Hydrocephalus is a build-up of fluid on the brain. The excess fluid puts pressure on the brain, which can damage it.

The damage to the brain can cause a wide range of symptoms, including:


being sick

blurred vision

difficulty walking

Hydrocephalus can usually be treated using a piece of equipment known as a shunt. This is a thin tube that's surgically implanted in the brain and drains away the excess fluid. If left untreated, hydrocephalus can be fatal.

What causes hydrocephalus?

In the past, hydrocephalus was often referred to as "water on the brain". However, the brain isn't surrounded by water but by a special fluid called cerebrospinal fluid (CSF).

CSF has three important functions, it:

protects the brain from damage

removes waste products from the brain

provides the brain with the nutrients it needs to function properly

The brain constantly produces new CSF (about a pint a day), while old fluid is released from the brain and absorbed into the blood vessels. However, if this process is interrupted, the level of CSF can quickly build-up, placing pressure on the brain.

Types of hydrocephalus

There are three main types of hydrocephalus:

hydrocephalus that's present at birth (congenital hydrocephalus)

hydrocephalus that develops after birth (acquired hydrocephalus)

hydrocephalus that usually only develops in older people (normal pressure hydrocephalus or NPH)

These are described below.

Congenital hydrocephalus

Congenital hydrocephalus is present in babies when they're born and can be caused by birth defects, such as spina bifida, or as a result of an infection the mother develops during pregnancy, such as mumps orrubella (German measles).

It's estimated that spina bifida affects one baby in every 1,000 born in Britain. Most of them will have hydrocephalus.

Congenital hydrocephalus carries the risk of long-term mental and physical disabilities as a result of permanent brain damage.


Acquired hydrocephalus

Acquired hydrocephalus can affect children or adults. It usually develops after an illness or injury. For example, it may occur after aserious head injury, or as a complication of a medical condition, such as a brain tumour.

Normal pressure hydrocephalus

Normal pressure hydrocephalus (NPH) is an uncommon and poorly understood condition that most often affects people over 60 years of age. It can sometimes develop after an injury or a stroke, but in most cases the cause is unknown.

Mobility problems, dementia and urinary incontinence are the main symptoms of NPH, but because they're similar to the symptoms of the other conditions, NPH can be difficult to diagnose.

Symptoms of hydrocephalus 

Hydrocephalus (fluid on the brain) causes slightly different symptoms depending on the type of hydrocephalus and the age of the person affected.

Congenital hydrocephalus

Babies born with hydrocephalus (congenital) often have distinctive physical characteristics. Physical signs in a baby include:

an unusually large head 

their scalp may be thin and shiny with easily visible veins

a bulging or tense fontanelle (the soft spot on the top of their head) 

their eyes may appear to be looking down; this is known as the ‘setting-sun sign’ because the eyes resemble the sun setting below the horizon

the muscles in your baby’s lower limbs may appear stiff and be prone to muscle spasms

As well as these physical signs, congenital hydrocephalus can also cause symptoms such as:

poor feeding


being sick


Acquired hydrocephalus

Hydrocephalus that develops in adults or children (acquired) can causeheadaches. The headache may be worse in the morning after waking up because the fluid in your brain doesn't drain so well while you're lying down and may have built up overnight. Sitting up for a while may improve your headache. However, as the condition progresses, the headaches may become continuous. 

Other symptoms of acquired hydrocephalus include:

neck pain

feeling sick

being sick (which may be worse in the morning)

drowsiness, which can progress to a coma

changes in your mental state, such as confusion

blurred vision or double vision

difficulty walking

not being able to control your bladder (urinary incontinence) and, in some cases, your bowel (bowel incontinence)

Normal pressure hydrocephalus

Unlike the other two types of hydrocephalus, the symptoms of hydrocephalus that develop in older people (normal pressure hydrocephalus or NPH) usually develop slowly, over the course of many months or years.

NPH has three sets of distinctive symptoms. It affects your:

mobility (how you walk)

urinary system

mental abilities

These are discussed below.

How you walk 

The first noticeable symptom of NPH is a change in how you walk (your gait). You may find it increasingly difficult to take the first step when you want to start walking. Some people have described it as feeling as though they're frozen to the spot. You may also shuffle rather than take proper steps.

As the condition progresses, you may become increasingly unsteady on your feet and be more likely to fall, particularly when turning.

