Prevalence:

• 1 in 100,000 births.

Ultrasound diagnosis:

• The whole or parts of the surface of the brain appear smooth with lack of development of brain folds (gyri) and grooves (sulci).
• Prenatal diagnosis is very difficult but suspicion could be raised >24 weeks’ gestation. The parieto-occipital and Sylvian fissures appear flat and the subarachnoid space is usually increased.
• In all cases of apparently isolated brain abnormalities, such as ventriculomegaly and agenesis of the corpus callosum, a detailed follow-up scan should be arranged at around 26 weeks to exclude an underlying lissencephaly.
• There are 2 types of lissencephaly:
  • Type I: agyria with lack of neuronal migration. The cortex is smooth and thick.
  • Type II: extensive and anarchic migration with lack of layering. The cortex is described as “cobblestone”.

Associated abnormalities:

• Chromosomal abnormalities: no increased risk.
• The condition can occur on its own, but it is commonly associated with genetic syndromes:
  • Miller-Dieker: sporadic; type I lissencephaly, microcephaly, heart defects, polydactyly.
  • Walker-Warburg: autosomal recessive; type II lissencephaly, agenesis of corpus callosum, cerebellar malformations, cataract.

Investigations:

• Detailed ultrasound examination, including neurosonography.
• Fetal brain MRI at ≥32 weeks’ gestation for the diagnosis of neuronal migration disorders.
• Fetal karyotyping: for diagnosis of Miller-Dieker syndrome (deletion 17p13.3).
• Parental karyotyping: to detect possible balance translocations involving 17p.

Follow up:

• Follow-up every 4 weeks.

Delivery:

• Standard obstetric care and delivery.

Prognosis:

• Life expectancy is about 10 years with severe neurodevelopmental delay.

Recurrence:

• Parental translocations: up to 25%.
• Isolated: no increased risk of recurrence.