Hydrocephalus

An abnormal accumulation of cerebrospinal fluid within the cerebral ventricular system, resulting from an imbalance between cerebrospinal fluid production and absorption, or from obstruction to its normal circulatory pathway.

It produces ventricular dilation. Depending on the underlying cause, timing, and rate of development, the clinical presentations range from acute, life threatening raised intracranial pressure through to the more insidious, characteristic triad of gait disturbance, cognitive impairment and urinary incontinence associated with normal pressure hydrocephalus in older adults.

Accurate classification by underlying mechanism (obstructive versus communicating) and by the specific clinical context is essential to guiding appropriate, targeted management.

Classification and pathophysiology

• Obstructive (non-communicating) hydrocephalus results from a structural obstruction to cerebrospinal fluid flow within the ventricular system itself, including at the level of the foramen of Monro, cerebral aqueduct, or fourth ventricular outflow foramina.
• Common causes are a mass lesion, congenital aqueductal stenosis or, in the context of infection or haemorrhage, inflammatory adhesion or debris obstructing the normal narrow flow pathways.
• Communicating hydrocephalus results from impaired cerebrospinal fluid absorption at the level of the arachnoid granulations (the normal site of cerebrospinal fluid reabsorption into the venous system), without any obstruction to flow within the ventricular system itself.
• It commonly results from prior subarachnoid haemorrhage or meningitis.
• In normal pressure hydrocephalus the mechanism remains incompletely understood, despite the clinical significance and relative frequency of this presentation.
• Normal pressure hydrocephalus is a specific, important clinical entity characterised by ventricular dilation with, characteristically, normal or only intermittently elevated cerebrospinal fluid pressure on standard, single point in time measurement.
• It presents with a characteristic clinical triad.
• It is one of the relatively few potentially reversible causes of an otherwise dementia-like clinical presentation in older adults.

• Acute hydrocephalus, developing rapidly over hours to days, presents with the classical features of acutely raised intracranial pressure.
• These include headache (often severe, and characteristically worse with recumbency or with manoeuvres that increase intracranial pressure such as coughing or straining), nausea and vomiting, and papilloedema.
• In more severe or rapidly progressive presentations there is reduced consciousness. In infants with open cranial sutures there is characteristic progressive head circumference enlargement.
• It is a neurosurgical emergency requiring urgent recognition and intervention.
• Chronic hydrocephalus, developing more gradually, may present with a more insidious pattern of headache, cognitive change, and gait disturbance, with the specific clinical presentation varying according to the underlying cause and the rate and degree of ventricular dilation.
• Normal pressure hydrocephalus presents with a characteristic clinical triad:
  • gait disturbance: typically a broad based, shuffling, "magnetic" gait, sometimes described as appearing as though the feet are stuck to the floor; frequently the earliest and most prominent component of the triad
  • cognitive impairment: typically a subcortical pattern with prominent psychomotor slowing and executive dysfunction, generally with relative preservation of episodic memory compared with Alzheimer disease, at least in the earlier stages
  • urinary incontinence: typically developing later in the clinical course, following the gait and cognitive symptoms
• The combination and relative severity of the three components vary between affected individuals.
• The full triad is not necessarily present in every case, particularly earlier in the clinical course.
• Congenital hydrocephalus in infants presents with progressive, disproportionate head circumference enlargement, together with a tense, bulging anterior fontanelle and prominent scalp veins.
• In more advanced or rapidly progressive cases there is the characteristic "sunsetting" sign: downward deviation of the eyes with visible sclera above the iris, reflecting pressure effects on the midbrain tectum.
• This is a distinct clinical presentation reflecting the unique physiological context of the open cranial sutures characteristic of this age group.

