What is a enlarged heterogeneous thyroid?

Probably thyroiditis: It probably means you have had episodes of thyroid inflammation or thyroiditis. It's generally not a problem unless thyroid function declines below normal or you form nodules that may need to be studied to insure that they're not cancerous. Check w/your doctor.

GOITER: Enlarged thyroid = goiter. Heterogeneity just implies that the features are not uniform. One can see that in inflammatory conditions like hashimoto's thyroiditis, multinodular goiter or even in graves' disease. It is just just a descriptive terminology.