Normal Pressure Hydrocephalus - Diagnosis

Diagnosis

Diagnosis of NPH is usually first led by brain imaging, either CT or MRI, to rule out any mass lesions in the brain. This is then followed by lumbar puncture and evaluation of clinical response to removal of CSF. This can be followed by continuous external lumbar CSF drainage during 3 or 4 days.

• CT scan may show enlarged ventricles without convolutional atrophy.

• MRI may show some degree of transependymal migration of CSF surrounding the ventricles on T2/FLAIR sequence. Imaging however cannot differentiate between pathologies with similar clinical picture like Alzheimer's dementia, vascular dementia or Parkinson's disease.

• Following imaging, Lumbar puncture is usually the first step in diagnosis and the CSF opening pressure is measured carefully. In most cases, CSF pressure is usually above 155 mmH₂O. Clinical improvement after removal of CSF (30 mL or more) has a high predictive value for subsequent success with shunting. This is called the "lumbar tap test" or Miller Fisher test. On the contrary, a "negative" test has a very low predictive accuracy, as many patients may improve after a shunt in spite of lack of improvement after CSF removal.

• Infusion test is a test that may have higher sensitivity and specificity than a lumbar puncture, but is not performed in most centers. The outflow conductance (Cout) of the cerebrospinal fluid (CSF) system is a parameter considered by some centers to be predictive in selection for hydrocephalus surgery. Cout can be determined through an infusion test. This is not a test that is normally performed prior to shunting, but may become more accepted.

• In some centers, External lumbar drainage has been shown to have the highest sensitivity and specificity with regards to predicting a successful outcome following surgery.