By Dr Roger Bayston MMedSci MRCPath
ASBAH's Honorary Consultant in Hydrocephalus
In the first article in this series, I explained that hydrocephalus involves accumulation of cerebrospinal fluid (CSF) in the ventricles of the brain, with an increase in the pressure inside the head.
There are two sources of this pressure. One is that of the CSF itself, but a much higher pressure is produced by the heart in order to pump blood to the brain. If the CSF pressure rises, it eventually interferes with the blood supply to the brain, depriving it of oxygen and glucose which it needs in constant amounts to continue to function. Initially this causes tiredness, irritability and drowsiness, but if it progresses then loss of consciousness will result as the brain begins to shut down.
The immediate effects of this interference with the blood supply disappear if the CSF pressure is returned to normal, such as by ventricular tap or insertion of a shunt. However, in most cases the process has been continuing for some time before diagnosis of hydrocephalus is made. During this time the interference with the blood supply leads first to a 'dying back' of the very fine blood vessels in the brain. Even this process is largely reversible if prompt action is taken, but at this time there is often insufficient clinical evidence to suspect hydrocephalus. The next stages involve progressive damage to the actual nerve cells in the brain and to their eventual destruction, and this cannot be reversed.
Because of the areas of the brain most affected, functions associated with thought and learning as well as with co-ordinated skilled movement begin to deteriorate. The precise effects differ between individuals and are further complicated by other abnormalities as well as by the pre-existing degrees of ability and personality of each person affected. It is not surprising therefore that while, for instance, learning disorders are common amongst those with hydrocephalus, their exact effects vary considerably.
Much is said and written about intelligence, and particularly about IQ (intelligence quotient) in people with hydrocephalus. In fact this is far more complicated, and a good deal less informative, than many believe. The IQ is made up of several components which can be thought of as verbal and non-verbal, or performance-related tests. People with hydrocephalus generally score better on verbal IQ than on performance IQ and this is thought to reflect the distribution of nerve damage in the brain as described above. Certainly during periods of rising CSF pressure, such as in untreated cases or when a shunt is blocked, the effect on performance IQ is more marked. Generally speaking, people who have had hydrocephalus since birth or childhood have, as a group, a lower average IQ than a comparable group without hydrocephalus, but it is important to realise that there is a wide range in each group, and some people with hydrocephalus have very high scores.
The practical implications of these features of hydrocephalus are that there may be subtle problems of co-ordination of hand movements with what the person sees, as well as a degree of clumsiness, which make it difficult to perform certain tasks or do certain jobs. With regard to learning in the home or to education in school, there may be real problems with concentration and reasoning which require a sympathetic but skilled approach. For instance, it will often be necessary to teach simple every day tasks like getting out of bed, washing one's face, dressing and going downstairs as separate short items rather than all at once, and to keep them consistent and repetitive. This does not indicate 'stupidity' but is caused by damage to the nerves in the brain which normally allow us to learn very quickly how to do a complex series of things. Much can be done to help, and professional advice should be sought where needed.
Psychological development in children and adolescents with hydrocephalus may proceed normally, but sometimes the changes associated with puberty (breast development, body hair growth etc) appear much earlier than expected, and the intrusion of psychological aspects of sexual development into a mind which is emotionally still very immature can cause distressing problems. Again, specialist advice should be sought if necessary.
Other effects of hydrocephalus may also be seen, and some of these are difficult to explain. For instance, some people are very seriously distressed by every day noises such as vacuum cleaners or washing machines.
One effect of raised CSF pressure may be seen in the eyes, and this is why your doctor sometimes looks for 'papilloedema'. This is caused by pressure on the blood supply to the back of the eye. It is important to realise that it may not always be present, even when the pressure is high. If CSF pressure remains high for too long, damage to the optic nerves can become permanent resulting in blindness, though fortunately nowadays this is uncommon. Another appearance, particularly in babies, is the so-called 'sunset' eye sign, where the eyes are fixed in a downward position. This is due to CSF pressure affecting important nerves running from the brain which control eye movement.
If untreated the rise in CSF pressure can cause other serious problems in the brain, unrelated to blood supply. Many of our vital functions such as heart beat, breathing etc are controlled from the brain stem, a structure joining the spinal cord to the brain. Very high CSF pressure can compress this sufficiently to cause the heart and breathing to stop. Once again this is uncommon as signs of raised pressure are usually recognised before this. A similar problem might sometimes arise, particularly in those with spina bifida, due to compression of the cerebellum, a part of the brain lying at the back of the head. This can also give rise to breathing, speaking and swallowing difficulties.
Reading a catalogue of effects of hydrocephalus such as I have produced here can be very alarming. However it should be realised that some people with hydrocephalus may have very few of these problems, and hopefully none of the more serious ones. Also, many of those which I have described are found either in untreated hydrocephalus or when the treatment fails, and when successful treatment has been promptly introduced they often improve or sometimes disappear. On the other hand, the more subtle learning and reasoning problems are usually present in some degree and are very important where a child's development and education are concerned.
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