Hydrocephalus can be congenital (you are born with it) or acquired (occurring at any point in your lifetime).
This means that hydrocephalus is present at birth. It is important to remember that this term does not imply that it is hereditary. Often the exact cause of congenital hydrocephalus cannot be determined but known causes can include:
In some people, from the early days of developing in the womb, one of the pathways (aqueduct) linking the ventricles in the brain is narrowed (stenosis) and either blocks completely or is too narrow to let enough CSF pass through, this results in increased CSF pressure. Although this always happens before birth, a slight narrowing may mean symptoms do not develop for many years.
If the blockage is complete or significant, a baby’s hydrocephalus may be detected at the midterm scan, but signs can develop at any time in the pregnancy.
In very rare circumstances, hydrocephalus is due to hereditary factors, which may affect future generations, such as X-linked hydrocephalus. This condition, only affects boys, but girls have a chance of passing the gene to their children. Around half of baby boys born to mothers who carry the X linked gene develop the condition. X linked hydrocephalus is associated with severe learning impairment, movement difficulties and adducted thumbs (which are held against the palm).
These include group B streptococcus which can cause neonatal meningitis and toxoplasmosis in the pregnant woman. Both are rare but can cause hydrocephalus.
Toxoplasmosis can result in congenital hydrocephalus if a woman becomes newly infected during her pregnancy. Toxoplasmosis is common in the UK, and is carried by cats in their faeces, and can also be found in undercooked or raw meats.
There is a group of disorders in which fluid-filled cysts develop in the CSF system.
In these cases, hydrocephalus is often due to pressure on the surrounding tissues by the enlarging cyst.
Dandy Walker Malformation is one of these conditions. It is a developmental disorder of the brain involving the cerebellum (part of the brain at the nape of the neck) and corpus callosum (band of brain tissue connecting the two halves of the brain) which results in enlargement of the fourth ventricle, causing the cyst.
Other developmental disorders of the brain can cause severe hydrocephalus, with a very poor outlook for the baby. Holoprosencephaly is a condition in which the embryonic brain fails to divide into the usual two hemispheres. Porencephaly is a rare condition in which a cyst or cavity within the brain fills with fluid. It can damage or destroy brain tissue, create pressure on the brain tissue, and cause hydrocephalus.
This occurs after birth and causes will include:
Anything that causes bleeding into the CSF can result in hydrocephalus. This can include subarachnoid haemorrhage (bleeding into the space between the meninges) and traumatic head injury. It is thought that the blood cells block the delicate cells that absorb the CSF. Blood clots can also block the CSF channels from ventricle to ventricle.
Babies born prematurely are at greater risk of developing hydrocephalus than a baby born at full term. The area just beneath the lining of the ventricles in the brain is particularly important – its blood vessels are very fragile and can burst if the baby suffers too large a swing in blood pressure, for example, from a blood clot or haemorrhage, and this can cause hydrocephalus. Lots of research has led to an improvement of the care of premature babies, which has reduced the number of babies having haemorrhages, and pioneered treatments for those babies that do have haemorrhages. Now only around 5% of premature babies need treatment for hydrocephalus.
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. (Brain haemorrhage and tumours may also occur congenitally).
This is an infection of the membranes covering the brain. The inflammation and debris from this infection block the drainage pathways resulting in hydrocephalus. Meningitis can occur at any age, but it is more common in early childhood, and in young adults. It can also result from bacteria in the birth canal, particularly Group B Streptococcus. There are several vaccines in the NHS vaccination schedule against different types of meningitis. These include-HIB, Pneumococccal, Men B and Men C for babies, and Men ACWY offered at around 14 years old.
Wherever possible, babies and young people with hydrocephalus should have all the vaccines offered. If your child has a fever, has had a bad reaction to a previous vaccine, or is on treatments such as steroids, chemotherapy or immunosuppressant drugs, talk with your GP, practice nurse or health visitor for guidance first.
Seen in older adults, NPH is characterised by dementia, decreased mobility and urinary incontinence.
Most babies born with spina bifida have hydrocephalus. In addition to the lesion in the spinal cord, structural abnormalities in parts of the brain can develop before birth. This prevents proper drainage of the CSF which increases the pressure and can compress the brain further.
