Grossly, thyroid enlargement in Hashimoto's thyroiditis (HT) is generally symmetrical, often with a characteristic conspicuous pyramidal lobe. The tissue involved by HT is pinkish-tan to frankly yellowish in color and tends to have a rubbery firmness. There is no necrosis or calcification. The capsule is intact and non-adherent to peri-thyroid structures. Microscopically, there is a diffuse process consisting of a combination of epithelial cell destruction, lymphoid cellular infiltration, and fibrosis. Lymphocytes are predominantly T-cells and plasma cells. Most infiltrating T-cells have α/β T-cell receptors. Gamma/delta T-cells are rare. Hashimoto's thyroiditis has been graded based on lymphocytic infiltration seen on cytology, into Grades 0-III, where Grade 0 means no lymphoid cells and Grade III severe lymphoid cell infiltration. Deposits of dense material representing IgG are found along the basement membrane on electron microscopy. This chapter explores the pathology of Hashimoto's disease.
Pyramidal Lobe
