What is hydrocephalus

Hydrocephalus is a condition where excess fluid builds up inside the skull, putting pressure on the brain. This can sometimes lead to brain damage, which can be fatal if left untreated.

The excess fluid is cerebrospinal fluid (CSF), a colourless liquid which surrounds the brain and the spinal cord. The normal job of CSF is to act as a ‘shock absorber’ to cushion the brain from bumps as the body moves. It also helps to make sure the brain gets the right amount of nutrients and oxygen, and helps clear waste.

Most CSF is produced inside spaces in the brain called ventricles. The CSF then drains out through thin channels into the space around the brain and spinal cord. CSF is then absorbed into the blood through small gaps in the arachnoid membrane, which covers the brain. If too much CSF is produced, or it can’t drain properly, then fluid can accumulate inside the ventricles in the brain. This causes the ventricles to expand, putting pressure on the brain.

This page has information about childhood hydrocephalus, its symptoms, causes, and treatments. We hope this page will be useful for parents and carers of children with hydrocephalus.

The information on this page may also be useful for health professionals such as GPs or health visitors, and education professionals such as teachers. 

Downloadable resources to help

Hydrocephalus is sometimes known as ‘water on the brain’. However, this term is outdated, as we now know that the fluid causing hydrocephalus is not water but CSF.

In the UK, hydrocephalus is pronounced “hi-droh-KEH-fa-lus”, and in the US it is pronounced “hi-droh-SEH-fa-lus”.


For many children, the cause of their hydrocephalus is unclear. However, known causes of hydrocephalus include:

Aqueduct stenosis

Between the spaces inside the brain (ventricles) there are small passageways which allow CSF to flow between them, one of which is called the cerebral aqueduct. But in some children, the aqueduct in their brain is too narrow, meaning that the flow of CSF slows down or is completely blocked. This means CSF cannot escape and causes the ventricle to swell, leading to hydrocephalus. This narrowing might not cause symptoms for many years after birth.

Spina bifida

This is a condition where the spine does not form properly as the baby develops. As well as causing problems in the spine, spina bifida can lead to changes in the structure of the brain. This means most babies born with spina bifida also have hydrocephalus.

Arachnoid cysts

Arachnoid cysts are fluid-filled sacs which form between the brain and a layer of tissue called the arachnoid membrane. As fluid accumulates inside the arachnoid cyst it grows, which can sometimes cause a blockage in the flow of CSF, causing hydrocephalus.


In very rare situations, genetic changes inherited from parents can lead to hydrocephalus. For example, a specific mutation in the X chromosome can cause hydrocephalus in boys, known as ‘X‑linked hydrocephalus’. Another genetic condition called Dandy-Walker syndrome can also cause hydrocephalus.

Bleeding inside the brain (haemorrhage)

Bleeds in the brain known as haemorrhages can cause blockages in the ventricles, or stop CSF from being re-absorbed, leading to hydrocephalus.

Premature birth

Hydrocephalus can sometimes develop in babies born prematurely before week 37 of pregnancy. This is thought to be caused by bleeding from the fragile blood vessels inside the brain.


Meningitis is when the membranes that cover the brain become inflamed because of an infection. This can lead to scarring of these membranes, which can restrict the flow of CSF and lead to hydrocephalus.

Brain tumours

Tumours can put pressure on the brain and block the flow of CSF, which can cause hydrocephalus.

What is the outlook for children with hydrocephalus?

The outlook for children with hydrocephalus varies considerably. Some children born with hydrocephalus will have permanent brain damage, while others will have very few problems in the long-term. If left untreated, however, the condition can be fatal.

The long-term effects of hydrocephalus will vary from child to child, and can be difficult to predict. Potential long-term complications of hydrocephalus include:

Not all children with hydrocephalus will experience these complications. You should speak to your child’s healthcare team to understand the potential outlook for them:

  • Learning disabilities
  • Problems with speech and memory
  • Short attention span
  • Vision problems, such as a squint or sight loss
  • Problems with physical coordination
  • Epilepsy



Hydrocephalus is usually treated with surgery. There are two types of surgery, and they both aim to reduce the build-up of CSF inside the brain.

