What does diffusely enlarged heterogeneous thyroid gland mean?

Graves/Thyroiditis. Most commonly this is due to graves disease or thyroiditis. In both of these cases your immune system attacks your thyroid and tries to kill it, because it thinks it is foreign, like a virus. However in graves disease the antibodies that attack the thyroid actually stimulate receptors that make it grow and produce too much thyroid hormone. In thyroiditis the immune cells infiltrate the thyroid.