Abstract
PURPOSE: The spleen is a fist-sized largest lymphoid organ located in the left hypochondrium. It has a unique location, embryological and histological structure that differs significantly from other lymphoid organs. The present work was undertaken to study the microscopic and ultramicroscopic histogenesis patterns of the spleen in relation to gestational age. METHODS: The splenic tissue of nine aborted fetuses of various gestational ages was studied. For cytology study, special stains like Masson's trichrome, Periodic Acid-Schiff, and Reticulin were used; immunohistochemical staining was performed with triple antibodies (C-myc, Ki-67, and Ber-H2); and for ultrastructure study, aluminum mounted specimens coated with gold and argon gas were observed under scanning electron microscopy (SEM). RESULTS: Microscopy and immunohistochemistry showed the developmental changes in the spleen from the emergence of the primordium to the end of the embryonic period in all stages of fetogenesis. The spleen primordium of a fetus at the developmental stage of the primary vascular reticulum was seen in the first trimester fetuses. The primordium is comprised mainly of mesenchymal tissue; numerous lymphocytes invading the area surrounding the central artery forming the periarterial lymphoid sheaths (PALS) were seen surrounded by venous sinuses in the early second trimester fetuses. CONCLUSION: The organizational changes in the reticuloendothelial system and microstructure of the spleen during fetogenesis are very crucial to achieving adult morphology in the future. Histogenesis of the fetal spleen follows a multistep process depending upon the gestational age. Any deviation from normalcy may lead to structural and functional abnormality later in life.