The fine structure of normal and ectopic (tubal) human placental villi as revealed by scanning and transmission electron microscopy.

The aim of this study was to examine the development of chorionic villous trees during early periods of normal intrauterinal and ectopic (tubal) pregnancies, and to study the structural specializations on the free surface of mature placental villi by scanning and transmission electron microscope (SEM and TEM). In order to study the structures of placental villi between 28 and 34 days old (pc), early, 6-8 week normal and ectopic, and full term human placenta samples were obtained from legal curettage and hysterectomized cases, and spontaneous deliveries, and tissues samples were prepared for SEM and TEM. Three-dimensional configurations of the developing chorionic villous trees were observed as large main villus groups, covered with abundant microvilli of different size and diameters. It appeared that the chorionic villous trees which emerged from the chorionic plate divided gradually into branches of which ramifications originated as buds. These buds gradually grew and were transformed into shoots. The number of developing new villi appeared to increase gradually from 28 days to 9 weeks (pm) of gestation. From the 4th week onwards the massive trophoblastic sprouts were observed on the surface of main chorionic villi which transformed into primary, secondary and tertiary villous trees. When the placental villi formation in ectopic pregnancy was compared with the intra-uterinal pregnancy, an arrested development was remarkable. The configurations of ectopic placental villi seemed to be disparate, such as curved lines or compressed and wrinkled positions so that the three dimensional aspect had been wizened. The ramification and new villi formation seen as in the normal placenta were not only decreased but also infrequent. Some placental villi samples displayed a gradually thinning terminal region. Trophoblastic degenerations were frequently found on the surface of ectopic villi ultrastructurally. According to these results, we comment that in ectopic pregnancy the placental villi formation and development could have been delayed. At term, some specialized structural modifications were observed on the free surface of the mature placental villi. The presence of some dome-like balloonings and many crateriform hollows were the most striking features of the mature intermediate and terminal villi. According to the increasing physiological needs of the growing fetus, these special structures that are related to lung-like and kidney-like functions and named "nephropneumonic-like units", formed in the mature placental barrier. We have observed that these special units were showing a smooth surface similar to an inflated balloon.(ABSTRACT TRUNCATED AT 400 WORDS)