Missed our latest free live-stream? Catch up now on our Procedure Tips (Chris Nicholas) and Right Lower Quadrant Pain (Matt Morgan)


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

The estimated incidence is at ~1:1000 pregnancies 4

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.

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.

Acrania is lethal and can progress to anencephaly through the acrania-anencephaly sequence 8.

Imaging differential considerations include conditions such as:

Article information

rID: 12140
Tag: cases, cases
Synonyms or Alternate Spellings:
  • exencephaly
  • Absent fetal skull
  • Absent fetal calvarium

ADVERTISEMENT: Supporters see fewer/no ads

Cases and figures

  • Case 1
    Drag here to reorder.
  • Case 2
    Drag here to reorder.
  • Updating… Please wait.

     Unable to process the form. Check for errors and try again.

     Thank you for updating your details.