Ventriculomegaly

The ventricles are responsible for the production and circulation of cerebrospinal fluid (CSF). When the ventricles are enlarged, it is not necessarily because there is 'too much pressure' (which is hydrocephalus), but rather a sign that the brain's anatomy needs a closer look.

We categorize the severity as follows:

• Mild (10 to 12 mm): The most common form. If isolated (no other issues), the vast majority of these babies have normal development.
• Moderate (12 to 15 mm): Requires more frequent monitoring and sometimes further testing like fetal MRI.
• Severe (Above 15 mm): Often called hydrocephalus if the pressure is high. This is more likely to be associated with other brain abnormalities and carries a more guarded prognosis.

Ventriculomegaly is diagnosed in about 1 in 100 to 1,000 pregnancies.

Risk factors or potential causes that we investigate include:

• Genetic Variations: Chromosomal conditions such as Down syndrome or single-gene disorders.
• Brain Structure: Issues with how the brain formed (e.g., Agenesis of the Corpus Callosum).
• Infections: 'TORCH' infections, particularly CMV (Cytomegalovirus) or Toxoplasmosis, which can affect brain development.
• Haemorrhage: Rare incidents where a small bleed in the fetal brain causes blockage of fluid flow.

At the MFM Unit, the diagnostic journey for ventriculomegaly is comprehensive:

1. Advanced Neurosonography: A deep-dive ultrasound of the brain, looking at the cerebellum, the corpus callosum, and the midline structures.
2. Infection Screening: Blood tests for the mother to rule out recent viral infections (CMV, Toxoplasmosis).
3. Genetic Testing: We often discuss Amniocentesis with Chromosomal Microarray (CMA) to ensure no underlying genetic cause is missed.
4. Fetal MRI: In some moderate or severe cases, we may refer you for a specialized fetal brain MRI (usually after 24-26 weeks) to get the clearest possible view of the brain surface (the cortex).

Management focuses on serial monitoring to see if the fluid is stable, decreasing, or increasing.

• Stability: If the fluid remains stable and no other issues are found, the focus is on a normal delivery at term.
• Progression: If the ventricles grow rapidly, it may indicate a blockage that needs to be addressed after birth by a pediatric neurosurgeon.
• Delivery: Most babies with ventriculomegaly can be delivered vaginally. A Caesarean section is only required if the baby's head becomes significantly larger than average, which is rare in mild/moderate cases.

The outcome depends entirely on *why* the ventricles are large.

• Isolated Mild Ventriculomegaly: Over 90% of children have normal neurological development and reach their full potential.
• Associated Findings: If there are other structural or genetic issues, the prognosis depends on the specific condition found.
• Severe Ventriculomegaly: These babies require follow-up with pediatric neurosurgeons after birth. Some may need a small 'shunt' (tube) placed to drain the excess fluid, though many do well with early intervention.

If your doctor has mentioned 'fluid in the brain' or a measurement 'just at the limit' (e.g., 10 or 11 mm), you should be seen by a subspecialist at the MFM Unit.

The expertise required to perform a detailed fetal brain scan is specialized. Our consultants, including Dr. Leanne Bricker, provide the expert neuro-imaging and the evidence-based counseling needed to guide you through the next steps and provide reassurance where it is appropriate.