Saltillo, Coahuila, Mexico

This is a case of acrania in a 19-week fetus. The images are transvaginal. Note the large amount of brain matter that distinguishes this condition from anencephaly. Note also that these images infirm the notion occasionally reported in the literature that acrania is a precursor stage of anencephaly. Anencephaly is very commonly detected much earlier then this. Further anencephaly is neural tube defect while acrania is a failure of the mesenchyme to migrate over the neural tube. The recurrence risk of acrania is also negligible compared to that of the neural tube defects.