteristics raise concern for malignancy, including solid composition, low echogenicity (appearing darker on the image), irregular borders, and tiny calcium deposits called microcalcifications.^[14]

Radionuclide Thyroid Scan

If blood tests show that TSH levels are low, indicating the thyroid may be producing too much hormone, a radionuclide thyroid scan (also called a thyroid uptake scan) should be performed.^[10] During this test, a small amount of radioactive iodine is given, usually through a vein in your arm. You then lie on a table while a special camera creates an image of your thyroid on a computer screen, showing how the thyroid tissue takes up the radioactive material.

Nodules that produce excess thyroid hormone, called hot nodules, take up more radioactive iodine than normal thyroid tissue and show up brightly on the scan. Hot nodules are rarely cancerous and typically do not require tissue sampling.^[10] Conversely, nodules that take up less iodine are called cold nodules. While cold nodules can be benign, they have a higher likelihood of being cancerous and usually require further evaluation with a biopsy. However, the thyroid scan alone cannot definitively tell which cold nodules are cancerous and which are not.^[10]

Fine-Needle Aspiration Biopsy

Fine-needle aspiration (FNA) biopsy is the most accurate and cost-effective method for evaluating whether a thyroid nodule contains cancer cells. During this procedure, a very thin needle is inserted into the nodule to remove a small sample of cells for examination under a microscope.^[5] Ultrasound guidance is typically used to ensure the needle is placed precisely in the correct location within the nodule.^[10]

The procedure is usually performed in a doctor’s office and takes about 20 minutes, similar to having blood drawn.^[17] There are few risks, and patients can typically return to their normal activities immediately afterward. Fine-needle aspiration is recommended for thyroid nodules that are 1 centimeter or larger and have suspicious features on ultrasound.^[14] Nodules with suspicious characteristics and solid nodules that appear darker than surrounding tissue (hypoechoic) and measure 1 cm or larger require aspiration.^[14]

The cell samples obtained from the biopsy are classified using a standardized system called the Bethesda System, which has six categories ranging from category 1 (nondiagnostic or unsatisfactory sample) to category 6 (malignant, meaning cancer is confirmed).^[14] Categories 3 and 4 are considered “indeterminate,” meaning the cells look unusual but it’s unclear whether they are benign or cancerous. In these cases, additional testing or surgical removal may be recommended to reach a definitive diagnosis.

Molecular Testing

When a fine-needle aspiration yields an indeterminate result (Bethesda categories 3 or 4), molecular testing of the biopsy sample can provide additional information. This newer technology looks for genetic mutations and other molecular markers associated with thyroid cancer.^[14] Molecular testing can help doctors and patients make more informed decisions about whether to proceed with surgery or to continue monitoring the nodule with regular ultrasound examinations.

A benign pattern on molecular testing significantly decreases the risk of malignancy in indeterminate thyroid nodules, although these nodules still require ongoing ultrasound surveillance.^[14] Before molecular testing is performed, patients should be counseled about the potential benefits and limitations of the test.^[14] It’s important to note that molecular testing has not yet been validated for use in children or pregnant women.^[14]

Diagnostics for Clinical Trial Qualification

Clinical trials investigating treatments for benign thyroid nodules typically have specific diagnostic criteria that patients must meet to be eligible for enrollment. While the exact requirements vary depending on the particular study, several common diagnostic standards are generally used.

Most clinical trials require confirmation that the thyroid nodule is truly benign before experimental treatments can be tested. This usually means patients must have undergone fine-needle aspiration biopsy with results showing benign cytology (cell characteristics).^[12] In some studies, nodules must be documented as benign through at least one, and sometimes multiple, biopsies to ensure confidence in the diagnosis.

Trials often specify a minimum nodule size for inclusion. For example, some studies require nodules to be at least 2 centimeters in diameter, while others may accept smaller nodules if they are causing symptoms.^[16] The rationale for size requirements relates to the ability to measure changes in nodule volume during treatment, as very small nodules may be difficult to assess accurately for reduction in size.

Documentation of symptoms is frequently required for trial enrollment. Patients may need to demonstrate that their nodules are causing specific problems such as cosmetic concerns (a visible lump or swelling in the neck), compression symptoms (difficulty swallowing or breathing), or hyperthyroidism in the case of functioning nodules.^[13] Some trials specifically target patients who refuse surgery or who have medical conditions that make surgery risky.

Thyroid function tests showing normal or near-normal TSH levels are often required. Studies may exclude patients with significant thyroid dysfunction, as this could affect treatment outcomes and complicate interpretation of results. Ultrasound characteristics are also important—trials may specify whether they are studying solid nodules, cystic nodules, or those with mixed composition.

Before enrolling in clinical trials testing newer treatments such as radiofrequency ablation, patients typically undergo comprehensive ultrasound evaluation to assess nodule location relative to critical structures like the carotid artery and the nerve that controls the voice box (laryngeal nerve).^[16] Nodules located too close to these vital structures may be excluded from certain trials due to safety concerns.

Some trials comparing different treatment approaches require baseline measurements that will be repeated during follow-up. This might include detailed ultrasound measurements of nodule volume, quality of life questionnaires assessing symptom burden, photographs documenting cosmetic appearance, and comprehensive thyroid function testing.^[13] All these baseline assessments help researchers evaluate whether new treatments are effective compared to standard approaches.