[Signet-ring-cell adenoma of the thyroid: description of a case and review of the literature].

An occasional finding of a signet-ring cell type adenoma, occurring in a 81-year-old man, suffering from inoperable pharyngo-laryngeal carcinoma, is described. Multinodular thyroid parenchyma was excided in performing tracheostomy and histologically examined. On the basis of extensive morphological, histochemical and immunohistochemical observations and of reviewed literature, an unifying morphogenetic interpretation of the signet-ring cell transformation is proposed, with special reference to the pathogenesis of this cytotype and the significance of the cytostructural and cytometabolic characteristics. Problems related to the differential diagnosis and clinicopathological correlation are also discussed.