Hydrocephalus

Shunt techniques

A reservoir permits CSF aspiration for analysis. A valve is incorporated in system, with either

- fixed opening pressure e.g. Hcyer-Schulte, Hakim

- variable opening pressure (flow regulated) e.g. Orbis sigma, Delta

- programmable e.g. Medos, Sophy.

Valve opening pressures range from 5-150 mm HzO

„.--A ventricular catheter is inserted through the occipital (or frontal) horn. The tip lies at the level of the foramen of Munro.

[Lumboperitoneal shunt - catheter inserted into the lumbar theca either ':, directly at open operation or percutaneously through a Tuohy -

needle. The distal end is sited in the peritoneal cavity.]

„.--A ventricular catheter is inserted through the occipital (or frontal) horn. The tip lies at the level of the foramen of Munro.

Ventriculoatrial shunt - distal catheter inserted through the internal jugular vein to the right atrium (T6/7 level on chest X-ray).

— Silastic tubing tunnelled subcutaneously.

Ventriculoperitoneal shunt - distal --' catheter inserted into the peritoneal cavity. In children, redundant coils permit growth without revision.

Complications of shunting

Infection-, results in meningitis, peritonitis or inflammation extending along the subcutaneous channel. In patients with a V-A shunt, bacteraemia may lead to shunt 'nephritis'. Staphylococcus epidermidis or aureus are usually involved, with infants at particular risk. Prophylactic antibiotics may minimise the risk of infection, but, when established, eradication usually requires shunt removal.

Subdural haematoma: ventricular collapse pulls the cortical surface from the dura and leaves a subdural CSF collection or tears bridging veins causing subdural haemorrhage. This risk may be reduced with a variable pressure or programmable valve.

Shunt obstruction-, blockage of the shunt system with choroid plexus, debris, omentum or blood clot results in intermittent or persistent recurrence of symptoms and indicates the need for shunt revision. Demonstration of an increase in ventricular size compared to a previous baseline CT scan confirms shunt malfunction. Over a third require revision within 1 year and 80% within 10 years.

Low pressure stare: following shunting, some patients develop headache and vomiting on sitting or standing. This low pressure state usually resolves with a high fluid intake and gradual mobilisation. If not, insertion of an antisyphon device or conversion to a high pressure valve is required.

Third Ventriculostomy: In patients with obstructive hydrocephalus, creating a hole in the floor of the third ventricle via a flexible or rigid endoscope, provides an alternative method of treatment which, if successful, avoids the problem of shunt obstruction, infection and over drainage.

Prognosis: Provided treatment precedes irreversible brain damage, results are good with most children attaining normal IQs. Repeated complications, however, particularly prevalent in infancy and in young children carry a significant morbidity.

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