Hydrocephalus is commonly known as ‘water on the brain’. There are four cavities called ventricles inside the brain. A watery fluid known as cerebrospinal fluid (CSF) flows through narrow passageways in the brain from one ventricle to the next, out over the outside of the brain and down the spinal cord. CSF is continuously absorbed into the blood stream and the amount of pressure is kept within a narrow range. Hydrocephalus is where the flow of fluid is obstructed and then accumulates in the ventricles, causing them to enlarge and compress surrounding brain tissue and interfere with the blood supply to the brain. In babies – but not older children or adults – the head will enlarge. A form of hydrocephalus called “Normal Pressure Hydrocephalus” (NPH) can affect elderly people causing mental deterioration, walking difficulties and urinary incompetence.
Medical text written July 2015 by Professor R Bayston, Chair Health Council, Shine Charity, and Professor of Surgical Infection, University of Nottingham, Nottingham, UK.
The main symptom is headache, often with nausea, vomiting, dizziness, or vision difficulties. Sometimes balance can be affected and there may be difficulty in walking and hand coordination. In babies, the head size usually increases and this should be measured. Later, difficulty in raising the eyes to look upwards is seen. In NPH, slowly progressive mental deterioration, shuffling gait and tendency to fall backwards, along with urinary accidents can be seen in elderly people.
The most common causes of hydrocephalus in children are infections such as meningitis, or brain haemorrhage after premature birth, head injury (see entry Brain Injuries), or a brain tumour. Hydrocephalus is a common accompaniment of spina bifida. An uncommon cause in the UK is infection of the baby before birth, such as by toxoplasmosis. The cause of NPH is unclear.
Diagnosis of hydrocephalus follows clinical features such as excessively increasing head circumference in babies, headaches, vomiting. A CT scan or MRI will then determine whether the ventricles in the brain are too large, or if there is another cause.
Treatment is usually by insertion of a ‘shunt’ (a small tube -like device) to redirect the excess CSF to the abdomen or, less commonly, the heart. In some cases, a third ventriculostomy can be performed; this involves a tube called an endoscope being inserted into the brain and a hole being made in the floor of the third ventricle to allow CSF flow to resume. This operation avoids the use of a shunt but it is suitable only for certain types of hydrocephalus, and it is not as successful when carried out in babies. Symptoms caused by raised pressure usually improve after treatment, but other signs of brain damage may remain including subtle learning difficulties (see entry Learning Disability) and poor coordination. In NPH, considerable improvement is sometimes seen after shunting.
Shunts sometimes need to be surgically revised due to blockage or infection. Blockage can lead to return of the hydrocephalus symptoms. Shunts usually have fixed pressure settings and sometimes need an operation to change the shunt for a different setting. This can be avoided by insertion of an adjustable shunt that can be changed from the outside using a special magnet.
Shunt infection usually leads to shunt blockage, which has the symptoms mentioned above, but may also be accompanied by fever, abdominal pain and redness or swelling over the shunt catheter. Chronic infection may cause gradual deterioration in overall performance. In shunts draining into the heart, the symptoms are different and more complex, but a blood test is available for diagnosis. The risk of shunt infection has been considerably reduced by the use of antimicrobial shunts that resist infection.
Medical advice should be sought immediately in cases of mental or physical deterioration in those with shunts, or if a shunt blockage or infection is suspected.
Inherited hydrocephalus is very rare, and is usually X-linked, meaning that only boys are affected. It is usually accompanied by abduction of the thumbs. Diagnosis is determined by genetic tests.
Often, but not always, seen prenatally on ultrasound. Fetal scanning by magnetic resonance imaging (MRI) is recommended where hydrocephalus is suspected.
Information and support in the UK for hydrocephalus is provided by SHINE (Spina Bifida • Hydrocephalus • Information • Networking • Equality; see entry Spina Bifida).