Prevalence:

• 1 in 300 births.

Ultrasound diagnosis:

• 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.

Associated abnormalities:

• 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).

Investigations:

• 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:

• Follow-up should be standard.

Delivery:

• Standard obstetric care and delivery.

Prognosis:

• Isolated: neurodevelopmental delay in 30% of cases.
• Other defects: prognosis could be poor depending on the type of defect.

Recurrence:

• Isolated: 3-5%.