**5. Pathology**

Grossly the thyroid gland is diffusely enlarged with smooth and hyperemic surface. Rarely the gland is grossly nodular. Consistency of the gland varies from soft to firm. Pyramidal lobe is often prominent.

Microscopically both hypertrophy and hyperplasia are seen. Follicles are small with scanty colloid, and lined by hyperplasic columnar epithelium which can give a pseudopapillary appearance. Vascularity of the gland is increased. There is varying degree of infiltration by lymphocytes and plasma cells. T cells predominate in the interstitium, whereas B cells and plasma cells predominate in lymphoid follicles.

On electron microscopy there is increased golgi reticulum and mitochondria, and it is also characterized by presence of prominent microvilli.

After treatment with antithyroid drugs and radioiodine, the vascularity of the gland decreases, follicles enlarges and filled with colloid, and papillary projection regresses.
