The thyroid--a butterfly-shaped gland in the lower neck--can become enlarged for many reasons, some of which are relatively insignificant and some a cause for concern, reports MayoClinic.com. An enlarged thyroid--which is called goiter--indicates that the gland is producing too much or too little thyroid hormone, which regulates the body's metabolism.
Grave's Disease
In Grave's disease, immune system antibodies mistakenly attack the thyroid, explains MayoClinic.com. In response, the gland swells and becomes overactive, which is called hyperthyroidism. If untreated, hyperthyroidism can lead to heart problems and osteoporosis. Some people with Grave's disease develop swollen eyes and faulty vision.
Thyroid Storm
People with hyperthyroidism are at risk for sudden overactivity of the thyroid gland, which is called thyroid storm or thyrotoxic crisis, reports the Merck Manual. This life-threatening emergency, which strains the heart and can result in coma, is triggered by injury, surgery or poorly managed diabetes. It develops in people whose overactive thyroid is untreated or poorly treated.
Hashimoto's Disease
The thyroid gland also swells when it is underactive, which is called hypothyroidism, explains MayoClinic.com. Hashimoto's disease is a disorder in which the body's own immune system attacks the thyroid, but in this case, unlike Grave's disease, the damaged gland produces too little thyroid hormone. If left untreated, hypothyroidism can cause birth defects if a mother has it during pregnancy and myxedema, a rare, life-threatening drop in thyroid production.
Thyroid Cancer
An enlarged thyroid may indicate thyroid cancer, particularly if the swelling is present on just one side of the gland, reports MayoClinic.com. People should keep in mind however, that benign tumors of the thyroid--which also cause swelling--are much more common than cancerous ones.
