Normal Pressure Hydrocephalus
05 November 2004
Utility of Hakimís triad
most likely to improve after shunting
magnetic phenomenon, postural instability, short stepped shuffling gait. Hyperreflexia.
less likely to respond to shunting
subcortical / frontal impairment: trail making test
urgency is common
Ventricular enlargement out of proportion to cerebral atrophy, rounded frontal horns, enlarged temporal horns without hippocampal atrophy
Miller Fisher tap test
Easy, rapid, cheap
High rate of false negative
Pre & post LP - neuropsych for frontal lobe function
- gait: ambulation velocity, up & go test, postural stability.
For more information, see section on Miller Fisher Test.
Flow void in aqueduct
White matter hyperintensities
Continuous Lumbar Drain
150-200 ml/d drainage for 3 days
complications: radicular inflammation, meningitis
sensitivity 97%, specificity 60%
SPECT Cerebral blood flow
No good correlate between changes in cerebral blood flow and outcome after shunting
Even pre & post LP will not provide helpful pre-op prediction
A waves & excess B waves correlates well with good outcome post surgery
Can be done in conjunction with Diamox challenge test
ICP <10 mm Hg is normal
Severe or uncontrolled when ICP>40 mm Hg for >15 minutes
A waves or plateau waves
Large increases above baseline to max 50-100 mm Hg for 5-20 min
Associated with ICP>20 & with neurological symptoms related to pressure
As baseline ICP increases, A waves increase in magnitude & frequency
Indicate intracranial spatial compensation has been exhausted
Associated with increased cerebral blood volume and decreased cerebral blood flow
Rhythmic oscillations about every minute with amplitude max of 50 mm Hg
Partly related to depression of consciousness
Often found in association with periodic breathing
May disappear with mechanical ventilation
Rhythmic oscillations up to 20 mm Hg with frequency of 4-8/minute
Associated with Traube-Herring-Mayer blood pressure waves.
A waves important, B & C waves of little usefulness in patient management.
Lumbar infusion tests +/- computer modeling
Measures of resistance or conductance
Mixed results in predicting outcome
Shunt responsiveness (50-70 % accuracy)
known cause of hydrocephalus
predominance of gait disorders
CT showing hydrocephalus
A waves & excess B waves
Substantial cortical atrophy
Extensive white matter involvement
When doubts persist after clinical, CT, MRI & tap test; perform lumbar drainage and to shunt only if unequivocal clinical improvement.
Therapeutic nihilism vs shunt every patient: which is best test?
N=166 consecutive patients with clinical & CT criteria shunted
36% overall improvement
21% substantial improvement
Acute complication rate post shunt: 28%
Death or severe residual morbidity 7%
Cumulative complication rate post shunt: 5%/yr
Conclusion: more harm than good is done by subjecting most NPH patients to a shunt procedure.
Vanneste J et al Shunting normal pressure hydrocephalus: Do the benefits outweigh the risks? A multicentre study and literature review. Neurology 1992; 42:55-59.