It was part of a large goiter. The story I'm hearing is that the thyroid expands into a goiter for the purpose of capturing more iodine from the bloodstream, and a thyroid tumor is a growth defect of the goiter. It seems to be common to treat goiter and their tumors with iodine.

But my surgeon made no association between the goiter, tumor and hypothyroid at all and she didn't even recommend iodine. There seems to be a lot of divergent opinion among the pros.