- 1 in 100,000 births.
- 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”.
- 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.
- 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 every 4 weeks.
- Standard obstetric care and delivery.
- Life expectancy is about 10 years with severe neurodevelopmental delay.
- Parental translocations: up to 25%.
- Isolated: no increased risk of recurrence.