• Computed tomography or magnetic resonance imaging of the brain confirms ventricular dilation and, importantly, helps identify the underlying cause and mechanism (obstructive versus communicating).
• Magnetic resonance imaging is generally preferred where feasible, given superior anatomical detail, particularly valuable for identifying the site of any obstruction in obstructive hydrocephalus.
• Normal pressure hydrocephalus diagnosis is supported by the characteristic clinical triad together with the imaging finding of ventricular dilation disproportionate to any accompanying cortical atrophy.
• A large volume lumbar puncture, removing a substantial volume (typically 30 to 50 mL) of cerebrospinal fluid, is a valuable diagnostic test. Formal, structured assessment of gait and cognitive function is done before and after the procedure.
• Clear, objective improvement following the large volume tap supports the diagnosis and predicts a favourable response to definitive surgical shunt treatment.
• This is an important, practical diagnostic and prognostic tool, given the potentially reversible nature of this condition and its direct relevance to appropriate patient selection for surgical intervention.
• Extended lumbar drainage may be used in some centres as a further, more extended diagnostic and prognostic test where the response to a single large volume tap is equivocal.
• It uses a temporary, indwelling lumbar drain over several days, with continued formal assessment of gait and cognitive function.
• It offers a more prolonged period of assessment before committing to permanent surgical shunt placement.
• Careful, full assessment to exclude alternative causes of the presenting clinical picture is essential across the hydrocephalus spectrum.
• This is particularly relevant for normal pressure hydrocephalus. Exclusion of alternative causes of gait disturbance and cognitive impairment, addressed under major neurocognitive disorder generally, is an essential component of diagnostic evaluation.
• There is significant clinical overlap with several other, generally non-reversible, causes of a dementia-like presentation in this older patient population.

• Acute, symptomatic hydrocephalus represents a neurosurgical emergency requiring urgent cerebrospinal fluid diversion, typically via external ventricular drain placement in the acute setting, providing both immediate therapeutic relief of the elevated intracranial pressure and an opportunity for ongoing monitoring and, where relevant, cerebrospinal fluid sampling.
• Definitive, longer term management of persistent or chronic hydrocephalus generally requires surgical cerebrospinal fluid diversion.
• Ventriculoperitoneal shunt placement is most common: a surgically implanted catheter system diverting cerebrospinal fluid from the ventricular system to the peritoneal cavity for reabsorption.
• Endoscopic third ventriculostomy creates a surgical opening within the floor of the third ventricle to bypass a specific obstruction and restore more normal cerebrospinal fluid flow.
• It is an alternative, shunt-avoiding approach, particularly relevant and effective for selected cases of obstructive hydrocephalus with a suitable underlying anatomical cause and pattern.
• Any underlying, specific causative structural lesion (a mass lesion causing obstructive hydrocephalus) requires its own, specific targeted treatment according to the particular underlying pathology, addressed under the relevant individual conditions, alongside the cerebrospinal fluid diversion procedure itself.
• Normal pressure hydrocephalus, where supported by a favourable response to large volume lumbar puncture or extended lumbar drainage testing, is managed with ventriculoperitoneal shunt placement.
• The gait disturbance component of the clinical triad generally shows the most consistent, substantial improvement following successful shunt treatment.
• The cognitive and urinary incontinence components show a more variable, generally somewhat less complete degree of improvement.
• This is an important point for patient and family counselling and realistic expectation setting regarding the anticipated outcome of surgical treatment.
• Ongoing monitoring for and prompt recognition of shunt related complications is an essential component of long term management, given the recognised, lifelong risk in any patient with an indwelling cerebrospinal fluid shunt system.
• Shunt malfunction or obstruction presents with recurrence of the original presenting symptoms. It requires urgent reassessment and, where confirmed, surgical shunt revision.
• Shunt infection presents with fever and signs of meningitis or, where relevant, peritonitis, given the distal shunt catheter location.
• It requires prompt antimicrobial treatment and, generally, surgical shunt removal or externalisation, together with subsequent staged reinsertion once infection is confirmed cleared.
• Congenital hydrocephalus in infants is managed with surgical cerebrospinal fluid diversion following similar general principles.
• Full, ongoing paediatric neurosurgical and developmental follow up is needed, given the potential for associated neurodevelopmental impact.
• The underlying cause, where identifiable, informs the overall prognosis and the individualised management approach for the affected infant. Causes include specific congenital structural abnormalities or the sequelae of intraventricular haemorrhage of prematurity.