Chorion nodosum: a placental feature of the severe early amnion rupture sequence.

A lesion of placental membranes and/or chorionic disc mesenchyme found in 4 of 13 cases of the limb-body wall complex (LBWC) and in 1 case of term extraamniotic pregnancy, named chorion nodosum (ChN), is described. All five ChN cases were associated with amniotic bands. Although grossly inapparent and histologically superficially similar to amnion nodosum, ChN is a distinct flat lesion located in the chorion denuded of amnion, occurring in different clinical settings, and most probably having a different pathogenesis, because it has bimodal gestational age distribution and occurs earlier in pregnancy when associated with LBWC, and only in the LBWC cases associated with amniotic bands. Therefore, not only oligohydramnios but also other factors involved in etiopathogenesis of LBWC are most probably operative in ChN, such as early vascular disruption, direct contact of the chorion denuded of amnion with fetal body, or a metabolic defect of fetal epidermis and amnionic epithelium. Prolonged severe oligohydramnios most probably plays main role in the pathogenesis of ChN in term extraamniotic pregnancy.