Prevalence:

• 1 in 100 fetuses at 20 weeks’ gestation.
• 1 in 1,000 births.

Ultrasound diagnosis:

• Bilateral or unilateral dilation of the lateral cerebral ventricles observed in the standard transverse section of the brain.
• Subdivided according to the diameter of the lateral ventricle into mild (10-12 mm), moderate (13-15 mm) and severe (>15 mm).

Associated abnormalities:

• Chromosomal defects, mainly trisomies 21, 18 or 13, are found in 10% of cases. In isolated ventriculomegaly there is a 4-fold increase in risk for trisomy 21. The risk is inversely related to the severity of ventriculomegaly.
• Cerebral and non-cerebral defects and genetic syndromes are found in 50% of cases.

Investigations:

• Detailed ultrasound examination, including neurosonography.
• Invasive testing for karyotyping and array.
• TORCH test for fetal infections.
• Maternal blood testing for antiplatelet antibodies in cases with evidence of brain hemorrhage.
• Fetal brain MRI at ≥32 weeks for diagnosis of abnormalities of neuronal migration, such as lissencephaly.

Follow up:

• Ultrasound scans every 4 weeks to monitor the evolution of ventriculomegaly.

Delivery:

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

Prognosis:

• Isolated mild / moderate: neurodevelopmental delay in 10% of cases, this may not be higher than in the general population.
• Isolated severe: 10 year survival 60%, severe mental handicap 50%.

Recurrence:

• Isolated <1%. Increases to 5% if there is a history of affected fetus or sibling.
• Part of infection: no increased risk.
• Part of trisomies: 1%.
• X-linked hydrocephaly: 50% of males.
• Associated with alloimmune thrombocytopenia and no treatment: 100%.