Angiomatous malformation of placental chorionic stem vessels and pseudo-partial molar placentas: report of five cases.

Five placentas referred to the Michigan Placental Tissue Registry between 1982 and 1992 exhibited an unusual malformation of chorionic stem vessels. Multiple intestine-like tangles arising from umbilical vessels rested on and entered the chorionic plate. This anomaly appears similar to the "unusual vascular anomaly of the placenta" reported by Lee et al. (Am J Clin Pathol 1991; 95:48-51). In addition, amnionic-type bands were often adherent to the vascular complex. In three cases, clusters of macrocystic villi interspersed by normal placental parenchyma resulted in a partial molar appearance. Two of the infants were stillborn; three were liveborn. Congenital anomalies were not recognized in other organs. Flow cytometric analysis of placental tissue from four specimens disclosed a diploid chromosomal pattern. This rare anomaly complex appears to be a malformation involving the extraembryonic mesoderm rather than a cytogenetic error.