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Noninvasive biomarkers in normal pressure hydrocephalus: evidence for the role of neuroimaging.

OBJECT
Normal pressure hydrocephalus (NPH) represents a treatable form of dementia. Recent estimates of the incidence of this condition are in the region of 5% of patients with dementia. The symptoms of NPH can vary among individuals and may be confused with those of patients with multi-infarct dementia, dementia of the Alzheimer type, or even Parkinson disease. Traditionally the diagnosis of NPH could only be confirmed postoperatively by a favorable outcome to surgical diversion of CSF. The object of this literature review was to examine the role of structural and functional imaging in providing biomarkers of favorable surgical outcome.


METHODS
A Medline search was undertaken for the years 1980-2006, using the following terms: normal pressure hydrocephalus, adult hydrocephalus, chronic hydrocephalus, imaging, neuroimaging, imaging studies, outcomes, surgical outcomes, prognosis, prognostic value, sensitivity, specificity, positive predictive value, negative predictive value, and accuracy.


RESULTS
The query revealed 16 studies that correlated imaging with surgical outcomes offering accuracy results. Three studies fulfilled the statistical criteria of a biomarker. A dementia Alzheimer-type pattern on SPECT in patients with idiopathic NPH, the presence of CSF flow void on MR imaging, and the N-acetylaspartate/choline ratio in patients with the secondary form are able to predict surgical outcomes with high accuracy.


CONCLUSIONS
There is at present Level A evidence for using MR spectroscopy in patients with secondary NPH, and Level B evidence for using SPECT and phase-contrast MR imaging to select patients with idiopathic NPH for shunt placement. The studies, however, need to be repeated by other groups. The current work should act as a platform to design further studies with larger sample sizes.