[Pathology of the placenta. X. Syncytial proliferation, calcification, cysts, pigments and metabolic disorders].

Part X of this review is devoted to the remaining pathologico-anatomic patterns which are associated with regressive alterations. Increased syncytial proliferation is the most important aspect within that complex, since it may be a consequence of intervillous and intravillous hypoxia and may thus provide a clue to effects of that kind. Placental calcification may be subdivided by two major groups. The first is relating to "dystrophic" calcification following the same rules in the placenta as it does in other places, in other words, it is calcification of necrotic tissue portions or acidotic areas of decreased circulation. Calcification may just as well occur to particular structures of the placenta, such as the epithelial basal membrane, syncytial proliferations or in walls of vessels. Placental cysts usually are localized at the placental base (in septa), their development being owed to hypoxic events during ontogenesis. They actually are pseudocysts. Placental icterus (along with severe maternal icterus) is macroscopically identifiable with unambiguity. The biliary pigment, histologically, is localized in HOFBAUER cells. Additional reference is made to melanin deposits (in concomitance with congenital giant naevus) and placental alterations in conjunction with rare metabolic disorders.