A noncancerous enlargement of the thyroid gland. With a goiter, the levels of thyroid hormones may be normal (euthyroid), elevated (hyperthyroidism), or decreased (hypothyroidism).

Not all goiters cause signs and symptoms. When signs and symptoms do occur they may include:

A visible swelling at the base of your neck that may be particularly obvious when you shave or put on makeup
A tight feeling in your throat
Coughing
Hoarseness
Difficulty swallowing
Difficulty breathing

Iodine Deficiency and Autoimmune Disorders

Globally, the most recognized cause of thyroid goiter has been due to iodine deficiency, however, it is rare in the US since there is plenty of iodine in drinking water and certain foods we eat like table salt. Goiters could be caused also by thyroid nodules.
Hashimoto’s thyroiditis is the next most common cause in countries that use iodized salt. Goiter could also result in cyanide poisoning which is particularly common in tropical countries where people like eating cyanide-rich cassava root in staple food.

Goiter treatment depends on the size of the goiter, your signs and symptoms, and the underlying cause. Your doctor may recommend:

Observation. If your goiter is small and doesn't cause problems, and your thyroid is functioning normally, your doctor may suggest a wait-and-see approach.
Medications. If you have hypothyroidism, thyroid hormone replacement with levothyroxine (Levoxyl, Synthroid, Tirosint) will resolve the symptoms of hypothyroidism as well as slow the release of thyroid-stimulating hormone from your pituitary gland, often decreasing the size of the goiter.

For inflammation of your thyroid gland, your doctor may suggest aspirin or a corticosteroid medication to treat the inflammation. For goiters associated with hyperthyroidism, you may need medications to normalize hormone levels.

Surgery. Removing all or part of your thyroid gland (total or partial thyroidectomy) is an option if you have a large goiter that is uncomfortable or causes difficulty breathing or swallowing, or in some cases, if you have a nodular goiter causing hyperthyroidism.

Surgery is also the treatment for thyroid cancer.

You may need to take levothyroxine after surgery, depending on the amount of thyroid removed.

Radioactive iodine. In some cases, radioactive iodine is used to treat an overactive thyroid gland. The radioactive iodine is taken orally and reaches your thyroid gland through your bloodstream, destroying thyroid cells. The treatment results in diminished size of the goiter, but eventually may also cause an underactive thyroid gland.

https://www.medicinenet.com/script/main/art.asp?articlekey=3615
https://www.mayoclinic.org/diseases-conditions/goiter/symptoms-causes/syc-20351829
https://www.mayoclinic.org/diseases-conditions/goiter/diagnosis-treatment/drc-20351834