Prevalence:

• 1 in 1,000 at 12 weeks’ gestation.

Ultrasound diagnosis:

• Absence of cranial vault and cerebral hemispheres.
• At 12 weeks acrania is suspected by absence of the normally ossified skull and distortion of the brain (exencephaly). At >16 weeks the brain is destroyed (anencephaly).

Associated abnormalities:

• Chromosomal defects in isolated acrania are rare.
• CNS or other defects are found in about 50% of cases, including spina bifida in 25%.

Investigations:

• Detailed ultrasound examination.

Follow up:

• If the pregnancy continues, follow-up should be standard.

Delivery:

• Standard obstetric care and delivery.

Prognosis:

• Lethal condition with death within the first week of life.

Recurrence:

• One previous affected sibling: 5%.
• Two previous affected siblings: 10%.
• Supplementation of the maternal diet with folate (5 mg/day) for 3 months before and 2 months after conception reduces the risk of recurrence by about 75%.