A shunt is a thin tube which takes excess CSF from inside the brain or spine and transports it to somewhere else in the body.

The shunt system has a valve to make sure the CSF doesn’t drain away too quickly. Once the CSF drains to another part of the body it is re-absorbed into the blood.


There are different names for shunts, depending on where they are placed:

  • Ventriculo-peritoneal (VP) – takes CSF from the ventricles in the brain to the peritoneum (the abdomen)
  • Ventriculo-atrial (VA) – takes CSF from ventricles to the right atrium, one of the chambers of the heart
  • Ventriculo-pleural (VPL) – takes CSF from the ventricles to the pleural cavity, a fluid-filled sac which surrounds the lungs
  • Vision problems, such as a squint or sight loss
  • Lumbar-Peritoneal (LP) – takes CSF from the lower part of the spine (lumbar spine) to the peritoneum

The shunt is put in place during surgery under general anaesthetic. The tubes and the valve which make up the shunt system are placed underneath the skin.

Depending on the type of shunt used, shunts may need to be replaced (revised) as your child grows. Shunts may also need to be replaced if they become infected (see below for more information about shunt complications).

Endoscopic Third Ventriculostomy (ETV)

Some cases of hydrocephalus are caused by CSF building up inside a space in the brain called the third ventricle. To treat this, surgeons can make a small hole in the base of third ventricle in a procedure called an endoscopic third ventriculostomy (ETV). This hole allows CSF to drain out from the third ventricle and into the space surrounding the brain, where it is naturally absorbed into the blood. The surgeon uses a small camera called an endoscope to see where to make the hole.

ETV is only suitable for certain children with hydrocephalus. It might be effective for children who have aqueduct stenosis, spina bifida, or brain tumours which restrict the flow of CSF. Your child’s healthcare team will be able to tell you whether ETV is an option for them.

Complications of treatments

Complications can sometimes occur after surgery for hydrocephalus. You should speak to the team in charge of your child’s care to find out more about the possible complications from your child’s treatment.

Shunt Complications

The most common complication of shunts is blockage. This will cause excess cerebrospinal fluid (CSF) to build up inside the brain, leading to symptoms of hydrocephalus, including (but not limited to):

  • Unusually large head or rapid head growth (in infants)
  • Bulging/tense fontanelle (soft spot) in infants
  • Noticeable changes in scalp vains
  • Sleepiness
  • Poor feeding
  • Headaches
  • Nausea and vomiting
  • Irritability
  • Problems with movement, balance or coordination
  • Vision changes
  • Eyes that are fixed looking downwards (“sunsetting”)
  • Changes in personality, behaviour or school performance
  • Developmental delays or regression of skills
  • Seizures
  • Feeling that a child is ‘just not quite right’

Another complication of shunt insertion is infection. Infections are most likely to happen within a few months of the shunt being installed.

Symptoms of shunt infection

  • High temperature (38°C or more)
  • Redness and tenderness along the length of the shunt
  • Abdominal (tummy) pain, in the case of VP shunts
  • Neck stiffness
  • Redness or swelling of the incision site

If your child develops a shunt complication such as a blockage or infection, surgery will be needed to replace part/all of shunt and prevent brain damage. Shunt infections will also require treatment with antibiotics.

If your child experiences any symptoms of shunt infections or failure, you should contact your child’s healthcare team immediately.

It is estimated that around 4 in 10 shunts will fail within the first year after surgery, and around 7 out of 10 will need replacing within 10 years.

Endoscopic Third Ventriculostomy (ETV) complications

Infections are still possible after an ETV, but they are less likely to happen than with a shunt.

Another possible complication of ETV is that the hole created during surgery might close, causing fluid to build up inside the brain again.

Symptoms of ETV complications are similar to the initial symptoms of hydrocephalus. As before, these symptoms depend on the age of the child, but can include:

Where to find more information

You can speak to the healthcare team looking after your child to find out more information about any aspect of hydrocephalus.

More information about hydrocephalus can be found on our signposting page

There are also several hydrocephalus support groups on Facebook for parents and carers. These groups are run by families of children with the condition, and are independent from Harry’s HAT – we are not responsible for the content or information in these groups.