Fetus amorphus or placental teratoma?

A differential diagnosis between fetus amorphus and placental teratoma based on the presence of an umbilical cord and/or skeletal organization in the fetus amorphus has been proposed (Fox and Butler-Manual: Journal of Pathology 88:137-140, 1964). We report a description of one new case of fetus amorphus, along with the results of a critical reexamination of 96 cases from the literature. Our findings fail to support the proposed criteria for distinguishing fetus amorphus from placental teratomas. We find that the presence or absence of an umbilical cord does not relate at all to the developmental state of the specimen. The extent of skeletal development may be a more valid criterion; however, the internal organization in the fetus amorphus forms an anatomical continuum with that of the placental teratoma, making a differential diagnosis meaningless. Additional research is necessary to solve this dilemma.