Shunts remain the mainstay of treatment for hydrocephalus and, in the majority of cases, this remains an effective treatment.
However, they can never perfectly mimic normal physiology and, like any mechanical device, they are prone to malfunctions of various sorts.
Shunt blockage, along with shunt infection, remains the commonest cause of shunt malfunction. In the vast majority of cases of shunt blockage prompt investigation and revision of the shunt is associated with full recovery and discharge from hospital within a few days. In rare situations shunt blockage can be fatal, particularly when the diagnosis is delayed.
There hasn't been a significant improvement in the level of blockages in recent years. The rate of shunt blockages is highest in the first year after insertion, when it can be in the order of 20-30% - decreasing to approximately 5% per year thereafter. Over half of patients who have a shunt fitted will need at least one shunt revision in the following 10 year period.
Obstruction can occur in any part of the shunt. If the shunt is not working properly, either all or part of it will need to be replaced. It is the ventricular catheter (the part of the shunt that passes into the ventricles of the brain) where the shunt most commonly blocks. The holes in the shunt tubing may become obstructed by the choroid plexus (this is the membrane which manufactures the CSF) or by a build up of cellular debris.
The clinical presentation is usually dominated by signs of raised pressure as the brain fluid (CSF) builds up. This increase in pressure results in symptoms of, most typically, headache, vomiting and drowsiness. Sometimes the symptoms come on quickly over hour or days, but occasionally they may develop over many weeks with intermittent headache, and tiredness, change in behaviour or deterioration in schoolwork. In babies an enlarging head circumference, bulging fontanelle (the soft part at the top of the head), CSF tracking along the course of the shunt and, rarely, seizures, are additional indicators of underlying shunt malfunction.
Less common symptoms include seizures, abdominal swelling (due to malabsorption of CSF by the peritoneum or encysting of CSF in the peritoneal cavity), cranial nerve palsies (particularly in the spina bifida child).
If a shunted child becomes unwell, it's important that the possibility of a shunt blockage be considered (and hopefully excluded) as soon as possible.
Two prospective studies of 104 admissions to the paediatric neurosurgical unit at Great Ormond Street Hospital NHS Trust showed that drowsiness was by far the best, but not definite, clinical predictor of shunt blockage. Headache, vomiting and irritability were less predictive as to whether the child's shunt was actually blocked, and nor was the duration of the symptoms. The presence of a raised temperature suggests an alternative diagnosis for the symptoms or may indicate that the shunt is malfunctioning because it is infected.
It is important that children who have had treatment for hydrocephalus (this includes those who have had endoscopic third ventriculostomy) and their families are aware of the symptoms and signs of shunt blockage and who to contact if they are concerned. Most paediatric neurosurgical units provide 24hr telephone advice and many offer an open access policy for children who have shunts.
Diagnosing shunt blockage is not always straightforward. Commonly there will be an alternative explanation for the symptoms for example ear infection, common colds etc. In fact, parents can be as successful at diagnosing shunt blockage as GPs and paediatricians.
Whilst additional investigations such as CT scan, plain X-rays and a shunt tap may be decisive, a definitive diagnosis is sometimes only possible through surgery.
Families should always be advised about shunt blockages, why and how they happen, at the time a shunt is first fitted. All children who have a shunt in situ should be registered with a designated neurosurgical unit to which they can be referred when the shunt goes wrong. If a child moves to another part of the country with their parents they must be reassigned to a new neurosurgical facility as soon as possible.
Families should have open access to their neurosurgical unit for emergency advice. Deteriorating conscious level visual failure/obscurations, neck pain/stiffness or slow pulse rate all imply dangerously elevated intracranial pressure and constitute a neurosurgical emergency. Urgent medical advice must be sought in this situation; this may mean that the child will be seen at their local hospital initially where doctors can stabilise the child's condition and liaise with the neurosurgical team regarding emergency transfer.
It is important to repeat that most children who develop a shunt blockage will make a full recovery once the problem is treated. Children with shunts are as prone to all the usual childhood ailments as children without and new symptoms or signs will commonly have an alternative explanation. It is always better to seek advice sooner rather than later - when in doubt shout!
