Acrania is a rare congenital disorder that occurs in the human fetus in which the flat bones in the cranial vault are either completely or partially absent.

[2] Recent work has identified mutations in the hedgehog acyltransferase (HHAT) gene that have caused acrania along with holoprosencephaly and agnathia.

Disruption of these pathways leads to abnormal bone and cartilage formation causing acrania and multiple other craniofacial patterning problems.

ABS occurring in the developing brain neural tissue is one cause of acrania.

The hindbrain proceeds to develop normally, allowing for the child to be carried to term, but the diencephalon and ocular lobe remain small and underdeveloped.

When ectodermal mesenchyme fails to migrate into the head region of the embryo, the skull will not be able to form.

A presence of brain tissue will confirm the diagnosis of acrania and differentiate it from other developmental problems such as anencephaly.