The Society for Maternal-Fetal Medicine recently published a great review article about mild to moderate fetal ventriculomegaly. This is a condition that affects about 1 in every 1,000 babies. What causes Fetal Ventriculomegaly, how we evaluate it, how it’s treated, and how babies live after delivery is important.
Although considered somewhat rare, learning about this condition is important if your baby has just been diagnosed with Fetal Ventriculomegaly.
Our brains are made of wrinkles and folds of solid material, lots of nerve fibers, and some chambers that make and circulate fluid. It’s the fluid that we are talking about today. Cerebrospinal fluid (CSF) cushions the brain like a shock absorber, and carries nutrients to the brain and clears away waste products. The fluid is made in an area of the brain called the choroid plexus, inside chambers called ventricles.
CSF circulates out of the ventricles, around the brain and spinal cord, and back to the front of the brain, where it is reabsorbed. There is a balance between making fluid and reabsorbing fluid so that there is about the same amount of fluid in the head and spinal canal at any given time.
But what happens if the fluid can’t circulate normally? What if there is a blockage somewhere along the line?
Abnormal fluid circulation
Well, what happens is exactly what you would expect.
The fluid backs up, just like when a dam is built in a river. And the resulting condition is called ventriculomegaly, or hydrocephalus. The CSF collects in the ventricles of the brain and can’t circulate and be reabsorbed, so it builds up.
Sometimes, ventriculomegaly occurs not because of blockage of fluid, but because too much fluid is being produced. When we measure fetal heads, we measure the ventricles from side to side. Normally, they measure less than 10 mm from side to side. We usually categorize ventriculomegaly as mild (10-12 mm), moderate (13-15 mm), or severe (>15 mm).
Causes of ventriculomegaly
Why does ventriculomegaly happen? How is it evaluated? What kinds of problems can it cause for the baby? Is it treatable? What are outcomes like for babies affected by ventriculomegaly?
The Society for Maternal-Fetal Medicine recently published a great review article about mild to moderate ventriculomegaly, so let’s tackle these questions one by one.
- Normal variant – The ventricles are just a little wider than average. The majority of babies with mildly enlarged ventricles are simply normal if the ventricles aren’t getting bigger and there are no other abnormalities detected.
- Birth defects – If the brain is not forming normally, the ventricles may be enlarged.
- Infections – About 5% of mild to moderate ventriculomegaly is caused by infections. In particular, cytomegalovirus (CMV), toxoplasmosis, and Zika virus.
- Genetic disorders – Another 15-20% of cases of ventriculomegaly are caused by genetic and chromosome abnormalities. These are conditions like Down syndrome and various genetic syndromes. Genetic and chromosome abnormalities tend to be associated with more severe enlargement of the ventricles.
Evaluation of ventriculomegaly
- Detailed ultrasound – In up to half of cases, ventriculomegaly can be associated with other fetal abnormalities. So a thorough ultrasound is needed to look at fetal growth, anatomy, and signs of infection.
- Testing for abnormalities/infections – I’m not going to sugar coat this – amniocentesis is the best procedure for diagnosing both genetic disorders and infections because it can detect so many abnormalities. We have talked about noninvasive prenatal testing in a previous post. This is a great option for some screening, but it only looks for the few most common chromosome abnormalities. Amniocentesis can look at all chromosomes, plus a large number of genetic abnormalities. And we can look for viruses and infectious agents as well, more accurately than with blood work. If you decide that amniocentesis is not for you, we can use blood work to see if you may have been exposed to infections like CMV, toxoplasmosis, and Zika virus, and we can do noninvasive prenatal screening for the most common chromosome abnormalities.
- Magnetic resonance imaging (MRI) – MRI is becoming more useful in evaluating fetal brain and central nervous system abnormalities. So this can be a good way to see what is happening in the brain in more detail. MRI is considered safe during pregnancy because it does not involve radiation, BUT this should be done in a place where there are experienced providers to interpret the results. Not every fetus with ventriculomegaly needs a prenatal MRI.
How are pregnancies with ventriculomegaly managed?
If ventriculomegaly is more severe or progressive (>15 mm), you may be referred to see a pediatric neurosurgeon, because some babies may need treatment after delivery. Treatment typically consists of a ventriculoperitoneal (VP) shunt, where fluid can continuously drain from the ventricles into the abdominal cavity.
We usually perform serial ultrasounds to follow ventriculomegaly. As long as no other abnormalities are present, the pregnancy is managed exactly the same as any other pregnancy. Delivery happens at full term. Unless the head is becoming enlarged, we can usually wait for labor to start spontaneously.
What are outcomes like for babies with ventriculomegaly?
With isolated mild ventriculomegaly (this means 10-12 mm dilation and no other abnormalities), outcomes are well more than 90% of the time. That means normal neurodevelopment in more than 90% of these babies. That’s great news. This is most likely a normal baby.
With moderate ventriculomegaly (13-15 mm), the likelihood of normal neurologic development is 75-93%. Still pretty good. If there are other abnormalities, or if the ventriculomegaly worsens during the pregnancy, the outcome may not be as good.
For severe ventriculomegaly (>15 mm), long-term neurodevelopmental delays are likely. But remember, there is a lot of variation. Some babies who are treated do very well. And some babies who may have only mild ventriculomegaly but who have another type of birth defect may not do as well.
If you are told that your baby has ventriculomegaly, don’t panic. Consider testing for genetic abnormalities and infections. Gather as much information as you can, keep the conversation going with your OB and maternal-fetal providers, and do your best to stay positive!