Ultrastructural pathology in Hashimoto's thyroiditis.

Ultrastructural studies of the thyroid tissue in two cases of Hashimoto's thyroiditis demonstrated that the inflammatory cells do not pass through the follicular cells. Indeed these cells travelled between the epithelial cells in a manner similar to the neutrophil emigration (diapedesis) through the vessel wall in acute inflammation. Inflammatory infiltrates were composed of lymphocytes, plasma cells, or transformed lymphocytes that showed features intermediate between those of lymphocytes and plasma cells. These inflammatory cells were observed to travel from the stroma to the follicular lumen in a vectorial manner - similar to neutrophilic chemotaxis in acute inflammation. The basement membrane around the thyroid follicles remained intact around some follicles whereas it was reduplicated or focally increased in thickness around others. The basement membrane material seemed to have been secreted by the follicular cells, and strands of early collagen fiber formation were seen within the excess basement membrane material. The follicular cells showed evidence fo sublethal injury characterized by prominent defects of the rough endoplasmic reticulum or the mitochondria. Cells from areas that appeared as foci of squamous metaplasia by light microscopy showed an increased number of cytoplasmic filaments (120 to 160 A), bundles of tonofilaments, large desmosomes, an increased number of desmosomes, and intracellular desmosomes. The colloid content of the follicles was diminished, and it seemed that instead of secreting the protein colloid, the follicular cells in Hashimoto's thyroiditis were producing either excessive proteinaceous material similar to colloid or other types of proteins such as basement membrane material or keratin.