Solid or fluid-filled lumps that form within the thyroid — a butterfly-shaped gland at the base of the neck just below the Adam's apple.

Most thyroid nodules aren't serious and don't cause symptoms. Only a small percentage of thyroid nodules are cancer. Most people don't know that they have a thyroid nodule until it's found during a routine medical exam or on a scan done for another health reason.

Most thyroid nodules don't cause symptoms. But some nodules may grow large enough to be felt or seen. A large nodule can cause shortness of breath or swallowing problems. Some thyroid nodules make hormones. That can cause a disorder called hyperthyroidism. It triggers symptoms such as weight loss, sweating, tremor and an irregular heartbeat.

Treatment depends on the type of thyroid nodule. If a nodule is small and not cancer, the condition may be monitored without treatment. If a thyroid nodule makes hormones, treatment with medicine or surgery may be recommended. Treatment for a nodule that's cancer usually involves surgery.