Urinary symptoms

The change in the way that you walk is often followed by bouts of urinary incontinence, which may include symptoms such as:

a frequent need to urinate

an urgent need to urinate

loss of bladder control

Mental abilities

The normal thinking process also starts to slow down. This can take the form of:

being slow to respond to questions

reacting slowly to situations

being slow to process information

These symptoms may indicate that you have mild dementia. They should start to improve when NPH is treated.

Causes of hydrocephalus 

The causes of hydrocephalus are poorly understood.

It's thought that congenital hydrocephalus may be the result of a brain defect restricting the flow of cerebrospinal fluid.

Acquired hydrocephalus is often caused by an illness or injury that affects the brain.

Normal pressure hydrocephalus (NPH) may also be the result of an infection, illness or injury, but in many cases it's not known why the condition occurs.

Cerebrospinal fluid

Cerebrospinal fluid (CSF) is created in the brain. It flows around the brain through a series of passageways called ventricles.

Excess CSF moves out of the brain, where it's absorbed back into the bloodstream by a specialised tissue called the arachnoid villi. The arachnoid villi act like a one-way valve, allowing excess CSF to leave the brain and filter into blood vessels while preventing the blood from leaking into the brain and damaging it.

Hydrocephalus can develop if:

there's a blockage in one of the ventricles so that excess fluid can't move out of the brain

there's a problem with the arachnoid villi so that fluid is unable to filter into the blood vessels

the brain starts to produce too much CSF (this is very rare)

Congenital hydrocephalus

Congenital hydrocephalus (when a baby is born with the condition) may be the result of a defect in the development of the brain that restricts the flow of CSF. This can be caused by certain health conditions, such as spina bifida.

Congenital hydrocephalus can also occur in babies born prematurely (before week 37 of the pregnancy). Some premature babies have bleeding in the brain, which can block the flow of CSF and cause hydrocephalus.

Other possible causes of congenital hydrocephalus include:

X-linked hydrocephalus – caused by a mutation (change in the genetic material) of the X chromosome

rare genetic disorders – such as Dandy Walker malformation

arachnoid cysts – fluid filled sacs located between the brain or spinal cord and the arachnoid membrane (one of the three membranes surrounding the brain and spinal cord)

In many cases of congenital hydrocephalus, the cause is unknown. This is known as idiopathic.

Acquired hydrocephalus

Hydrocephalus that develops in adults or children (acquired hydrocephalus) is usually the result of an injury or illness that causes a blockage in the ventricles of the brain.

Possible causes of acquired hydrocephalus include:

bleeding inside the brain – for example, if blood leaks over the surface of the brain (subarachnoid haemorrhage)

blood clots in the brain (venous thrombosis)

meningitis – an infection of the membranes surrounding the brain and spinal cord

brain tumours

head injury


Some people are born with narrowed passageways in their brain that restrict the flow of cerebrospinal fluid, but don't cause any symptoms until years later. 

Normal pressure hydrocephalus

Hydrocephalus that develops in older people (normal pressure hydrocephalus or NPH) can occur after a brain injury, bleeding in the brain or an infection. However, in most cases, there's no clear reason.

There are several theories to explain what happens to the brain in cases of NPH. Some are outlined below.

Problems with the arachnoid villi

It's thought that NPH occurs when something goes wrong with the arachnoid villi (the tissue that allows CSF to filter into the blood vessels). If the blood vessels don't reabsorb the fluid it will gradually increase pressure, leading to brain damage.

Underlying health conditions

NPH may be caused by conditions that affect the normal flow of blood. For example, diabetes, heart disease, or having a high level of cholesterol in the blood.

The exact cause is unknown, but conditions that affect the blood vessels within the brain, or those that supply blood to the brain (cerebrovascular disease), may be linked to NPH.

Diagnosing hydrocephalus 

Brain scans are used to diagnose hydrocephalus (fluid on the brain).

Congenital hydrocephalus

In some cases, an ultrasound scan can be used to detect congenital hydrocephalus before a baby is born. An ultrasound scan uses sound waves to create an image of your womb and the baby inside.

If your baby has physical characteristics of congenital hydrocephalus after they're born, such as an enlarged head, they may be referred for an ultrasound scan. They may also need a computerised tomography (CT) scan or a magnetic resonance imaging (MRI) scan.

