A holoacardius from a monozygotic, monochorionic twin pregnancy of 36 weeks is described. Trisomy-18 was diagnosed in the viable female cotwin. Computerized tomographic, radiologic, and ultrasonographic procedures were applied to the acardiac. Its three-vessel umbilical cord was velamentously attached to the single placenta. Grossly malformed and poorly developed craniofacial structures, absence of neck and upper extremities, sirenomelic lower extremity, absence of heart, and development of only a few skeletal elements were prominent features. A review of selected world literature emphasizes the limits of the estimates dealing with the total number of reported cases and the incidence of acardii.
