A histopathological, immunohistochemical and ultrastructural study of intranuclear cytoplasmic inclusions in thyroid papillary carcinoma.

Intranuclear cytoplasmic inclusions (ICI) in 38 cases of thyroid papillary carcinoma were studied histopathologically, immunohistochemically, and ultrastructurally in order to examine the frequency of ICI and their relationship to both the histological structure and cytological findings in thyroid papillary carcinoma. The fine-structure and biochemical state of ICI were also studied. ICI occurred in all 38 cases. ICI occurrence ranged from one in several microscopic fields to more than ten per field. The number of ICI divided by the number of nuclei on the microscopic photographs ranged from 0.013 to 0.116. The frequency of ICI was strongly influenced by the state of nuclear chromatin and pleomorphism, but was not influenced by a pattern of papillary or follicular tumour growth. Immunohistochemically, 10-30% of ICI revealed strong thyroglobulin (Tg), which was ascertained by immunoelectron microscopy. Neither T3 nor T4 was detected in ICI (with some exceptions). Some ICI showed keratin and vimentin. PAS-positive ICI were observed. Ultrastructurally, enlarged r-ER, many Golgi vesicles and small vesicles (diameter of 300-500 nm) and sacs were observed in ICI. These findings suggested increased protein synthesis and/or protein accumulation. Abundant secondary lysosomes, showing degradation of ICI, and bundles of condensed intermediate filaments were also detected. The character and genesis of ICI are discussed.