Ductal metaplasia in chronic lymphocytic thyroiditis as a manifestation of phylogenic regression to an exocrine structure.

From a morphologic and functional point of view the thyroid can be considered as both an exocrine and endocrine organ. Firstly, thyroglobulin is secreted at the apical pole of the thyrocyte. Secondly, after endocytosis thyroglobulin is lysed and T3 and T4 are secreted at the basal pole into the bloodstream. However, usually exocrine glands are constituted of 2 well separate components: an acinus/alveolar component and an exocrine duct component. Under particular conditions such as chronic injury the acinus/alveolar component is rapidly destroyed, whereas the ductal component seems to be far more resistant and can proliferate giving rise to a tubular network described as "ductulus reaction" or "ductal metaplasia." Normal exocrine ducts and metaplastic ducts exhibit common genetic and phenotypic features directly related to their tubular morphology. In this study, we describe in lymphocytic autoimmune thyroiditis the appearance of ductal-like structures which displayed the features of ductal metaplasia.