- 1 in 300 births.
- Absence of the septum cavum pellucidum and tear-drop appearance of dilated posterior part of the lateral ventricles (‘tear drop’) in the standard transverse view of the brain at >18 weeks’ gestation.
- Complete or partial (usually of the posterior part) absence of the corpus callosum in a mid-sagittal view of the brain.
- Abnormal course of the pericallosal artery.
- The normal length of the corpus callosum at 20 weeks’ gestation is 18-20 mm.
- Chromosomal abnormalities (trisomies 8, 13 or 18, deletions and duplications) are found in 20% of cases.
- In about 50% of cases there is an association with any one of 200 genetic syndromes, defects in the central nervous system (mainly abnormal gyration, midline arachnoid cysts, Dandy-Walker complex and encephalocele) or defects in other systems (mainly cardiac, skeletal and genitourinary).
- Detailed ultrasound examination, including neurosonography.
- Invasive testing for karyotyping and array.
- TORCH test for fetal infections.
- Fetal brain MRI at ≥32 weeks for diagnosis of abnormalities that are not detectable by ultrasound, such as grey matter heterotopias, late sulcation and migration anomalies.
- Follow-up should be standard.
- Standard obstetric care and delivery.
- Isolated: neurodevelopmental delay in 30% of cases.
- Other defects: prognosis could be poor depending on the type of defect.
- Isolated: 3-5%.