Acardia syndrome coexisting with gastroschisis in the co-twin.

Acardia syndrome is a rare complication affecting monozygotic twins, wherein one twin fails to develop brain and thoracic structures, while the co-twin most often develops normally. In this report we present an acardiac anencephalic monozygotic twin with an omphalocoele and a co-twin with severe intrauterine growth retardation and gastroschisis. The presence of gastroschisis in the co-twin of an acardiac foetus is rare. The embryologic basis of the twin reversed arterial perfusion (TRAP) sequence is outlined and the observed anomalies in the co-twin traced to a similar pathophysiology.