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KEY FACTS

Terminology
- Ventriculomegaly with normal CSF pressure, altered CSF dynamics
- Idiopathic normal-pressure hydrocephalus (iNPH)
Imaging
- Enlarged lateral & 3rd ventricles, 4th ventricle relatively normal
- Evans index(ratio of widest diameter of frontal horns to widest diameter of brain on same axial slice) ≥ 0.3
- Callosal angle (angle between lateral ventricles on coronal image at level of posterior commissure) < 90°
- Disproportionately enlarged subarachnoid space hydrocephalus (DESH) (particularly sylvian fissures & basal cisterns)
- Cingulate sulcus sign: Narrowing of posterior cingulate sulcus compared with anterior
- Tight high convexity with effacement of parafalcine sulci
- Aqueductal flow void
- Aqueduct stroke volume (ASV) > 42 μL
Top Differential Diagnoses
- Normal aging brain
- Alzheimer disease
- Multiinfarct dementia (MID)
- Subcortical arteriosclerotic encephalopathy
Pathology
- Pathogenesis of iNPHpoorly understood & controversial
- Secondary NPH (sNPH): Subarachnoid hemorrhage, meningitis, neurosurgery, or head trauma)
Clinical Issues
- Heterogeneous syndrome (classic clinical triad = dementia, gait apraxia, urinary incontinence)
Diagnostic Checklist
- Is ventricular dilation solely due to atrophy?
- Diagnostic challenge = identify shunt-responsive NPH

TERMINOLOGY

Abbreviations
- Normal-pressure hydrocephalus (NPH)
Synonyms
- Idiopathic adult hydrocephalus syndrome
Definitions
- Ventriculomegaly with normal CSF pressure, altered CSF dynamics

IMAGING

General Features

Best diagnostic clue

- Enlarged lateral & 3rd ventricles, 4th ventricle relatively normal
- Ventricular enlargement out of proportion to generalized sulcal enlargement
- Disproportionately enlarged subarachnoid space hydrocephalus (**DESH**) (particularly sylvian fissures & basal cisterns)
- High tight convexity with effacement of sulci at vertex

Location

- Ventriculomegaly involves all 3 horns of lateral ventricles, plus 3rd ventricle
        - 4th ventricle relatively spared

Size

- **Evans index**(ratio of widest diameter of frontal horns to widest diameter of brain on same axial slice) ≥ 0.3
- **Callosal angle** (angle between lateral ventricles on coronal image at level of posterior commissure) < 90°
- Widening of temporal horn > 6 mm

Morphology
```
- Diffuse expansion of ventricles
```

CT Findings

NECT

- Ventriculomegaly with rounded frontal horns, out of proportion to sulcal atrophy (ventriculosulcal disproportion)
- Frontal/occipital periventricular hypodensities may be present
- Corpus callosal thinning (nonspecific)
- Prominent basal cisterns & sylvian fissures

MR Findings
- Lateral ventricles enlarged with rounded frontal horns
- Focal bulging of roof of lateral ventricles
- Moderately dilated 3rd ventricle, relatively normal 4th ventricle
- Dilatation of optic & infundibular recesses of anterior 3rd ventricle
- Cingulate sulcus sign: Narrowing of posterior cingulate sulcus compared with anterior
- DESH
- High tight convexity with effacement of parafalcine sulci
- Corpus callosum bowed upward (may be impinged by falx)
- Aqueductal flow void sign - Reflects increased CSF velocity through cerebral aqueduct - May be reduced if flow compensation, fast spin-echo techniques used
- Periventricular "halo" high signal, primarily anterior to frontal horns or posterior to occipital horns of lateral ventricles - 50-60% have periventricular & deep white matter (WM) lesions - More frequent, severe compared to age-matched controls
- Diffusion tensor imaging (DTI) - Increased fractional anisotropy (FA) values in posterior limb of internal capsule
- MR elastography (MRE) - Increased stiffness in cerebral, occipital, parietal lobes - Decreased stiffness in periventricular WM
- MR perfusion - ASL: Reduced CBF in periventricular WM, basal ganglia, & thalamus
Nuclear Medicine Findings
- PET
```
- F-18 FDG PET shows decreased regional cerebral metabolism
```
- SPECT: Cerebral blood flow decreased in patients with NPH
- In-111 DTPA cisternography - Prominent ventricular activity with no flow over convexity at 24-48 hours - High false-positive rate
Other Modality Findings
- Phase-contrast cine MR - Cardiac-gated CSF flow studies through aqueduct - Hyperdynamic CSF flow in both systole & diastole - Net CSF flow direction caudocranial, reverse of normal - Aqueduct stroke volume (ASV) > 42 μL - Lack of correlation between ASV & symptom severity
- ICP monitoring: Wave amplitude > 9-mm Hg correlates with post shunt cognitive improvement

