What are the next steps after a CT scan suggests possible Normal Pressure Hydrocephalus (NPH)?

Management of Suspected Normal Pressure Hydrocephalus After CT Scan

After a CT scan suggests possible Normal Pressure Hydrocephalus (NPH), the next step should be an MRI without IV contrast to confirm the diagnosis, followed by a high-volume lumbar puncture (tap test) to assess potential shunt responsiveness. 1, 2

Diagnostic Confirmation with MRI

• MRI without IV contrast is the preferred imaging modality for confirming NPH diagnosis due to its superior ability to detect characteristic features that CT may miss 2, 3

• Key MRI findings to look for include:

  • Ventriculomegaly (Evans' index >0.3) 3
  • Narrowed posterior callosal angle (<90°) 3
  • Effaced sulci along high convexities with widened sylvian fissures (DESH pattern) 3
  • Periventricular white matter changes 1
  • Cerebral aqueduct flow void (cannot be visualized on CT) 3

• If MRI is contraindicated or unavailable, CT head without IV contrast can be used as an alternative, though it has lower sensitivity for some NPH features 1, 3

Clinical Assessment

• Confirm the presence of the classic NPH triad, noting that symptoms typically develop in sequence: 4, 5

  • Gait disturbance (cardinal and earliest sign) - characterized by shuffling, magnetic or "glued to the floor" appearance 5
  • Urinary incontinence or urgency 1
  • Cognitive impairment (typically frontal-subcortical pattern) 4

• Assess for comorbid neurodegenerative conditions, as approximately 75% of NPH patients requiring treatment also have another neurodegenerative disorder 6

Functional Testing

• Perform a high-volume lumbar puncture (tap test) to remove approximately 30-50 ml of CSF 5, 7

  • Document gait performance before and after the procedure 7
  • A positive response (temporary improvement in gait) strongly suggests shunt responsiveness 5, 7

• For inconclusive tap test results, consider:

  • Extended external lumbar drainage (ELD) over 72 hours 7
  • CSF infusion testing to measure CSF outflow resistance 7

Laboratory Evaluation

• Complete basic laboratory workup to rule out other causes of cognitive impairment: 2
  • Complete blood count
  • Serum electrolytes
  • Renal and liver function tests
  • Thyroid function tests
  • Fasting blood glucose

Treatment Planning

• Refer patients with positive diagnostic findings to neurosurgery for ventriculoperitoneal shunt placement evaluation 1, 7
• Modern treatment approaches lead to clinical improvement in 70-90% of appropriately selected patients 6
• Early intervention is associated with better outcomes 6, 7

Common Pitfalls to Avoid

• Misdiagnosing NPH as another neurodegenerative disorder - NPH is potentially reversible with proper treatment 4, 6
• Relying solely on CT findings without MRI confirmation when possible 1, 3
• Failing to perform functional testing (tap test) to assess shunt responsiveness 7
• Delaying treatment, as untreated NPH typically progresses to nursing care dependence 6
• Overlooking comorbid neurodegenerative conditions that may affect treatment response 6, 8