Placental teratoma or acardius amorphus with amniotic band syndrome.

The differential diagnosis between placental teratoma and fetus acardius may be difficult. Both are rare conditions and show a variable degree of organisation. Important diagnostic features are the presence or absence of an umbilical cord and craniocaudal development. The presence of an umbilical cord and obvious craniocaudal development is highly indicative of fetus acardius. A fetus acardius is a malformed member of a monochorial twin. An acardius is probably caused by overpowering of the heart of the fetus acardius by that of the normal sibling or primary agenesis of the heart. Our case illustrates the difficulties in making the right diagnosis. Careful analysis showed that most probably amniotic rupture followed by formation of amniotic bands had resulted in the development of a fetus acardius.