- 1 in 100 fetuses at 20 weeks’ gestation.
- 1 in 1,000 births.
- 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).
- 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.
- 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.
- Ultrasound scans every 4 weeks to monitor the evolution of ventriculomegaly.
- Standard obstetric care and delivery.
- Cesarean section if the fetal head circumference is >40 cm.
- 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%.
- 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%.