Your doctor may use several tests to learn the size and location of a thyroid nodule or to help determine if a lump is benign, meaning not cancerous, or malignant, meaning cancerous. Your doctor may order blood tests to check how well your thyroid is functioning.
Ultrasonography is a technique that produces a picture of the thyroid. In this procedure, high-frequency sound waves, which cannot be heard by humans, pass through the thyroid. The patterns of echoes produced by these waves are converted into a picture or sonogram by a computer. Doctors can tell if nodules are fluid-filled cysts, which are usually benign, or solid lumps that might be malignant.
A radioactive iodine scan can outline abnormal areas of the thyroid. Before the scan, you are given a very small amount of a radioactive substance, usually technetium (Tc-99m), which collects in the thyroid. An instrument called a scanner can detect areas in the thyroid that don't absorb iodine normally. Because such "cold spots" can be either benign or malignant, further tests are necessary.
Biopsy, or studying tissue samples under a microscope, is the only sure way to determine if you have thyroid cancer. There are two ways to obtain a sample of thyroid tissue — by withdrawing cells using a needle, called a needle biopsy, or by surgically removing the nodule, called a surgical biopsy. In either case, a pathologist examines the tissue to look for cancer cells.
If the needle biopsy does not detect cancer, your doctor may recommend a surgical biopsy or give you thyroid hormone. Thyroid hormones make it unnecessary for the thyroid to produce its own hormones. The gland, including the nodule, may shrink and become inactive. If the thyroid hormone is not effective, surgical biopsy may be performed.
UCSF Health medical specialists have reviewed this information. It is for educational purposes only and is not intended to replace the advice of your doctor or other health care provider. We encourage you to discuss any questions or concerns you may have with your provider.