Prevalence:

• 1 in 20,000 births.

Ultrasound diagnosis:

• Increased interorbital diameter >95^th percentile.

Associated abnormalities:

• Chromosomal defects, mainly trisomy 13, are very rare.
• Genetic syndromes are found in >50% of cases. The most common are frontonasal dysplasia (sporadic; hypertelorism, midline facial cleft, abnormalities of the nose, cranium bifidum ocultum), craniosynostosis (including Apert, Carpenter, Crouzon) and Neu-Laxova syndrome (autosomal recessive; hypertelorism, microcephaly, agenesis of corpus calosum, contractures in the upper and lower limbs, fetal growth restriction).
• Associated defects: frontal encephalocele and agenesis of the corpus calosum.

Investigations:

• Detailed ultrasound examination.
• Invasive testing for karyotyping and array.

Follow up:

• Isolated: follow-up should be standard.
• Syndromic: antenatal care should be adjusted according to the risks of the condition.

Delivery:

• Standard obstetric care and delivery.

Prognosis:

• Isolated: generally good but in severe cases the cosmetic implications are important. There might be impaired stereoscopic binocular vision.
• Syndromic: generally poor with high risk of neurodevelopmental delay.

Recurrence:

• Isolated: no increased risk of recurrence.