Scanning electron microscopic study of the collagen sheath of the human thyroid gland and its disorders

A cell-maceration/scanning electron microscope (SEM) method was employed to demonstrate the collagen sheath around follicles (perifollicular sheath) of the human thyroid gland and its disorders. In the normal thyroid gland, the follicles were surrounded by spherical collagen sheaths composed of a framework of thick collagen bands 1-5 microns in width and fine solitary collagen fibrils 50-70 nm in diameter. In benign thyroid diseases (Graves' disease, Hashimoto's thyroiditis and adenomatous goiter), the perifollicular sheaths differed in size and in shape according to the disease, but they were always composed of thick collagen bands and fine fibrils as in the normal thyroid. On the other hand, the spaces surrounded by the perifollicular sheaths varied markedly in size in follicular adenoma, were small in oxyphilic adenoma, and irregularly shaped in embryonal adenoma. In all these adenomas, the perifollicular sheaths were mainly composed of fine fibrils 35-45 nm in diameter. In follicular carcinoma, the size and shape of the space surrounded by the perifollicular sheaths were irregular. In papillary adenocarcinoma, the collagen sheaths showed a papillary pattern. In medullary carcinoma, tumor nests were surrounded by well developed collagen sheaths. In all these carcinomas, the collagen sheaths were mainly composed of fine collagen fibrils 32-45 nm in diameter. In adenomas and follicular carcinoma, the perifollicular sheaths frequently had large holes through which the spaces surrounded by the collagen sheaths connected to each other. Such holes were, however, rare in the normal thyroid and benign non-neoplastic thyroid diseases.