Human fetal thyroid gland: A morphological & histological study

Introduction: the thyroid gland is the first endocrine gland to develop by 24 days after fertilization. It regulates the basal metabolic rate, somatic and psychic growth. The gland promotes growth and development of the brain during fetal life. The embryogenesis of the thyroid gland is important but dealt less in the literature. Therefore, our study aimed to evaluate the morphological and histological features of the thyroid gland in fetuses. Materials and methods: 18 fetuses (9 males & 9 females) of gestational ages ranging from 12-36 weeks were used in the study. The weight of the thyroid gland in grams was measured, and the microscopic features were noted. The size of the thyroid follicles and the colloid present in them were measured using image analyzer software. Results: The fetuses were grouped into three trimesters. The gland was normally bi-lobed connected by an isthmus. However, in one of the fetus, the isthmus was absent. The observation of the histological features revealed that development of the thyroid gland has three stages as Colloid formation stage, folliculogenesis stage, and mature follicular growth stage. These stages were correlated with gestational age. Observations including the first appearance of follicles and follicular colloid as well as the secretory and excretory activities in the gland were made and quantified. Conclusion: the present study provides an insight of the morphological and microscopic alterations during the embryogenesis of the thyroid gland. It will further be useful to understand the anatomical and histopathological changes in the disorders of the thyroid gland.