What is the diagnosis and treatment of normal pressure hydrocephalus (NPH)?

Normal Pressure Hydrocephalus Diagnosis

MRI head without IV contrast is the preferred initial imaging modality for NPH diagnosis, and patients demonstrating clinical improvement after large-volume lumbar puncture or external lumbar drainage should proceed to ventriculoperitoneal shunt surgery, which has an 80-90% success rate in properly selected patients. 1

Clinical Presentation

The cardinal clinical features follow a characteristic temporal pattern:

• Gait disturbance appears first in approximately 70% of NPH patients, characterized by a hypokinetic pattern where feet appear "glued to the floor" or "magnetic" 1
• Cognitive impairment develops later in the disease course 2
• Urinary incontinence completes the classic triad 3, 4
• Important caveat: 25-50% of cases present with atypical or incomplete manifestations, complicating diagnosis 3
• Three-quarters of patients with NPH severe enough to require treatment have coexisting neurodegenerative disorders, making pure clinical diagnosis insufficient 4

Diagnostic Imaging

MRI Findings (First-Line)

The American College of Radiology recommends MRI without IV contrast as the preferred modality because it identifies multiple critical features that CT cannot detect 1, 2:

Required imaging criteria for probable NPH 1:

• Ventricular enlargement (Evans index >0.3) not entirely attributable to cerebral atrophy or congenital enlargement 2, 5
• No macroscopic obstruction of CSF flow 1

Supportive MRI features 1, 2, 5:

• Enlargement of temporal horns disproportionate to hippocampal atrophy
• Callosal angle <90° (measured between 40-90°)
• Cerebral aqueduct flow void (critical finding associated with good shunt response, not visible on CT) 1, 2
• Periventricular white matter changes (higher sensitivity on MRI than CT) 2
• Disproportionately enlarged subarachnoid-space hydrocephalus (DESH) pattern: tight high-convexity sulci, enlarged Sylvian fissures, and ventriculomegaly 2, 5
• Rounded frontal horns with ballooning 5
• Corpus callosum thinning and elevation 5

CT Head Without Contrast (Alternative)

Use CT only when MRI is unavailable or contraindicated 2:

• Can identify ventriculomegaly, narrowed callosal angle, effaced sulci, and widened Sylvian fissures 2
• Major limitation: Cannot detect cerebral aqueduct flow void and has lower sensitivity for periventricular white matter changes 2
• May miss small obstructing lesions 2

Predictive Testing for Shunt Responsiveness

After imaging confirms NPH, proceed with CSF drainage testing to predict surgical outcome 1, 3:

CSF Tap Test Protocol

• Single large-volume lumbar puncture (CSF tap test) has low sensitivity and cannot exclude patients from surgery if negative 3
• Continuous external lumbar drainage (LED) for 3-5 days removing at least 150 mL/day provides the highest sensitivity (50-100%) and positive predictive value (80-100%) 3, 5
• Clinical improvement following CSF drainage reliably identifies patients likely to respond to shunt surgery 1

Advanced MRI Predictive Testing

• Elevated aqueductal CSF stroke volume measured by phase-contrast MRI demonstrates high positive predictive value (up to 100% in some studies) for shunt responsiveness 1, 6
• Hyperdynamic CSF flow through the aqueduct strongly predicts good surgical outcome 6

Treatment Decision Algorithm

For patients with supportive imaging findings 1, 2:

1. Confirm MRI shows ventriculomegaly with Evans index >0.3 plus at least one supportive feature (callosal angle <90°, temporal horn enlargement, aqueductal flow void)
2. Perform large-volume lumbar puncture or 3-5 day external lumbar drainage
3. If clinical improvement occurs: Proceed to ventriculoperitoneal shunt placement (80-90% response rate, 6% serious complication rate) 1
4. If no improvement but high clinical suspicion: Consider phase-contrast MRI to measure aqueductal stroke volume 1, 6

For patients with conflicting findings 7:

• Non-supportive MRI but positive CSF tap test: Any patient with improvement after CSF drainage deserves therapeutic intervention 7
• Supportive MRI but negative single tap test: Proceed to extended external lumbar drainage before excluding shunt candidacy 3

Critical Pitfalls

• Do not rely on CSF pressure measurement: CSF pressure can be normal in NPH patients, and normal pressure should not exclude the diagnosis 3, 4
• Do not use radionuclide cisternography alone: Evidence is insufficient to proceed with shunting based solely on cisternography findings 2
• Recognize the "two-hit" pathophysiology: Many NPH patients had benign external hydrocephalus in infancy (large heads) followed by deep white matter ischemia in late adulthood 6
• Early treatment is essential: The spontaneous course of untreated NPH leads to nursing care dependence in the vast majority of patients, and approximately 80% of cases remain unrecognized 4