Imaging Recommendations

Best imaging tool

- MR with CSF flow studies
- CT helpful

DIFFERENTIAL DIAGNOSIS

Normal Aging Brain
- Thin, periventricular high-signal rim is normal
- Few/no WM hyperintensities
- Proportionately enlarged ventricles & subarachnoid spaces
Alzheimer Disease
- Dementia out of proportion to gait disturbance
- Large parahippocampal fissures, small hippocampi, sulcal enlargement
Multiinfarct Dementia
- Multiple infarcts on imaging
Subcortical Arteriosclerotic Encephalopathy (Binswanger Disease)
- Irreversible ischemic degeneration of periventricular & deep WM
- MR shows extensive periventricular & deep WM hyperintensities, enlarged ventricles

PATHOLOGY

General Features

Etiology

- Pathogenesis of idiopathic NPH (iNPH)****poorly understood & controversial
- Reduced CBF, altered CSF resorption without increased CSF pressure
        - Brain expands in systole, causes CSF displacement
        - Loss of parenchymal compliance, altered viscoelastic properties of ventricular wall
        - Increased interstitial fluid (ISF), pulsation pressure directed toward ventricles, water hammer effect
        - May be further complicated by microangiopathy (including venous compromise), atrophy
- Vascular etiology
        - Altered arterial hemodynamics
        - Cortical venous dysfunction, impairs CSF absorption
- Imbalance between CSF & ISF
        - Excess ISF, reversing ISF flow, impaired removal of neurotoxic compounds (β-amyloid & tau)
- Glymphatic system 
        - Facilitates brain fluid clearance & waste removal during sleep
        - Studies implicated impaired glymphatic function in both Alzheimer disease (AD) & iNPH
- Secondary NPH (**sNPH**): Subarachnoid hemorrhage, meningitis, neurosurgery, or head trauma

Microscopic Features
- Arachnoid fibrosis (50%)
- Periventricular tissue: Disruption of ependyma, edema, neuronal degeneration, & gliosis
- Cerebral parenchyma: Almost 50% show no significant pathology - 20% neurofibrillary tangles, other AD changes - 10% arteriosclerosis, ischemic encephalomalacia

CLINICAL ISSUES

Presentation

Most common signs/symptoms

- Heterogeneous syndrome (classic clinical triad = dementia, gait disorder, urinary incontinence)
- Gait disorder: Disturbed postural & locomotor reflexes in absence of primary sensorimotor deficits
- Bladder dysfunction: Urinary urgency with difficulty inhibiting bladder emptying
- Dementia: Apathy or amotivation, daytime sleepiness, psychomotor slowing

Clinical profile
```
- Reversible cause of dementia
```
Confirmed iNPH, possible iNPH & probable iNPH based on clinical findings, imaging, response to high-volume lumbar tap

Demographics

Age

- Average onset: 70 years
- Idiopathic form of NPH tends to present in elderly
- Patients with chronic communicating hydrocephalus due to prior known insult tend to present at earlier age

Sex
```
- M = F
```
Ethnicity
```
- No ethnic predilection
```

Epidemiology

- Accounts for ~ 5-6% of dementias
- Reported prevalence 0.5-3.0% in elderly population

Natural History & Prognosis
- Continuing cognitive & motor decline, akinetic mutism, & eventual death
- Potentially reversible cause of dementia when shunted
Treatment
- Presurgical confirmatory tests - Tap test (large-volume lumbar puncture) - To assess patient's response to CSF removal - Remove 30-50 mL of CSF - Gait & cognition evaluated before LP & 3-4 hours after LP - High positive predictive value (73-100%) - Drainage of CSF via spinal catheter (external lumbar drainage) - Lumbar catheter placed, CSF removal (10 mL/h) for 2-3 days - Gait & cognition evaluated before & after - Infusion testing - 2 LP needles in lumbar subarachnoid space: 1 connected to infusion pump to infuse artificial CSF, 1 to closed-pressure recording device - CSF outflow resistance (Rουτ) & conductance calculated - Rουτ 8-18 mm Hg/mL/min associated with favorable shunt outcomes - 1-2 hours to complete, needs specialized equipment
- CSF diversion surgery - Shunt surgery indicated for patients who respond to CSF drainage or have CSF hydrodynamic variables consistent with NPH - Endoscopic third ventriculostomy (ETV) - Has not been favorable for treatment of iNPH - Predictors of positive response to shunting remains elusive - Gait disturbance is clinical symptom most likely to respond to surgery

DIAGNOSTIC CHECKLIST

Consider
- Whether ventricular dilation is solely due to atrophy
- Diagnostic challenge = identify shunt-responsive NPH

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References

Selected References

Images

Selected Images

Sagittal T1 MR shows large lateral ventricles , thinning of the corpus callosum , and a relatively normal 4th ventricle in a patient with iNPH.

