Basically it is a goiter with excessive production of thyroid hormones with variable clinical manifestations.
it can be diffuse ( as in Graves disease) or nodular.
Gross: The gland is heavy. The parenchyma is soft appears reddish.
Microscopy: Follicles are variably sized, lined by hyperplastic epithelium, which can project into the lumen.
The colloid is scanty as it is used for production of hormones. its pale because of reduction in thyroglobulin. it has scalloped margins as the follicular epithelial cells ‘eat’ 🙂 colloid for the production of hormones!
Variable lymphocytic aggregates can be seen ( suggesting autoimmune reaction), sometimes with germinal centers.