Diagnostic Approach for Normal Pressure Hydrocephalus
MRI of the brain without IV contrast is the first-line imaging test for suspected NPH, as it provides superior detection of characteristic features including ventriculomegaly, narrowed posterior callosal angle, effaced sulci along high convexities with widened sylvian fissures (DESH pattern), periventricular white matter changes, and cerebral aqueduct flow void. 1, 2
Clinical Recognition
The classic triad develops sequentially, not simultaneously:
- Gait disturbance appears first and is typically the most prominent feature, characterized by slow, wide-based, magnetic gait with difficulty initiating steps 1, 3
- Urinary urgency or incontinence develops as the second manifestation 1, 2
- Cognitive impairment with frontal-subcortical pattern (executive dysfunction, psychomotor slowing) appears later in the disease course 1, 2
The complete triad is not required for diagnosis or treatment consideration—many patients present with incomplete manifestations in 25-50% of cases. 4, 3
Initial Diagnostic Workup
Neuroimaging
MRI brain without contrast is the preferred initial test because CT cannot detect the cerebral aqueduct flow void and may miss small obstructing lesions that would indicate noncommunicating hydrocephalus rather than NPH. 1, 2
Key MRI findings to identify:
- Ventriculomegaly disproportionate to cerebral atrophy 1
- Narrowed posterior callosal angle 1
- Effaced sulci at high convexities with widened sylvian fissures (DESH pattern) 1
- Periventricular white matter hyperintensities 1
- Cerebral aqueduct flow void 1
If MRI is contraindicated (pacemaker, severe claustrophobia), CT head without contrast can identify ventriculomegaly, narrowed callosal angle, and sulcal effacement, though with lower sensitivity for periventricular changes. 1
Laboratory Evaluation
Obtain basic metabolic workup to exclude mimics:
- Complete blood count 2
- Serum electrolytes 2
- Renal and liver function tests 2
- Thyroid function tests 2
- Fasting blood glucose 2
Lumbar Puncture with Opening Pressure
CSF opening pressure should be measured if lumbar puncture is performed, though normal pressure does not exclude NPH. The defining feature is that intracranial pressure remains normal or only mildly elevated despite ventriculomegaly. 1
Predictive Testing for Shunt Response
When imaging supports NPH but the diagnosis remains uncertain or you need to predict surgical benefit:
CSF Tap Test (First-Line Predictive Test)
Remove 30-50 mL of CSF and objectively measure gait speed, cognitive performance, and urinary symptoms before and 2-4 hours after drainage. 4, 5, 3
A positive tap test (objective improvement in gait or cognition) strongly predicts shunt response, but a negative single tap test does NOT exclude benefit from surgery due to low sensitivity. 4, 5
Extended CSF Drainage (When Single Tap Test is Negative)
If the single tap test is negative but clinical suspicion remains high:
- Repeated CSF tap tests (RTT) over 3-5 days increase sensitivity 4
- Continuous lumbar external drainage (LED) for 3-5 days provides the most reliable prediction of shunt response 4, 5
Intracranial Pressure Monitoring (Adjunctive)
B-waves present during >50% of ICP recording time, combined with positive RTT or LED, provides the most reliable prediction of surgical benefit. 4
Role of Other Imaging Modalities
DTPA Cisternography
Shows persistent radiotracer in lateral ventricles and absent activity over convexities on delayed imaging in NPH, but evidence is insufficient to proceed with shunting based on cisternography findings alone. 1
FDG-PET/CT Brain
May show hypometabolism in dorsal striatum with preserved cortical metabolism, helping distinguish NPH from other dementias, but insufficient evidence supports its routine use for NPH diagnosis. 1
Treatment Decision Algorithm
If MRI shows characteristic NPH features AND positive CSF tap test: Refer to neurosurgery for ventriculoperitoneal shunt evaluation 2, 6
If MRI shows characteristic NPH features BUT negative single tap test: Proceed to repeated tap tests or continuous lumbar drainage 4, 5
If extended drainage (RTT or LED) is positive: Strong indication for shunt surgery, as 70-90% of these patients improve clinically 6, 4
If imaging and all CSF drainage tests are negative: NPH is unlikely; pursue alternative diagnoses 4, 5
Critical Pitfalls to Avoid
Three-quarters of patients with NPH severe enough to require treatment have comorbid neurodegenerative disorders (Alzheimer disease, vascular dementia, Parkinson syndromes), making diagnosis challenging. 6, 3 However, any patient showing improvement after CSF drainage deserves therapeutic intervention, even with comorbid conditions. 5
Do not delay diagnosis—approximately 80% of NPH cases remain unrecognized and untreated, and the spontaneous course leads to nursing care dependence in the vast majority of patients. 6 Early treatment with shunt surgery improves outcomes compared to natural disease progression. 6
Cervical stenosis commonly coexists with NPH and may require separate surgical intervention. 3