Congenital hydranencephaly/porencephaly due to vascular disruption in monozygotic twins.

Monozygotic twinning has been associated with a variety of vascular disruptive defects including congenital hydranencephaly/porencephaly. Data involving 24 cases of congenital hydranencephaly/porencephaly associated with twinning are reported. In these cases, the finding of a preponderance of monozygotic twins and the common association of a deceased co-twin support the hypothesis of a vascular disruptive etiology. These defects are presumed to be secondary to embolic phenomena or thromboplastin release from the deceased co-twin to the survivor via the vascular interconnections of a conjoined monochorionic placenta. In all cases of hydranencephaly/porencephaly, a careful examination of the placenta and membranes for evidence of a deceased co-twin is warranted prior to providing recurrence risk counseling.