Asymmetric parasitic dicephalus conjoined twins.

In this report, we describe the case of a 19-year-old primigravida pregnant woman who had been hospitalized for 2 days with bleeding and a diagnosis of imminent abortion. Sonographic examination revealed a single fetus of approximately 17 weeks' gestation that initially appeared normal except for a mass on its neck. Further evaluation of the mass identified it as an anencephalic fetal head that was joined to the body with deformed cervical vertebrae. We diagnosed asymmetric parasitic dicephalus conjoined twins. The parents elected to terminate the pregnancy. Labor was induced, and the patient delivered a 20-cm, 208-g male fetus. The fetus had 4 normal limbs and a normal abdomen. Both its heads had a cleft lip, and its spine was U shaped with closed spina bifida at the spinal union in the thoracolumbar area. The patterns of conjoined twins are infinitely varied, but they can be generally classified according to standardized terms based on the anatomic site of their union. Cases of conjoined twins occur so rarely that it is important to learn as much as possible from each case.