Medicine – Normal Pressure Hydrocephalus

Normal pressure hydrocephalus (NPH) is a form of communicating hydrocephalus in which the cerebral ventricles enlarge because cerebrospinal fluid is not absorbed normally. Despite the name, CSF pressure measured at a single lumbar puncture may be normal because the pressure can fluctuate over time.

The classic clinical triad is:

Gait disturbance + cognitive impairment + urinary dysfunction.

A common memory aid is:

“Wet, wobbly and wacky.”

1. Basic Mechanism

Normal pressure hydrocephalus usually results from impaired CSF absorption, particularly at the arachnoid granulations.

This causes gradual accumulation of CSF within the ventricular system.

Therefore:

Reduced CSF absorption → ventricular enlargement → stretching/compression of periventricular white matter → gait, cognitive and bladder dysfunction.

2. CSF Pressure

The term normal pressure hydrocephalus can be misleading.

CSF pressure is not necessarily continuously normal.

Instead, patients may experience:

Intermittent rises in intracranial pressure.

A lumbar puncture performed at one moment may therefore show a pressure within the normal range.

3. Communicating Hydrocephalus

NPH is usually a form of:

Communicating hydrocephalus.

This means that CSF can still flow through the ventricular system, but its absorption into the venous circulation is impaired.

There is no fixed obstruction within the ventricles themselves.

4. Role of Meningeal Scarring

Previous inflammation or bleeding around the meninges can interfere with CSF absorption.

This may occur after:

Meningitis.

Subarachnoid haemorrhage.

Head injury.

These conditions can produce scarring of the arachnoid pathways and reduce CSF resorption.

5. Idiopathic NPH

Many patients have no clear preceding cause.

This is called:

Idiopathic normal pressure hydrocephalus.

It is particularly seen in older adults.

6. Secondary NPH

When there is an identifiable cause, it is called:

Secondary NPH.

Important causes include:

Subarachnoid haemorrhage.

Meningitis.

Head trauma.

Previous neurosurgery in some cases.

7. Classic Clinical Triad

The classic triad consists of:

Gait disturbance.

Cognitive impairment.

Urinary dysfunction.

Gait disturbance is usually the earliest and most prominent feature.

8. Gait Disturbance

The gait abnormality is classically described as:

Magnetic gait.

The patient’s feet appear to be:

“Glued to the floor.”

There may be difficulty initiating walking, with short shuffling steps and a broad-based unsteady gait.

9. Magnetic Gait

Patients may have particular difficulty:

Starting to walk.

Turning.

Lifting the feet from the floor.

Maintaining balance.

The legs may appear weak or slow despite relatively preserved strength on formal testing.

10. Gait versus Parkinson Disease

The gait of NPH can resemble parkinsonism, but there are useful differences.

NPH tends to produce:

Broad-based gait.

Short steps.

Difficulty initiating gait.

Feet appearing stuck to the floor.

Parkinson disease more typically includes:

Bradykinesia.

Rigidity.

Reduced arm swing.

Rest tremor in some patients.

However, overlap can occur.

11. Cognitive Impairment

The older term dementia is often used in the classic triad, but early NPH more typically produces a subcortical/frontal cognitive syndrome.

Features can include:

Mental slowing.

Poor attention.

Reduced concentration.

Executive dysfunction.

Apathy.

Memory difficulty.

12. Frontal Lobe Dysfunction

The cognitive and bladder features are partly related to dysfunction of frontal-subcortical pathways running near the enlarged ventricles.

This explains why NPH can produce:

Executive dysfunction.

Reduced initiative.

Urinary urgency or incontinence.

13. Urinary Dysfunction

Bladder symptoms often begin with:

Urinary urgency.

and

Increased frequency.

Later, patients may develop:

Urinary incontinence.

Therefore, urinary incontinence is usually a later feature rather than necessarily the first bladder symptom.

14. Sequence of Symptoms

A useful clinical pattern is:

Gait disturbance first.

Then:

Cognitive decline.

Then:

Urinary dysfunction.

This sequence is not absolute, but gait abnormality is often the earliest and most treatment-responsive feature.

15. Causes of NPH

Important causes include:

Meningitis.

Head injury.

Subarachnoid haemorrhage.

These may impair CSF absorption through arachnoid scarring.

16. Meningitis

Previous meningitis can cause inflammation and scarring of the meninges.

This can impair CSF absorption and result in communicating hydrocephalus.

Therefore:

Meningitis → meningeal scarring → impaired CSF absorption → hydrocephalus.

17. Subarachnoid Haemorrhage

Subarachnoid haemorrhage is an important acquired cause.

Blood within the subarachnoid space may interfere with arachnoid granulation function.

This can result in:

Reduced CSF resorption.

and

Communicating hydrocephalus.

18. Head Injury

Significant head injury can also disturb CSF absorption.

Post-traumatic inflammation, haemorrhage, or scarring may eventually contribute to hydrocephalus.

19. Brain Imaging

Brain imaging usually demonstrates:

Ventriculomegaly.

This means enlargement of the ventricles.

The ventricular enlargement is typically greater than would be expected from ordinary age-related cerebral volume loss.

20. Ventricular Dilatation

The ventricles, particularly the lateral ventricles, become enlarged.

Therefore:

Dilated ventricles are a central radiological feature of NPH.

This reflects hydrocephalus rather than simple loss of brain tissue alone.

21. Cortical Atrophy – Important Clarification

The original note lists:

Cortical atrophy.

However, cortical atrophy is not the defining radiological feature of NPH.

