Ultrastructure of the tubal chorion.
The chorion of five cases of ampullar pregnancies aged 9-11 weeks was examined in electron microscope. The appearance of chorion is affected by massive haemorrhage into the tubal lumen which occurs in this type of tubal pregnancy and causes its segregation from the tubal wall. The chorionic villi scattered in haematoma show different structure. The electron microscope investigation reveals that many chorionic villi possess the intact microvillous surface and are similar to normal villi of the intrauterine chorion. The development of syncytiotrophoblastic organelles especially as far rough endoplasmic reticulum, Golgi apparatus and mitochondria suggests that the syncytiotrophoblast may for some period be functional under these unfavourable conditions. The chorionic villi imprisoned in blood clot are often covered by fibrin deposits, their syncytium shows considerable folded nuclei with coarse chromatin aggregations, extremely dilated and degranulated endoplasmic reticulum. When syncytium degenerates the fibrinoid sheets invest the isolated portions of the villi. The necrotic villi as well as the cells of cytotrophoblastic islands are embedded in the fibrinoid masses. The cytotrophoblastic cells resembling the cells of basal plate in placenta are found in the tubal wall adjacent to the haematoma.