These can be used to examine the brain in greater detail. They can show the build-up of fluid on the brain and the increased pressure, as well as highlighting any structural defects that may be causing the hydrocephalus. 

Acquired hydrocephalus

Hydrocephalus that develops in adults or children (acquired hydrocephalus) can be diagnosed using a combination of CT and MRI scans. The scans can also reveal possible causes of your symptoms, such as a brain tumour.

Normal pressure hydrocephalus

Normal pressure hydrocephalus (NPH) usually develops in older people and can be difficult to diagnose. This is because the symptoms come on gradually and are similar to those of more common conditions, such as Alzheimer's disease.

It's important to make a correct diagnosis because, unlike Alzheimer’s disease, it's possible to relieve the symptoms of NPH with treatment.

A diagnostic checklist will be used to examine:

how you walk (your gait)

your mental ability

symptoms that affect your bladder control, such as urinary incontinence

the appearance of your brain during CT, MRI and ultrasound scans

You may be diagnosed with NPH if you have an impaired gait, slowing of the normal mental processes and urinary incontinence, and scans have shown that your cerebrospinal fluid (CSF) is at a higher level than usual. However, you may not have all of the symptoms on the above checklist.

Further tests may also be carried out to decide whether you would benefit from having surgery such as:

a lumbar puncture

a lumbar drainage test

a lumbar infusion test

These procedures are described below.

Lumbar puncture

A lumbar puncture, also known as a spinal tap, is a procedure used to take a sample of CSF from your lower back.

A small amount of fluid is removed from the area between your back bones (vertebrae). The pressure of the CSF sample can then be checked.

Removing some CSF during a lumbar puncture may help improve your symptoms. If this is the case, it's a good indication that you may benefit from treatment with surgery (see treating hydrocephalus).

Lumbar drain

You may have a lumbar drain if a lumbar puncture doesn't improve your symptoms.

A tube is inserted between your back bones to drain a large amount of CSF. This is carried out over a few days to see if your symptoms improve. The procedure is usually carried out under local anaesthetic.

Lumbar infusion test

A lumbar infusion test involves slowly injecting fluid into your lower back while measuring the pressure. The additional fluid should be absorbed by your body so the pressure stays low. However, if your body can't absorb the extra fluid, the pressure will rise which could indicate NPH and that surgery will be beneficial. 

Treating hydrocephalus 

Hydrocephalus (fluid on the brain) is treated with surgery.

Congenital and acquired hydrocephalus

Babies born with hydrocephalus (congenital) and adults or children who develop hydrocephalus (acquired) usually need prompt treatment to reduce the pressure on their brain. If hydrocephalus isn't treated, the increase in pressure will cause brain damage.

Both congenital and acquired hydrocephalus will be treated with either shunt surgery or neuroendoscopy (see below).

Normal pressure hydrocephalus

Normal pressure hydrocephalus (NPH) can sometimes be treated with a shunt, although experience has shown that not everyone with the condition will benefit from shunt surgery.

Due to the risk of complications, you'll need tests to assess whether the potential benefits of surgery outweigh the risks. A lumbar drainage or lumbar infusion test, or both, can be used to determine whether shunt surgery will benefit you.

Shunt surgery

Shunt surgery involves implanting a thin tube, called a shunt, in the brain. The excess cerebrospinal fluid (CSF) in the brain runs through the shunt to another part of the body, usually the abdomen. From here, the fluid is absorbed into your blood stream. The shunt has a valve inside to control the flow of CSF and ensure it doesn't drain too quickly. You can feel the valve as a lump under the skin of your scalp.

The operation

Shunt surgery is carried out by a neurosurgeon (a specialist in brain and nervous system surgery). It's carried out under general anaestheticbefore the operation and usually takes one to two hours. 

After the operation, you may need to spend a few days in hospital to recover. If you have stitches, they may dissolve or they may need to be removed. Some surgeons use skin staples to close the wound which will need to be removed after a few days.

After the shunt has been installed, further treatment for hydrocephalus may be needed if it becomes blocked or infected. Shunt repair surgerywill then be necessary.

Endoscopic third ventriculostomy (ETV)

An alternative procedure to shunt surgery is an endoscopic third ventriculostomy (ETV).

Instead of inserting a shunt, ETV involves making a hole in the floor of the brain to allow the trapped CSF to escape to the surface of the brain where it can be absorbed.

