Normal pressure hydrocephalus (NPH) remains a controversial entity with often ambiguous imaging findings.
The majority of cases of normal pressure hydrocephalus (NPH) are idiopathic and is referred to as primary NPH. Many causes of secondary NPH exist including 3:
The classical clinical findings of normal pressure hydrocephalus are 1-3:
- urinary incontinence
- intellectual deterioration
- gait disturbances
These can be remembered with the unkind mnemonic Wet, Wacky and Wobbly.
As the name suggests mean CSF opening pressure in patients with NPH is within the normal range (<18 cm H2O or 13 mm Hg) 3.
The underlying cause of NPH remains controversial. One theory is that NPH is an obstructive type of communicating hydrocephalus due to reduced of CSF resorption. A second theory suggests that NPH results from weakening of the ventricular wall due to periventricular white matter ischemic damage 3.
Although CT is able to visualise the anatomical changes of NPH, it is inferior to MRI.
- ventriculomegaly 1-3
- crowding of the gyri at the vertex (with small sulci)
- sylvian fissures out of proportion to sulcal enlargement (which is minimal) and hippocampus and mesial temporal lobe volumes (which are near normal)
- aqueductal flow void
- best seen on T2 spin echo sequences
- favorable outcome if shunt surgery
- periventricular high signal on T2 weighted sequences
- MR spectroscopy : lactate peak in lateral ventricles
- CSF flow studies 3
- increased aqueductal stroke volume
- increased aqueductal peak velocity
- NB : absence of a flow void does not exclude the diagnosis
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Treatment and prognosis
Treatment of normal pressure hydrocephalus, once the diagnosis is established, is with CSF shunting, usually a ventriculoperitoneal shunt (VP shunt). The challenge is identifying those patients which will benefit from shunting. Favourable prognostic factors include 3:
- short duration of presurgical symptoms (less than 6 months)
- onset of gait disturbance before dementia
- temporary symptom relief from a CSF tap test (removal of 40ml of CSF via lumbar puncture)
- absence of significant cerebral vascular disease
- 1. Kitagaki H, Mori E, Ishii K et-al. CSF spaces in idiopathic normal pressure hydrocephalus: morphology and volumetry. AJNR Am J Neuroradiol. 1998;19 (7): 1277-84. AJNR Am J Neuroradiol (abstract) - Pubmed citation
- 2. Holodny AI, Waxman R, George AE et-al. MR differential diagnosis of normal-pressure hydrocephalus and Alzheimer disease: significance of perihippocampal fissures. AJNR Am J Neuroradiol. 1998;19 (5): 813-9. AJNR Am J Neuroradiol (abstract) - Pubmed citation
- 3. Hurley RA, Bradley WG, Latifi HT et-al. Normal pressure hydrocephalus: significance of MRI in a potentially treatable dementia. J Neuropsychiatry Clin Neurosci. 1999;11 (3): 297-300. J Neuropsychiatry Clin Neurosci (full text) - Pubmed citation
Synonyms & Alternative Spellings
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