Development of the human fetal adrenal gland during the first trimester

The adrenal gland consists of two distinct parts with different embryological origins and functions. The cortex, which originates from the mesoderm, is essential for steroid secretion, while the medulla, derived from neural crest cells, is responsible for catecholamine synthesis. Significant developmental changes in these structures occur during the first trimester, laying the foundation for vital endocrine functions. This study investigates the histomorphological development of the fetal adrenal gland during the first trimester, with a focus on cortical thickness, cellular arrangement, vascularity, and clump formation, to provide insights into this early developmental period. This descriptive study analyzed adrenal glands from first-trimester missed aborted cases. Formalin-fixed, paraffin-embedded tissues were sectioned, stained, and examined under a microscope to assess histomorphological features. The fetal adrenal cortex was observed in all cases, with incomplete separation of cortical layers noted in 45.5%. Clump formation was present in 54.5% of cases, particularly within the zona glomerulosa. The medulla was identifiable in all samples and displayed densely packed cells in 72.7% of cases. Vascularity, the fibrous capsule, and trabeculae were well developed. The average cortical thickness measured 253.15 ± 138.22 μm, with the zona fasciculata being the thickest layer. The average medullary thickness was 222.89 ± 113.64 μm, and the medulla to cortex thickness ratio was 0.93 ± 0.45. This study highlights key aspects of adrenal gland development during the first trimester, emphasizing cortical and medullary differentiation, clump formation, thickness, and vascularization.