Acrania is best described as which of the following?

• A. Abnormal migration resulting in absence of the skull with brain present
• B. Absent brain with an intact skull
• C. Absence of the corpus callosum
• D. Destruction of brain tissue due to vascular insult

Answer: (A)

Acrania refers to a congenital failure of the skull vault to form while the brain tissue develops normally. This happens because the processes that create and ossify the calvarial bones (often involving cranial neural crest cells) are disrupted during early embryogenesis, so the skull bones are absent but the brain is present. This makes acrania distinct from conditions where the brain is absent or severely destroyed (for example, an absent brain with an intact skull or acquired brain injury from vascular insult). In imaging, you’d see a missing calvarium with brain tissue visible but unprotected, highlighting that the skull failed to form while the brain did.