Pathology of Follicular Thyroid Adenoma Regarding Malingnant and Regressive Changes

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Based upon the findings of 3 cases with metastasizing adenoma, the histologic features of 7 items as well as vascular invasion were proposed for the evaluation of histologic malignancy of 177 surgical cases with follicular adenoma. Nodular goiters of 29 cases with other types and of 32 autopsy cases and thyroid carcinoma of 90 surgical cases were used for control study. Invasion into the vascular lumen, a sign of unquestionable malignancy, was most frequently accompanied by capsular invasion and further by mitosis, nuclear pleomorphism, clear cells and large nuclei. Any one of the following two items, psammoma bodies and mixed histologic types, was an important sign of malignancy although its incidence was considerably limited.
The features of the above histologic malignancy were frequently observed in the subcapsular regions and had a significant incidence in relation to the size of adenoma and sclerotic lesions of the arterioles with or without muscular cushions surrounding or within adenoma. Regressive changes, e.g. cyst formation, edema, necrosis and fibrosis had the same relation but were frequently found in the central region.