Prevalence:

• 1 in 100 births.
• More common in males than females: 4 to 1.

Ultrasound diagnosis:

• Head circumference >2 standard deviations.

Associated abnormalities:

• Types of macrocephaly:
  • Familial (majority of cases): benign, normal neurological development.
  • Secondary: due to an underlying disorder (e.g. hydrocephalus, brain tumor).
  • Megalencephaly: disorder of neuronal and glial proliferation which causes overgrowth of cells and results in severe neurodevelopmental delay. Over 100 syndromes with prenatal or postnatal overgrowth have been described. The most common is Sotos syndrome (autosomal dominant but 95% of cases are due to de novo mutations; macrocephaly, frontal bossing, hypertelorism).

Investigations:

• Detailed ultrasound examination, including neurosonography.
• Fetal MRI.
• Invasive testing for karyotyping and array. Megalencephaly is associated with large deletion of various chromosomes as well as microdeletions.

Follow up:

• Follow-up should be standard.

Delivery:

• Standard obstetric care and delivery.
• Method: cesarean section if the fetal head circumference is >40 cm.

Prognosis:

• Familial macrocephaly: normal neurological development.
• Secondary macrocephaly: depends on underlying condition.
• Unilateral or bilateral megalencephaly: developmental delay and intractable seizures.

Recurrence:

• Familial macrocephaly (autosomal dominant inheritance pattern): 50%.
• Secondary: no increased risk of recurrence.
• Most syndromes have an autosomal dominant inheritance pattern but more than 95% are due to de novo mutations.