Diffusion tensor imaging profiles reveal specific neural tract distortion in normal pressure hydrocephalus

Abstract

BackgroundThe pathogenesis of normal pressure hydrocephalus (NPH) remains unclear which limits both early diagnosis and prognostication. The responsiveness to intervention of differing, complex and concurrent injury patterns on imaging have not been well-characterized. We used diffusion tensor imaging (DTI) to explore the topography and reversibility of white matter injury in NPH pre- and early after shunting.MethodsTwenty-five participants (sixteen NPH patients and nine healthy controls) underwent DTI, pre-operatively and at two weeks post-intervention in patients. We interrogated 40 datasets to generate a full panel of DTI measures and corroborated findings with plots of isotropy (p) vs. anisotropy (q).ResultsConcurrent examination of DTI measures revealed distinct profiles for NPH patients vs. controls. PQ plots demonstrated that patterns of injury occupied discrete white matter districts. DTI profiles for different white matter tracts showed changes consistent with i) predominant transependymal diffusion with stretch/ compression, ii) oedema with or without stretch/ compression and iii) predominant stretch/ compression. Findings were specific to individual tracts and dependent upon their proximity to the ventricles. At two weeks post-intervention, there was a 6·7% drop in axial diffusivity (p = 0·022) in the posterior limb of the internal capsule, compatible with improvement in stretch/ compression, that preceded any discernible changes in clinical outcome. On PQ plots, the trajectories of the posterior limb of the internal capsule and inferior longitudinal fasciculus suggested attempted ‘round trips’. i.e. return to normality.ConclusionDTI profiling with p:q correlation may offer a non-invasive biomarker of the characteristics of potentially reversible white matter injury.

Diffusion Tensor Imaging of the Superior Thalamic Radiation and Cerebrospinal Fluid Distribution in Idiopathic Normal Pressure Hydrocephalus

“…The effect of iNPH on many WM tracts have been previously explored using variety of DTI techniques. Increased MDs in the periventricular WM have been reported using voxel‐based analysis, tract‐based spatial statistics (TBSS), and ROI analysis . This increase in the MDs may increased diffusion of extracellular water molecules in the major projection bundles near the ventricular system in with iNPH …”

“…Increased MDs in the periventricular WM have been reported using voxel-based analysis, 27 tract-based spatial statistics (TBSS), 28,29 and ROI analysis. 30,31 This increase in the MDs may increased diffusion of extracellular water molecules in the major projection bundles near the ventricular system in with iNPH. 32 iNPH effect on FA value of surrounding WM pathways is more heterogeneous across the studies.…”

“…28 ROI-based analyses showed that FA values of the CST were increased in iNPH patients compared to healthy controls in one study 30 and decreased in another compared to normal controls and Parkinson's disease patients. 31,33 It was proposed that the increased FA value of the CST is mainly due to increase in axial diffusivity and hypothesized that the stretching and compression effect of the enlarging ventricles leads to reduced tortuosity and increased coherence of the WM tracts leads to increased diffusivity of water parallel to these fibers. 28 Additionally, axonal damage and degeneration of the crossing fibers were thought to be playing an additional role in the increased FA values in the CST.…”

Frontal Behavior Syndromes in Idiopathic Normal Pressure Hydrocephalus as a Function of Alzheimer’s Disease Biomarker Status

“…Frontal Behavior Syndromes in iNPH ± AD inferior fronto-occipital/uncinate tracts (Keong et al, 2017). Dopaminergic abnormalities have also been evidenced in asymmetric changes in binding potential of pre-synaptic and post-synaptic radiotracers in the dorsal putamen (Ouchi et al, 2007).…”

Diffusion tensor magnetic resonance imaging of the optic nerves in pediatric hydrocephalus

“…11 Previous studies have used DTI to examine white matter in adults with idiopathic hydrocephalus and found significant differences in MD and FA, 7 which were relieved after normalization of ICP. 9,12 However, studies of pediatric hydrocephalus have largely focused on the corpus callosum, anterior and posterior limbs of the internal capsule, corticospinal tract, and superior and inferior longitudinal fasciculus. 14 No studies have examined diffusion tensor-based microstructural changes of the optic nerve in children presenting with obstructive hydrocephalus.…”