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Ventriculomegaly is a condition in which the lateral ventricles (fluid-filled spaces in the brain) are larger than normal. It's usually due to a buildup of cerebrospinal fluid (CSF), the clear liquid surrounding the brain and spinal cord that cushions them from injury. Only one or both lateral ventricles may be affected. Most often, treatment is required only if the accumulation of CSF is causing hydrocephalus, pressure on the brain. Ventriculomegaly is the most common fetal brain abnormality, occurring in up to 1.5 in 1,000 pregnancies.

Causes of ventriculomegaly

This condition typically occurs early in pregnancy and happens spontaneously, meaning it's not inherited. Why a fetus develops ventriculomegaly is not always clear, but four main events can cause the ventricles to expand:

  • A blockage that prevents CSF from circulating and being absorbed normally in the brain
  • A minor imbalance in CSF circulation and absorption
  • Defects in brain development
  • Damage or loss of brain tissue

Possible outcomes

The outcome for a fetus with ventriculomegaly depends on several factors, including the size of the enlarged ventricles, whether the problem is getting worse, and whether there are other developmental or genetic abnormalities. Severe, progressive cases can lead to neurological disabilities. If the ventricles are only mildly enlarged (10 to 15 mm in size) and not getting bigger, and no brain damage or other abnormalities are found, there are usually no long-term consequences. In many fetuses, especially those with borderline ventriculomegaly, the condition resolves on its own, with no ill effects. What's more, with timely treatment, even infants with hydrocephalus who haven't suffered brain damage have an excellent prognosis for normal development.

The UCSF Fetal Treatment Center is a world leader in diagnosing and treating prenatal conditions, including ventriculomegaly. In 1981, we performed the first successful open fetal surgery ("open" is the traditional approach in which the surgeon works through a large incision), and we have more experience with both open and minimally invasive fetal surgery than any institution in the world. Our team includes fetal and pediatric surgeons, radiologists, perinatologists, neonatologists, cardiologists, urologists, geneticists, anesthesiologists, pediatric neurologists, pediatric neurosurgeons, nurses and social workers. These experts work closely together to ensure our patients receive care that meets all of their needs.

Our researchers are currently investigating whether the results of a fetal MRI can indicate the likelihood of disability and what families may expect for their child's health and development. This information will help parents make decisions during pregnancy and prepare for challenges their child and family may face.

Contact us

To request an appointment, call the Fetal Treatment Center.

Signs and symptoms

When a fetus is affected with ventriculomegaly, the pregnant person doesn't experience symptoms. However, measuring the ventricles is a standard part of the prenatal ultrasound screening done in the second trimester. Usually, when ventriculomegaly is first detected, the ventricles are wider than 10 mm. The ventricles are monitored throughout the remainder of the pregnancy, watching for any changes in the ventricle size.


If a prenatal ultrasound shows enlarged ventricles, your doctor may recommend additional tests to determine the cause and check for associated problems. These tests may include:

  • Amniocentesis – We take a sample of the fluid surrounding the fetus to analyze the baby's DNA and detect genetic abnormalities.
  • Fetal MRI – This imaging technique uses a strong magnetic field and radio waves to produce detailed images, potentially revealing problems that don't appear on ultrasound.
  • Level II ultrasound (fetal survey) – This scan provides more detailed images of the fetus than did the earlier (level I) prenatal ultrasound.


During pregnancy, the only treatment is to monitor the condition of the fetus and whether the ventricles get bigger. After birth, treatment is needed only if hydrocephalus develops. This fluid buildup usually happens slowly, over the course of weeks. In most cases, we know by six months whether your baby needs treatment.

The main way to relieve the pressure of excess CSF is via a ventriculoperitoneal shunt. This is a small, plastic tube that's implanted in the brain and threaded under the skin to the abdomen; it allows the excess CSF to drain into the abdominal cavity, where it can be absorbed by the body. A pediatric neurosurgeon will place the shunt in a procedure for which your child will be under general anesthesia (completely asleep). Regular follow-ups will be needed to make sure the shunt is functioning properly, but it shouldn't interfere with your child's ability to live a normal, healthy life.

UCSF Benioff Children's Hospitals medical specialists have reviewed this information. It is for educational purposes only and is not intended to replace the advice of your child's doctor or other health care provider. We encourage you to discuss any questions or concerns you may have with your child's provider.

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