Primary Acalvaria is an extremely rare malformation characterized by the absence of the flat skull bones of the brain, dura mater, and scalp muscles. The skull base and facial features are fully formed and usually appear normal. The cause of Acalvaria is still unknown. Acalvaria can be distinguished from anencephaly, the most common differential diagnosis, by the presence of a layer of skin overlying the brain matter and normal cerebral hemispheres.