[Features of the pathogenesis of the placenta growing in the scar after cesarean section].

Objective: to investigate the structural and pathogenetic features of pathological placental attachment in the scar after cesarean section.

Material And Methods: The investigators explored 12 uteri; 11 of which were removed with placentas at 9 to 38 weeks' gestation (one in the first trimester, three at 18-22 weeks, two at 32-35 weeks, and five at 37-38 weeks); one uterus was removed after an artificial abortion at 12 weeks' gestation in the scar, as well as the scars excised in the first trimester in non-developing (n=4) and progressive (n=2) pregnancies. For histological examination, fragments of the full-thickness uterine wall were taken from the placental bed in different areas. The sections were stained for fibrin with hematoxylin and eosin, van Gieson stain, and the Martius scarlet/blue (MSB) technique. Decidual tissue, trophoblast, vascular component, and smooth muscle tissue were identified by an immunohistochemical assay using antibodies to vimentin, pan-cytokeratin, vascular endothelium (СD31), and smooth muscle actin.

Results: In most cases, placental localization in the scar after cesarean section was accompanied by abnormal placental attachment: almost always placenta accreta, less frequently in combination with its ingrowth (placenta accreta/increta). The morphological substrate of placenta increta was a change in the content and ratio of normal histological components in the uterine wall, such as the mucosa, smooth muscle tissue, and vessels (the absence or thinning of decidual tissue and the myometrium, as well as its cicatricial changes). The structural criterion for placenta increta was necrosis of the walls of the large veins in the myometrium due to the replacement of their intermediate trophoblast and fibrin and to the destruction of vessel walls, leading to prolapse of the chorionic villi into the veins.

Conclusion: In most cases, placental localization in the scar after cesarean section is accompanied by abnormal placental attachment: placenta accreta, less frequently in combination with its ingrowth (placenta accreta/increta).