Irregular growth of the thyroid — a butterfly-shaped gland at the base of the neck just below the Adam's apple.

A goiter may be an overall enlargement of the thyroid. Or it may be the result of irregular cell growth that forms one or more lumps, called nodules, in the thyroid. In some cases, a goiter might not change the way the thyroid works. In others, it may lead to an increase or decrease in thyroid hormones.

Most people with goiters have no symptoms other than a swelling at the base of the neck. Many goiters are small enough that they're only found during a medical exam or an imaging test for another condition. Other symptoms depend on whether thyroid function changes, how quickly the goiter grows and whether it blocks breathing.

Goiter treatment is based on the size of the goiter, its symptoms and what's causing it. If a goiter is small and thyroid function is healthy, a wait-and-see approach with regular checkups might be recommended. If a goiter is causing thyroid problems, then medication, surgery or radioactive iodine treatment may be options.