Congenital microcephaly due to vascular disruption: in utero documentation.

Death in utero of one member of a monozygotic twin pair has been associated with vascular disruptive phenomena in the surviving twin. It has been hypothesized that this event initiates clot formation in the surviving twin with consequent necrosis of tissues distal to the occluded vessels. This case report describes onset in utero of multicystic encephalomalacia and microcephaly in a surviving twin whose brain appeared normal on ultrasound scanning before death of the cotwin at 21 weeks' gestation. The case provides further support for the hypothesized pathogenetic sequence and illustrates the importance of reviewing all prenatal ultrasound scans in infants with congenital microcephaly.