Acrania is a rare lethal congenital anomaly characterized by an absence of the calvaria.


The estimated incidence is at ~1:1000 pregnancies .


The condition is thought to result from abnormal migration of mesenchymal tissue, which normally covers the cerebral hemispheres. The calvarial bones are partially or entirely absent with relative (albeit abnormal) preservation of development of the cerebral hemispheres. A thin membrane surrounds the cerebral hemispheres.

Radiographic features

Antenatal ultrasound

As the ossification of the fetal cranium begins and accelerates after nine weeks, antenatal ultrasound allows diagnosis from 11 weeks onwards. It is important to look specifically for frontal bone ossification in the axial and coronal planes.

Treatment and prognosis

Acrania is lethal and can progress to anencephaly through the acrania-anencephaly sequence .

Differential diagnosis

Imaging differential considerations include conditions such as: