Ultrastructure of the nidatory site in tubal pregnancy

Nidatory site of pre-abortive tubal pregnancy, obtained from 41 years old women was studied in both scanning and transmission electron microścopes. The nidatory site was basically composed of anchoring villi, trophoblastic column and shell, fibrinoid layer and marked round cell infiltration. In spite of the histologically normal appearance of the chorionic villi, villous syncytiotrophoblast ultrastructurally showed slight tendency of degeneration, being concurrent with blighted ovum. The trophoblast at the trophoblastic column and shell contained a great amount of glycogen which decreased at the distal part near and in the fibrinoid layer. The degenerating trophoblast were surrounded by massive fibrin bundles and fibrin bundles and fibrin-like deposits. The more the degeneration of the trophoblast proceeded, the more the fibrin deposits accumulated around the trophoblast. The trophoblast which ran over the fibrinoid layer was scarcely observed and if there, it showed marked degenerative appearance. These findings suggest the possible role of fibrinoid layer: protection of maternal tissue from trophoblastic invasion, not the protection of fetus from maternal immunological attack. No direct contact such as tight junction, desmosome and so on between trophoblast and maternal cell was observed in the present study, suggesting the formation of special connection with the allogeneic cell, one of the unique characters of the trophoblast, is expressed only when it is primitive in the early stage of development.