With goiter it's often a resident infection causing the tissue to reproduce uncontrolled.
Iodine allows the thyroid tissue to break itself down to maintain a proper-size gland (Periodic table labels it 'I'). I. is used by the body in checking DNA to see if the cells in this or that tissue of the body are functioning according to instructions, and when they are nearing the end of their encoded lifespans. Viruses and bacteria have the ability to inject foreign DNA strands and mess with the mechanisims to adapt the tissues to make themselves a more comfortable environment- which is often the case with goiters.
Halide imbalance is often a complicating factor in such a situation, in countries where bromides and flourides are used a lot in food, water and textile industry. The body prefers a higher level of Iodine and chlorides (see the salt molecule) vs florides and bromides.
Take care if this info leads you to research further into Iodine supplementation- Iodine triggers bacterial dieoff in the body tissues, and can be very rough without first undergoing parasite cleansing and having the iodine cofactors available at home(see the description of the VWT Iodine Forum for links to the full iodine protocol, or see the 'stop the thyroid madness' site via a google search).