An ETV isn't suitable for everyone. However, it could be an option if the build-up of CSF in your brain is due to a blockage (obstructive hydrocephalus). The CSF will be able to drain through the hole, avoiding the blockage.

The operation

An ETV is carried out under general anaesthetic. The neurosurgeon makes a small hole in your skull and uses an endoscope to look inside the chambers of your brain. An endoscope is a thin, long tube with a light and video camera at one end.

A small hole is made inside your brain with the help of the endoscope. After the endoscope has been removed, the wound is closed using stitches. The procedure takes around one hour.

There's less risk of infection after an ETV than with shunt surgery. However, as with all surgical procedures, there are some risks associated with ventriculostomy.

The long-term results for treatment with ETV are similar to those for a shunt operation. As with shunts, ETVs may become blocked months or years after surgery and the symptoms will return.

Complications of hydrocephalus 

Hydrocephalus (fluid on the brain) can cause complications, or complications may develop as a result of having surgery to treat it.

Shunt malfunction

A shunt is a delicate piece of equipment prone to malfunction, usually through blockage or infection. It's estimated that up to four out of 10 shunts will malfunction in the first year after surgery. Sometimes, a scan after the operation shows the shunt isn't in the best position, and that further surgery may be needed to reposition it.

If a baby or child has a shunt fitted, the shunt may become too small as your child grows, and it will need to be replaced. As most people need a shunt for the rest of their life, more than one replacement may be needed.

It's estimated that most children with hydrocephalus may have an average of two procedures for shunt problems before they're 10 years old.

Occasionally, bleeding can occur when shunt tubes are positioned. This can result in nerve problems, such as weakness down one side. There's also a small risk of fits following any type of brain surgery.

In younger children, particularly babies, cerebrospinal fluid (CSF) can run alongside the shunt rather than down it, and it can leak through the skin wound. If this occurs, further stitches will be needed to stop the leak.

Shunt blockage

A shunt blockage can be very serious because it can lead to an excess build-up of fluid on the brain, which can cause brain damage. This will cause the symptoms of hydrocephalus. Emergency surgery will be required to replace the malfunctioning shunt.

Shunt infection

Shunt infection is also a relatively common complication. The risk of infection can be around 3-15% and is more likely to occur during the first few months after surgery.

The symptoms of a shunt infection may include:

redness and tenderness along the line of the shunt

a high temperature (fever) of 38C (100.4F) or above


being sick

neck stiffness

tummy pain (if the shunt drains into your tummy)

irritability or drowsiness in babies

Contact your care team immediately if you or your child has these symptoms. You may need a course of antibiotics to treat the infection and, in some cases, surgery may be required to replace the shunt.

Complications of endoscopic third ventriculostomy (ETV)

An endoscopic third ventriculostomy (ETV) is a surgical procedure to create a small hole in the floor of your brain. Complications can occur after this type of operation, such as:

the hole can close

your brain may not be able to absorb the cerebrospinal fluid that's now draining through it

you may develop an infection, although this is less likely than after shunt surgery

you may have bleeding inside your brain (this is usually minor)

If there's a problem with the hole, it may be possible to repeat the procedure, or you may need to have a shunt fitted (see treating hydrocephalus).

Other risks of ETV include nerve problems, such as weakness down one side of the body, double vision or hormone imbalances. Most nerve problems will get better, but there's a small risk of permanent problems. There's also a small risk of epilepsy, and a very small risk of an injury to one of the blood vessels in the brain, which may be fatal.

Long-term complications of congenital hydrocephalus

Many babies born with hydrocephalus (congenital hydrocephalus) have permanent brain damage. This can cause a number of long-term complications such as:

learning disabilities

impaired speech

memory problems

short attention span

problems with organisational skills

vision problems, such as a squint and visual impairment

problems with physical co-ordination



Shunt alert cards

Shine, the hydrocephalus and spina bifida charity, has produced a series of ‘shunt alert cards’ for adults and children. You carry the card with you if you've had a shunt fitted.

They're useful in a medical emergency if you have symptoms of a blockage or infection. The healthcare professionals treating you will be aware that you have a shunt fitted. They'll check whether this is causing your symptoms. 

To apply for a shunt alert card, you can either fill out a form on the Shine website or call 01733 555988.