[The importance of atypical adenoma of the thyroid gland]

Histological appraisals were made of 8,741 specimens of removed thyroid glands at the Pathologico-Bacteriological Institute of Kaiserin Elisabeth Spital, between 1978 and 1987. Included, according to classification, were 234 atypical adenomas, 47 encapsulated follicular carcinomas, and 158 invasive follicular carcinomas. Atypical adenoma was found to differ histologically from encapsulated follicular carcinoma by non-detectability of vascular invasions. The age distribution of the patients involved failed to provide any conclusive clue to the effect that atypical adenoma was a precursor of encapsulated follicular carcinoma. Females were more often affected than males with atypical adenoma. No recurrence, metastasation nor complaints are recordable at present from any of the surviving patients with atypical adenoma. Patients who died did not reveal any sign indicative of a thyroid disease as cause of death. The five-year survival rate has been 95 per cent for encapsulated follicular carcinoma. Diagnosis of atypical adenoma is not merely a qualitative problem but a quantitative problem as well. Atypical adenoma of the thyroid gland should be classified as a neoplasia in its own right and as absolutely benign.