What is the next step after a CT (Computed Tomography) scan suggests possible Normal Pressure Hydrocephalus (NPH)?

Next Steps After CT Suggests Possible Normal Pressure Hydrocephalus

The next step after a CT scan suggests possible Normal Pressure Hydrocephalus (NPH) should be an MRI of the brain without IV contrast to confirm the diagnosis and evaluate for characteristic features that CT may miss. 1, 2

Diagnostic Confirmation

• MRI without IV contrast is recommended by the American College of Radiology as the preferred imaging modality for NPH due to its superior ability to detect characteristic features compared to CT 3, 2
• MRI can identify key features that CT may miss, including:
  • Cerebral aqueduct flow void (cannot be visualized on CT) 2
  • Periventricular white matter changes (higher sensitivity on MRI) 2
  • Disproportionately enlarged subarachnoid-space hydrocephalus (DESH) pattern 2
  • Ventriculomegaly with Evans' index >0.3 2
  • Narrowed posterior callosal angle (<90°) 2
  • Effaced sulci along high convexities with widened sylvian fissures 3

Clinical Assessment

• Confirm the presence of the clinical triad of NPH symptoms, which typically develop in sequence:
  • Gait disturbance (usually occurs first) 1
  • Urinary incontinence or urgency 1
  • Cognitive impairment (typically frontal-subcortical pattern) 1, 4
• Document the temporal progression of symptoms, as patients typically present late in the disease course due to the slow, gradual onset 5

Laboratory Evaluation

• Complete basic laboratory workup to rule out other causes of cognitive impairment:
  • Complete blood count 1
  • Serum electrolytes 1
  • Renal and liver function tests 1
  • Thyroid function tests 1
  • Fasting blood glucose 1

Supplementary Testing

• After MRI confirmation, perform a high-volume lumbar puncture (tap test) or external lumbar drainage to assess for clinical improvement 4
  • Measure gait performance before and after CSF removal 4
  • Improvement after CSF removal is highly predictive of shunt responsiveness 4
• Consider CSF infusion testing to measure CSF outflow resistance in complex cases 4

Treatment Planning

• Refer patients with positive diagnostic findings and positive response to CSF removal to neurosurgery for ventriculoperitoneal shunt placement evaluation 1, 4
• Properly selected patients have an 80-90% chance of responding to shunt surgery 4

Important Considerations

• NPH is often comorbid with other neurodegenerative diseases (present in 20-57% of NPH patients) 5
• Approximately 75% of patients with NPH severe enough to require treatment also suffer from another neurodegenerative disorder 5, 6
• Early diagnosis and treatment are critical, as untreated NPH typically progresses to dependence on nursing care 6
• The prevalence of NPH is estimated at 3.7% in patients over 65 years of age, making it a potentially reversible cause of dementia that is often underdiagnosed 3, 6

Common Pitfalls to Avoid

• Relying solely on CT findings without MRI confirmation when possible 1
• Failing to perform CSF removal tests to predict shunt responsiveness 4
• Misdiagnosing NPH as another neurodegenerative disorder 1
• Delaying treatment, as early intervention leads to better outcomes 6, 7