Chronic Hydrocephalus

Chronic hydrocephalus is persistent abnormal CSF accumulation producing progressive ventricular enlargement over weeks, months or years.

Important forms are:

Obstructive hydrocephalus

Persistent anatomical obstruction to CSF flow.

Communicating hydrocephalus

Failure of CSF absorption despite patent ventricular pathways.

Normal pressure hydrocephalus

A chronic communicating syndrome, usually in older adults, with ventriculomegaly and characteristic gait, cognitive and urinary dysfunction.

Hydrocephalus ex vacuo

Ventricular enlargement secondary to loss of brain tissue.

This is not true CSF pressure hydrocephalus and does not benefit from shunting simply because ventricles are large.

Chronic raised pressure hydrocephalus

Symptoms can include:

• Headache
• Cognitive slowing
• Gait dysfunction
• Visual disturbance
• Papilloedema
• Urinary dysfunction

Normal pressure hydrocephalus

The characteristic sequence is:

Gait impairment

Usually appears first.

Typical gait:

• Short stepped
• Broad based
• Slow
• Difficulty initiating walking
• Feet appear \"stuck\" to the floor

Cognitive impairment

Predominantly:

• Psychomotor slowing
• Reduced attention
• Executive dysfunction

rather than isolated cortical amnesia.

Urinary urgency or incontinence

Usually appears later.

The complete triad is not required for diagnosis.

MRI brain: preferred.

Assess:

• Ventricular enlargement
• Obstructive lesion
• Periventricular CSF signal
• Aqueduct
• Fourth ventricle
• Cerebral atrophy

In suspected NPH, an Evans index greater than approximately 0.30 supports ventriculomegaly but is not diagnostic alone.

Other supportive features include disproportionately enlarged ventricles relative to cortical sulci and a narrow high convexity subarachnoid space.

CSF tap test

For suspected NPH:

Remove approximately 30 to 50 mL CSF by lumbar puncture.

Measure objective gait function before and after the procedure.

Improvement in gait after CSF removal supports likely shunt responsiveness.

A negative tap test does not completely exclude benefit.

Extended lumbar drainage over several days can improve prediction in selected equivocal patients.

Ventriculoperitoneal shunt

VP shunting is the most common definitive CSF diversion operation.

Components are:

• Ventricular catheter
• Valve
• Distal peritoneal catheter

Programmable valves permit postoperative adjustment of opening pressure without another operation.

A practical approach is to start at a moderate pressure setting and gradually reduce it according to:

• Symptoms
• Ventricular response
• Development of overdrainage

NPH

The symptom most likely to improve after shunting is gait dysfunction.

Urinary symptoms can also improve.

Cognitive recovery is less predictable, particularly when there is established neurodegenerative disease.

A patient with ventriculomegaly alone and no compatible clinical syndrome should not undergo a shunt.

Obstructive hydrocephalus

Treat the underlying obstruction when possible.

Options include:

• Tumour removal
• Colloid cyst removal
• Aqueductal lesion treatment
• ETV

ETV is particularly attractive for anatomically suitable obstructive hydrocephalus and avoids lifelong shunt dependence in successful cases.

Shunt malfunction

Suspect with recurrence of:

• Headache
• Vomiting
• Drowsiness
• Gait deterioration
• Cognitive deterioration
• Visual symptoms
• Ventricular enlargement

Mechanical causes include:

• Proximal catheter obstruction
• Valve malfunction
• Distal catheter obstruction
• Disconnection
• Migration

Shunt infection

Features include:

• Fever
• Wound erythema
• Abdominal pain
• Meningism
• Neurological decline
• Positive CSF cultures

Established shunt infection usually requires:

• Remove infected shunt
• Temporary external ventricular drainage where necessary
• Culture directed IV antibiotics
• Reimplant a new shunt only after infection control

Antibiotics alone with infected hardware left permanently in place frequently fail.

Overdrainage

Excessive CSF drainage can produce:

• Orthostatic headache
• Slit ventricles
• Subdural hygroma
• Chronic subdural haematoma

Increase programmable valve opening pressure or add anti siphon control when appropriate.