Morphologic and functional substrate of thyrotoxicosis caused by nodular goiters.

The pathogenesis of nonimmunogenic thyrotoxicosis caused by nodular goiters--with the exception of true toxic adenoma--was investigated in 11 patients by means of scintigraphic, morphologic and autoradiographic technics. The basic event is the appearance, for unknown reasons, of autonomously functioning follicles which are morphologically indistinguishable from normal follicles. Four basic patterns of intrathyroidal distribution of autonomously functioning follicles are individualized: Type I = multiple individual autonomously functioning follicles scattered throughout the goiter. Type II = clustered autonomous follicles without demarcation from less active parenchyma. Type III = multiple microadenomas. Type IV = autonomous function of the majority of all follicles. In all four types, the autonomous follicles occur without recognizable relation to nodule boundaries. Scintiscans cannot predict the microstructure of these types of goiters. More than one pattern of distribution of autonomously functioning follicles may occur within a single goiter. The growth of thyroid nodules is independent of, and certainly not a prerequisite to, thyrotoxicosis. Rather, the appearance of thyrotoxicosis in this type of multinodular goiter depends on (1) the number of autonomous follicles throughout the gland and (2) their mean hormone-producing capacity per unit of time.