Placenta Teratoma or Acardiac Fetus Amorphous: A Case Study by DNA Genotyping.

To date, 40 cases of placental teratoma and 21 cases of umbilical cord teratoma have been reported in the literature. Such entities are purportedly described as originating from ectopically derived totipotential germ cells forming 1 or more of 3 germ layers, similar to teratomas arising in other sites. These entities have been described as distinct from acardiac twins based on the absence of both an axial skeleton and/or separate umbilical cord attachment. We present a case that would be compatible with placental teratoma according to these criteria. However, DNA genotyping analysis of the "teratoma" and its corresponding normal placental tissue revealed an identical genetic profile at all microsatellite polymorphic loci with exception of one locus demonstrating loss of heterozygosity involving 1 of 2 "teratoma" samples tested. Our finding established that the "teratoma" in fact represented a monozygotic acardiac (amorphous) twin with aberrant division of embryogenesis as a continuum of the monozygotic twinning phenomenon. In summary, this is the first case study of so-called placental teratoma by DNA genotyping investigation. We conclude that the diagnostic term "placental teratoma" should be discouraged unless evidence of monozygotic twining can be ruled out by molecular genotyping.