In fact, an important diagnostic issue is distinguishing:

Ventricular enlargement due to hydrocephalus

from

Ventricular enlargement due to cerebral atrophy.

The latter is called:

Hydrocephalus ex vacuo.

22. Hydrocephalus Ex Vacuo

In cerebral atrophy, brain tissue volume decreases and the ventricles enlarge passively.

This is not true NPH.

Therefore:

NPH → ventricles enlarged disproportionately to cortical atrophy.

Hydrocephalus ex vacuo → ventricles enlarged because the brain itself has atrophied.

This distinction is important.

23. CT and MRI Findings

CT or MRI may demonstrate:

Enlarged lateral ventricles.

Enlargement of the third ventricle.

Disproportionate ventriculomegaly.

Periventricular signal change from transependymal CSF flow in some patients.

MRI can also help assess the pattern of sulci and other features supporting NPH.

24. DESH Pattern

A useful modern imaging pattern is:

Disproportionately enlarged subarachnoid-space hydrocephalus, or DESH.

This can include:

Ventriculomegaly.

Relatively tight high-convexity sulci.

Relatively enlarged Sylvian fissures.

This pattern can support the diagnosis of NPH.

25. Evans Index

Ventricular enlargement may be quantified using the:

Evans index.

This compares the width of the frontal horns of the lateral ventricles with the internal diameter of the skull.

An elevated value supports ventriculomegaly, although imaging diagnosis should not rely on this measurement alone.

26. Diagnosis

Diagnosis combines:

Typical clinical features.

Compatible brain imaging.

Assessment of response to CSF removal.

The clinical picture and imaging should be interpreted together.

27. Lumbar Puncture

A diagnostic lumbar puncture may be performed.

The opening pressure is often:

Normal or only mildly elevated.

More importantly, removal of a relatively large volume of CSF may temporarily improve symptoms.

28. Large-Volume Tap Test

The CSF tap test involves removing CSF by lumbar puncture and then reassessing the patient’s function.

Particular attention is paid to:

Walking speed.

Step length.

Balance.

Gait initiation.

Improvement after CSF removal supports the possibility that shunting may be beneficial.

29. External Lumbar Drainage

In selected cases, temporary:

External lumbar drainage

may be used when the diagnosis remains uncertain.

A more sustained improvement in gait or cognition after drainage can support shunt responsiveness.

30. Treatment

The principal treatment for symptomatic NPH in appropriately selected patients is:

CSF shunt surgery.

The commonest procedure is:

Ventriculoperitoneal shunting.

31. Ventriculoperitoneal Shunt

A ventriculoperitoneal shunt drains CSF from the:

Cerebral ventricles

to the:

Peritoneal cavity.

This lowers ventricular CSF volume and may improve neurological function.

32. Response to Treatment

The symptom most likely to improve after successful shunting is:

Gait disturbance.

Urinary symptoms may also improve.

Cognitive impairment can improve, but response is more variable, particularly if longstanding or if another neurodegenerative disorder is present.

33. Shunt Complications

Potential complications include:

Infection.

Shunt blockage.

Over-drainage.

Subdural haematoma or hygroma.

Mechanical failure.

Therefore, careful patient selection is important.

34. Important Differential Diagnoses

Conditions that can resemble NPH include:

Parkinson disease.

Vascular parkinsonism.

Alzheimer disease.

Lewy body dementia.

Cervical myelopathy.

Peripheral neuropathy.

Medication effects.

Hydrocephalus ex vacuo from cerebral atrophy.

35. NPH versus Alzheimer Disease

NPH often presents with:

Gait disturbance early.

Frontal-subcortical cognitive slowing.

Urinary symptoms.

Alzheimer disease more characteristically begins with:

Progressive episodic memory impairment.

A prominent early magnetic gait should therefore raise suspicion for NPH rather than uncomplicated Alzheimer disease.

36. Normal Pressure Hydrocephalus – Note Form

Type: communicating hydrocephalus.

Mechanism: impaired CSF absorption.

Pressure: may fluctuate; a single lumbar puncture may show normal pressure.

Classic triad: gait disturbance + cognitive impairment + urinary dysfunction.

Gait: magnetic gait, “feet glued to the floor.”

Cognition: frontal/subcortical slowing and executive dysfunction.

Bladder: urgency/frequency followed by possible incontinence.

Causes: idiopathic, meningitis, subarachnoid haemorrhage, head injury.

Imaging: ventriculomegaly disproportionate to cerebral atrophy.

Diagnostic support: improvement following CSF removal.

Treatment: ventriculoperitoneal shunt in suitable patients.

37. Important Correction to the Original Radiology Note

The original sequence:

Cortical atrophy + dilated ventricles + hydrocephalus

can be misleading.

A better way to remember the radiology is:

NPH → enlarged ventricles out of proportion to cortical atrophy.

If ventricular enlargement is simply due to severe cortical atrophy, consider:

Hydrocephalus ex vacuo rather than NPH.

Key Clinical Pattern

Think:

NORMAL PRESSURE HYDROCEPHALUS = GAIT + COGNITION + BLADDER.

The classic sequence is:

MAGNETIC GAIT → COGNITIVE SLOWING → URINARY URGENCY/INCONTINENCE.

The underlying mechanism is:

Impaired CSF absorption → communicating hydrocephalus → ventriculomegaly.

On imaging:

Dilated ventricles disproportionate to cortical atrophy.

And treatment is:

Ventriculoperitoneal shunting in appropriately selected patients.