Diffusion tensor imaging in idiopathic normal pressure hydrocephalus: clinical and CSF flowmetry correlations

Diffusion tensor imaging is a magnetic resonance technique that provides information about the orientation and anisotropy of the white matter tracts. The aim of this study was to analyse diffusion tensor imaging quantitative parameters in idiopathic normal pressure hydrocephalus patients, in order to determine whether this method could correlate to clinical scores and cerebrospinal fluid flowmetry data.

Fifteen consecutive patients with idiopathic normal pressure hydrocephalus and 15 age-matched controls underwent cerebrospinal fluid flowmetry and diffusion tensor imaging using a 1.5 Tesla system. Fractional anisotropy, mean diffusivity, axial diffusivity and radial diffusivity values were calculated using region of interest atlas-based tract-mapping in nine cerebral areas and compared among the two groups. In addition, for idiopathic normal pressure hydrocephalus patients, diffusion tensor imaging parameters were correlated to clinical scores (mini mental state examination and frontal assessment battery) and cerebrospinal fluid flowmetry data.

Mean fractional anisotropy was significantly lower for the idiopathic normal pressure hydrocephalus group than for the control group in the forceps minor and motor cortex; the idiopathic normal pressure hydrocephalus group had significantly higher mean axial diffusivity for the genu of the corpus callosum and forceps minor. We did not find significant correlation between diffusion tensor imaging parameters and cerebrospinal fluid flowmetry and mini mental state examination, while we observed a correlation between forceps minor fractional anisotropy and frontal assessment battery; no correlation between flowmetry and clinical scores was found.

Our findings suggest that diffusion tensor imaging provides a non-invasive biomarker of white matter changes in idiopathic normal pressure hydrocephalus patients. Forceps minor is the best site to analyse. As diffusion tensor imaging offers a better correlation to clinical status than cerebrospinal fluid flowmetry, it should be included in the routine idiopathic normal pressure hydrocephalus protocol.