Merck Manual

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Last full review/revision Apr 2019| Content last modified Apr 2019
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What is hydrocephalus?

"Hydro-" means water, and "-cephalus" refers to the head. Hydrocephalus is too much water inside the head. It's sometimes called "water on the brain."

Your brain has several hollow spaces inside it that are filled with fluid. In hydrocephalus, there is too much fluid in these spaces.

  • Extra fluid in the brain can make your baby's head bigger

  • If pressure builds up too high in the brain, your baby can have developmental problems

  • Fluid may build up because of a birth defect, bleeding within the brain, or a brain tumor

  • Doctors do procedures to drain the extra fluid

What causes hydrocephalus?

A baby's skull is made of several different bones. For the first couple of years, these bones are only loosely connected. Later, the bones grow together into one solid bone. But before the bones grow together, increased fluid pressure inside the brain can make the bones spread apart. This keeps the pressure from getting dangerously high, but it makes the baby's head bigger. The skull of older children and adults can't expand, so increased pressure damages the brain and can be rapidly fatal.

The following can cause extra fluid in the brain:

Babies can be born with hydrocephalus, or it can happen after birth.

What are the symptoms of hydrocephalus?

The symptoms of hydrocephalus depend on where and how much fluid there is. A baby with hydrocephalus may:

  • Have an abnormally large head

  • Be fussy or show little interest in anything

  • Develop a high-pitched cry

  • Forcefully throw up

  • Have seizures

  • Have bulges in the soft spots of the skull

  • Have one eye that looks in a different direction than the other eye (cross-eyed)

Older children may have a headache, vision problems, or both.

If not treated, children with hydrocephalus can have learning disabilities or lose vision.

How can doctors tell if my baby has hydrocephalus?

Doctors do routine tests before and after a baby is born to test for hydrocephalus:

  • Before birth, doctors will do an ultrasound and measure the baby's head size

  • After a baby is born, doctors measure the head size with a tape measure and if it's large, they may do CT scan, MRI, or ultrasound of the head

How do doctors treat hydrocephalus?

Doctors treat hydrocephalus in different ways depending on what's causing it, how much fluid there is, and if it’s getting worse.

If there's not much extra fluid and it's not getting worse, your baby may not need treatment.

To temporarily help relieve symptoms, doctors may:

  • Take fluid out with a needle put into the brain or sometimes the lower back (spinal tap)

If there's a lot of fluid or the fluid is causing symptoms, doctors may:

  • Put in a thin plastic tube called a shunt in the baby's brain to drain the fluid

  • Do brain surgery to correct a problem that caused fluid to build up

With a shunt, one end of the plastic tube is in the fluid-filled space in the brain. The tube goes under the baby's skin and the other end is inside the belly. This creates a path for fluid to drain from the brain.

Shunts are usually permanent, but sometimes doctors can remove them as the child grows older.

A shunt can get clogged up, break, or get infected. If so, the shunt may have to be replaced.

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