Adult hydrocephalus and shunt complications
- In hydrocephalus, the cerebral ventricles dilate due to a disturbed circulation of cerebrospinal fluid (CSF). It is treated with a shunt that drains CSF out of the ventricles.
- No effective pharmacotherapy exists for hydrocephalus – as opposite to glaucoma where therapeutic options exists for a comparable problem in the aqueous humour circulation of the anterior chamber of the eye.
- Shunt blockage, infection or over- or underdrainage are possible. The shunt may predispose the patient to subdural haematoma, it may no longer be needed or it may, being an implant, cause subcutaneous discomfort.
- If the patient presents with signs and symptoms suggestive of increased intracranial pressure (Increased intracranial pressure), he/she must be transferred without delay to a hospital where an emergency head CT or MRI scan can be performed at all hours.
- Approximately 500 ml of CSF is formed within the brain each day, principally in the lateral ventricles. From the lateral ventricles CSF passes first to the 3rd ventricle then, through the aqueduct of Sylvius, to the 4th ventricle. From there it flows to the outer surfaces of the brain to be reabsorbed into the bloodstream via the arachnoid villi.
- The connection of the CSF circulation and hydrocephalus to the cerebral glymphatic system is for the time being unclear.
- Intracranial pressure – normally less than 10 cm H2O – is increased in hydrocephalus, either intermittently or consistently.
- Obstructive (non-communicating) hydrocephalus develops as a result of an obstruction in the normal circulation of CSF within the ventricles, and the ventricles proximal to the obstruction dilate.
- In communicating hydrocephalus all the ventricles dilate as the flow of CSF is either blocked in the subarachnoid space or its reabsorption via the arachnoid villi is impaired.
The aim and structure of a shunt
- A shunt is one of the most important human implants. It is not, however, technically ideal but is prone to complications.
- The aim of a shunt is to divert the CSF flow from the ventricles so as to relieve hydrocephalus and render the patient symptom-free.
- The patient’s life and functional capacity may be totally dependent on the shunt for the duration of his/her life.
- In normal pressure hydrocephalus (NPH), the aim of a shunt is to alleviate the symptoms (memory problems, gait disturbance, bladder control problems).
- A shunt consists of two silicone catheters with a valve mechanism in between them. The proximal catheter is inserted into the right lateral ventricle through a burr hole in the forehead or occipital region. The distal catheter is tunnelled subcutaneously to the peritoneal cavity or through an incision below the chin to the internal jugular vein and the right atrium of the heart.
- The valve usually sits behind the right ear. Valve opening pressure prevents excessive flow of CSF through the shunt. The opening pressure of a magnetic valve can be adjusted non-invasively through the skin. MRI of the head may alter the opening pressure (see below).
- Pressing of the valve does not have any diagnostic significance, at least not in unexperienced hands.
- The catheters and valve are easily identifiable in plain x-rays and CT scans of the skull, chest and abdominal cavity. The ventricular catheter and the valve cause an imaging artefact on an MRI scan of the head.
Shunt malfunction and other problems
- Many factors may cause the proximal catheter, the valve mechanism or the distal catheter to become blocked.
- The cause is often not identified.
- Presence of blood or a high number of cells or proteins in the CSF
- The catheter may become disconnected or the patient may outgrow the shunt (native x-ray along the whole course of the shunt).
- Adhesions or a cyst may develop around the tip of the peritoneal catheter (ultrasonography or CT scan).
- A patient who is fully dependent on the shunt is in immediate danger to life within a few hours if the shunt is blocked.
- If the clinical picture and the imaging findings indicate shunt blockage, the patient must be immediately transferred to a neurosurgical unit for shunt revision.
- Depending on the local circumstances and organisation of care, there may be a possibility for teleconsultation by sending the digital CT or MRI scans directly to the specialist on call at the neurosurgical unit and together with him/her negotiate about the need of emergency care.
- The first aid skills – including intubation skills – required of the person who will accompany the patient to the hospital should also be defined.
- In an emergency situation, puncture of the shunt chamber with e.g. a butterfly needle may be considered in order to tap out fluid and thus relieve the pressure symptoms.
- In some magnetic valves the opening pressure may be altered during MRI scanning (independent of the body part the imaging is directed at), and the opening pressure of such valves must be checked after MRI scanning.
- An infection of a shunt in an adult manifests itself as bacteraemia and persistent fever.
- An infected shunt almost always must be removed and replaced.
- If shunt nephritis develops as a result of an implanted ventriculoatrial shunt, the shunt must be replaced by a ventriculoperitoneal shunt.
- The penetration of the valve or catheter through the skin requires immediate management.
- In the slit ventricle syndrome the cerebral ventricles appear collapsed, and the patient complains of headaches.
- Adding an anti-syphon device to the shunt system may prevent overdrainage when the patient is in the upright position.
- Changing to a magnetic valve, which allows the adjustment of the opening pressure, often alleviates the situation.
- If underdrainage is suspected, the appropriate position of the shunt in its whole length is first confirmed through imaging.
- The function of the shunt may be assessed by an infusion test apparatus within a neurosurgical unit.
- A shunt predisposes the patient to chronic subdural effusion or haematoma.
- The treatment may require burr hole evacuation and/or adjustment of the opening pressure of the shunt valve.
- The shunt may be dispensed with, for example after an excision of a tumour or if the aetiology of the symptoms proves to be Alzheimer’s or some other neurodegenerative disease and not NPH.
- An unnecessary shunt is usually removed if the distal catheter is in the bloodstream (risk of shunt nephritis), if the shunt is problematic or if the patient is young.
- The shunt should be closed for a trial period before it is explanted. The proximal catheter is not necessarily removed because the pulling out may be associated with a risk of ventricular bleeding.
- The patient may feel that the valve or the catheters are too prominent under the skin or they may be uncomfortable. Neurosurgical consultation may be warranted.
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