Antenatal ultrasonic evaluation of acardiac monsters.

Acardiac monster represents a rare but serious complication of monozygotic twin pregnancy. Antenatal recognition is important because of accompanying obstetrical problems, including polyhydramnios, dystocia, and uterine rupture. While pathologic findings are varied, characteristic sonographic findings allow accurate prenatal diagnosis. Acardia must be distinguished from sacrococcygeal teratoma, omphalocele and macerated fetus.