Axial CECT demonstrates typical findings suggestive of iNPH. There is enlargement of the lateral ventricles and sylvian fissures out of proportion to the amount of general sulcal enlargement. The frontal horns show a characteristic rounded appearance. Periventricular hypodensities could reflect interstitial migration of CSF.

Axial T2 MR in a patient with NPH demonstrates lateral ventricular enlargement and disproportionately enlarged sylvian fissure (DESH). Evans index, which is the ratio of the maximum width of the frontal horns to the maximum internal diameter of the skull at the same level, measures 0.38. Normal Evans index is < 0.3.

Coronal T2 MR in a patient with NPH shows reduced callosal angle (71°). The callosal angle is measured at the level of the posterior commissure and a normal value is between 100-120°.

Sagittal T1 MR demonstrates the cingulate sulcus sign in a patient with NPH with narrowing of the posterior 1/2 of the cingulate sulcus as compared with the anterior .

Axial FLAIR MR in the same patient demonstrates disproportionately enlarged subarachnoid spaces , consistent with DESH, and narrowing of the sulci and subarachnoid spaces over the high convexity parasagittal frontoparietal regions with a tight interhemispheric fissure .

Sagittal T1 MR in a patient with NPH demonstrates focal bulging of the roof of the lateral ventricles , which has been recently described.

Twenty-four hour multiplanar In-111 DTPA cisternography in a patient with NPH shows radiotracer in the lateral ventricles with lack of activity over the convexity . Normally, there should be radiotracer movement over the convexities at 24 hours. (Courtesy C. Singh, MD and A. Ali, MD.)

Axial T2 MR in 65 year old with NPH shows dilated temporal horns and low-signal flow void in the aqueduct caused by hyperdynamic flow of CSF.

Axial phase-contrast cine MR CSF flow study shows increased velocity of CSF through the dilated aqueduct . There is more hyperdynamic flow through the aqueduct than the cisterns, where no high-velocity signal change is seen. Flow is incidentally noted in the posterior cerebral arteries .

Additional Images

Axial NECT shows ventriculomegaly with rounded frontal horns out of proportion to sulcal enlargement.

Axial T2WI MR shows ventricles dilated out of proportion to sulcal enlargement. Periventricular deep white matter lesions are also present.

Axial T2WI MR shows ventriculomegaly.

Sagittal T1WI MR in the same patient shows an accentuated aqueductal flow void .

Axial T2WI MR shows enlarged ventricles with rounded frontal horns.

Axial FLAIR MR in the same patient shows ventriculomegaly out of proportion to sulcal enlargement.

Axial CECT shows symmetric dilatation of the ventricles and sylvian fissures out of proportion to sulcal enlargement. Frontal and occipital periventricular hypodensities suggest transependymal CSF flow.

Axial CECT in the same patient shows symmetric dilatation of the ventricles and sylvian fissures out of proportion to sulcal enlargement. Frontal and occipital periventricular hypodensities are also present.

Axial T2WI MR shows a typical case of normal pressure hydrocephalus. There is enlargement of the lateral ventricles with no sulcal enlargement. The frontal horns show a typical rounded configuration.

Axial T2WI MR shows dilated temporal horns out of proportion to the sulcal prominence. Notice the low-signal flow void in the aqueduct caused by hyperdynamic flow of CSF.

Sagittal T1WI MR shows enlargement of the 3rd and lateral ventricles. The infundibular recess is enlarged and bulges downward. Note mild thinning of the corpus callosum .

Axial FLAIR MR shows enlarged ventricles out of proportion to the sulcal enlargement. Notice that periventricular hyperintensity is also present .

Axial T2WI MR in the same patient shows dilated ventricles. Normal pressure hydrocephalus accounts for ~ 5-6% of all dementias. The classic Hakim triad of dementia, gait apraxia, and urinary incontinence is present in a minority of patients.

Axial NECT shows large ventricles out of proportion to the sulcal prominence with a rounded appearance of the frontal horns .

Axial T2WI MR in the same patient shows ventriculomegaly. The patient presented with the classic clinical triad of NPH: Dementia, gait apraxia, and urinary incontinence. One treatment option is ventricular shunting. The response to shunting is variable.

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KEY FACTS

Terminology

Imaging

Top Differential Diagnoses

Pathology

Clinical Issues

Diagnostic Checklist

TERMINOLOGY

Abbreviations

Synonyms

Definitions

IMAGING

General Features

Best diagnostic clue

Location

Size

Morphology

CT Findings

NECT

MR Findings

Nuclear Medicine Findings

PET

Other Modality Findings

Imaging Recommendations

Best imaging tool

DIFFERENTIAL DIAGNOSIS

PATHOLOGY

General Features

Etiology

Microscopic Features

CLINICAL ISSUES

Presentation

Most common signs/symptoms

Clinical profile

Demographics

Age

Sex

Ethnicity

Epidemiology

Natural History & Prognosis

Treatment

DIAGNOSTIC CHECKLIST

Consider

References

Selected References

Images

Selected Images

Additional Images

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