Background: The thymus is one of the primary lymphoid organs other than being the bone marrow. It is responsible for the provision of thymus-processed lymphocytes (T lymphocytes) to the whole body. Aim of the study: To study the microscopic architecture of the cortex and medulla, structure and type of epithelial cells, nature of connective tissue stroma, vasculature of thymus organ, the morphology of Hassall Corpuscle (HC). To study the histometric analysis like estimation of volume and diameter of HC at various gestational age. Method: Total 20 aborted and still born fetuses ranging from 17-39 weeks of gestation were used for the study. After embalming, meticulous dissection, thymus gland was weighed and fixed with formalin. The various histological and histometric parameters were observed. Results: The cortex and medulla were well demarcated by the 17th week. The weight and volume of the thymus were proportionately increased as the fetal age advanced. Early phase had thick mucoid interlobular septae whereas the later phase had thin, reticular interlobular septae. Four different types of HC (SHC, CHC I, CHC II and DHC) in fetus were seen. The presence of solid HC at the periphery of the medulla and degenerating HC at the central core of the medulla tends to postulate the direction of maturation which is from the periphery to the center of the medulla. Conclusion: The findings of the present study is in conformity with studies related to the volume and size of the thymus with respect to gestational ages and histological features related to parenchymal and mesenchymal tissue composition and its various components. However, the present study noted different types of Hassall’s Corpuscles which are reported in the adult thymus and the findings lead to further discussion on the maturation and differentiation of Hassall’s Corpuscles in human fetal thymus.
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