The epitheliomeral concept of the thyroid gland's structural organization

Abstract

The permanent increase in the number of cases of different forms of thyroid pathology requires a deeper study of the thyroid structure and its morphogenetic processes. The thyroid glands of Wistar rats were used in a composite study that involved standard light microscopy, semithin sections, silver staining, immunohistochemistry, morphometry, three-dimensional analysis, and computer-assisted three-dimensional reconstruction. The absolute majority of follicles have from one to seven interfollicular contacts (C) with other neighbouring follicles. The surface of C makes up 32% of the follicular basal surface. In the central zone of 1-micron-thick sections, the relative quantity of C per follicle (0.44 +/- 0.05) is 36% more than in the peripheral zone (0.28 +/- 0.07; P < 0.05). The analysis of serial sections shows that 134 follicles have 133 C. Only three follicles are separate; four form pair groups, and others form groups that include up to 92 follicles. Follicles form linear chains with numerous branches. A three-dimensional reconstruction demonstrates a spatial configuration of the parenchyma's elements. In C, the basement membrane is absent. Consequently, a group of interconnected follicles form a parenchymal compartment with a common basement membrane. We named these parenchymal compartments "epitheliomers." Both the formation of new follicles and follicular fusion take place within the boundaries of the epitheliomer without violating the integrity of the compartment. The fusion of follicles is brought on by the destruction of the epithelium of C. The authors put forward a new "epitheliomeral" concept with regard to the structural organization of the thyroid gland.