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What causes hydrocephalus?

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Why focus on hydrocephalus?

There are many reasons that hydrocephalus might occur. Often it is secondary to another condition that has affected the brain or the central nervous system. Many of these conditions have their own symptoms and complications that can have an effect on someone’s life. Some of these effects may be physical but some conditions can also have an impact on how the brain works. They too can change the way a person thinks and acts (behaves) even when hydrocephalus does not occur.

Hydrocephalus is however an ongoing, lifelong condition. It can continue to make it difficult for the brain to work properly which is why this site has focused on hydrocephalus in particular. Many of the issues discussed and the solutions provided could be helpful to any child or young person experiencing the difficulties described in the Living with Hydrocephalus section.

Everyday difficulties can be caused by how hydrocephalus changes the way the brain works. You can read more about how changes in the brain affect the way it processes information by looking at the Hydrocephalus and the brain section.

The following sub-sections look at conditions that can cause hydrocephalus.

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Congenital Hydrocephalus

This means hydrocephalus is present at birth. It is important to remember that this term does not imply that it is hereditary. The exact cause of congenital Hydrocephalus is not always known. Many of the conditions described here will occur before or shortly after birth.

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Spina Bifida

Spina bifida happens before birth, when the bones in the spine do not form properly. This can leave the spinal cord unprotected and sometimes it pushes through the gaps left in the spinal bones. This condition can cause a variety of issues for young people and their families. You can read more about spina bifida on Spina Bifida Hydrocephalus Scotland's (SBH Scotland) main website.

Most babies born with spina bifida also have Hydrocephalus. This is because, as well as problems with the spinal cord, certain parts of the brain do not develop the way they should before birth. This prevents proper drainage of the CSF which causes a collection of fluid and increased pressure in the brain. This can compress the abnormal parts of the brain (the bits affected by spina bifida) even further.

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Babies born prematurely are at risk of developing Hydrocephalus. When a baby is born early, its brain is still developing at the time of birth. This makes it far more vulnerable than the brain of a baby that goes to full term.

The area which lies just beneath the lining of the cavities (ventricles) in the brain has a plentiful blood supply. Its blood vessels are very fragile and can easily burst if the baby suffers too large a swing in blood pressure or in the amount of fluid in the system.

If these complications do occur, then the baby is at risk of developing a haemorrhage from rupture of the fragile vessels. This can lead to a blood clot developing, which in some cases is big enough to break through the wall of the ventricle. If the clot blocks the flow of CSF, the baby will develop Hydrocephalus. Even if a blood clot does not develop, the blood cells from the haemorrhage can cause blockage. The blockage may be temporary or permanent.

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Brain haemorrhage

Other forms of brain haemorrhage, including those occurring in adults ('stroke') can cause blockages to the flow of CSF. This might result in post-haemorrhagic Hydrocephalus.

Damage to the brain, caused by a haemorrhage in either infancy or adulthood, may have an impact on the type and severity of difficulty experienced by someone with hydrocephalus.

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This is an infection of the membranes covering the brain. The inflammation and debris from this infection may block the drainage pathways of CSF and could result in Hydrocephalus. Meningitis can occur at any age, but it is more common in children. The incidence of one form, haemophilus meningitis, has been drastically reduced by HIB vaccine.

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Dandy-Walker cysts

There is a particular group of disorders involving the formation of fluid-filled cysts in the CSF system (for example, Dandy-Walker cysts). In these cases, Hydrocephalus is often due to pressure on the surrounding tissues by the enlarging cyst.

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Tumours can be benign or malignant. Tumours of the brain cause compression and swelling of surrounding tissues resulting in poor drainage of CSF. In the treatment of brain tumours it is often necessary to control Hydrocephalus, which might only be temporary.

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Genetic and other causes

In very rare circumstances, Hydrocephalus is due to hereditary factors which might affect future generations. There are many other very rare causes of hydrocephalus, and sometimes it is unknown why it has happened.

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Cerebral palsy

Cerebral palsy is not a cause of hydrocephalus but may occur alongside it. Cerebral palsy can also be associated with brain trauma before or after birth from a haemorrhage or meningitis, for example. Co-occurrence of hydrocephalus and cerebral palsy can increase the type and severity of difficulties experienced.

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