An acardiac acephalic monster.

A case of an acardiac acephalic monster is described, and the literature concerning the incidence, classification and etiology of acardia is reviewed. Acardia is a very rare congenital anomaly occurring in less than 1 in 34600 deliveries. The acardiac monster has been reported only in multiple, monochorionic pregnancies. This bizarre anomalous fetus is sustained in utero by parasitic anastomoses to the circulation of its usually normal co-twin and is therefore not compatible with extrauterine survival. Possibilities for prenatal diagnosis and complications during pregnancy and delivery are considered.