Abstract
PurposePatients with idiopathic normal pressure hydrocephalus (iNPH) present white-matter abnormalities. The analytical methods described to date only measure mean diffusion parameter alterations of iNPH-specific brain regions or in a certain fasciculus. This study quantitatively analyzed whether iNPH-tract abnormalities are confined to specific sections or involve entire fibers based on diffusion spectrum imaging (DSI). MethodTwenty-two patients with iNPH and 20 normally aging subjects were included. The 18 main tracts in the brain of each subject were extracted, and the diffusion parameters of 100 equidistant nodes on each fiber were calculated to quantitatively evaluate integrity changes in different regions along these tracts. Two diffusion metrics were measured, i.e., general fractional anisotropy (GFA) and fractional anisotropy (FA). ResultsCompared to normally aging (P < 0.05), in iNPH, the GFA and FA of the left uncinate fasciculus and FA of the bilateral superior longitudinal fasciculus 1 were reduced in areas where the entire fiber was involved (%nodes with significant differences > 90%). Most other fasciculi detected presented GFA or FA alterations limited to specific regions. Increased and decreased GFA or FA co-occurred in different sections of the same fibers, including the corticospinal tract and left thalamic radiation posterior in iNPH. ConclusionsFew iNPH fibers presented diffusion abnormalities involving nearly all tracts. Most fiber abnormalities in iNPH were confined to specific areas, and different parts of the same fasciculus showed diverse diffusion alterations in few cases. This DSI-based tract analysis provided detailed information on iNPH white-matter changes.
Highlights
Idiopathic normal pressure hydrocephalus is a neurological disorder of unknown etiology that can be treated surgically and mainly occurs in elderly individuals [1]. iNPH patients exhibit at least one of the three symptoms of gait disturbance, urinary incontinence, and cognitive impairment [2]
Most fiber abnormalities in iNPH were confined to specific areas, and different parts of the same fasciculus showed diverse diffusion alterations in few cases
Previous studies have suggested the existence of white-matter abnormalities in iNPH, presumably due to factors such as mechanical pressure caused by ventriculomegaly and metabolic disturbances [3,4]
Summary
Idiopathic normal pressure hydrocephalus (iNPH) is a neurological disorder of unknown etiology that can be treated surgically and mainly occurs in elderly individuals [1]. iNPH patients exhibit at least one of the three symptoms of gait disturbance, urinary incontinence, and cognitive impairment [2]. Lumbar puncture shows cerebrospinal fluid (CSF) pressure within the normal range, iNPH mainly manifests as ventricle enlargement on radiological images [1,2]. Previous studies have suggested the existence of white-matter abnormalities in iNPH, presumably due to factors such as mechanical pressure caused by ventriculomegaly and metabolic disturbances [3,4]. White-matter alterations are observed in iNPH, most previously employed analysis methods could only detect changes in average diffusion tensor imaging (DTI) metrics of brain areas-of-interest (such as the periventricular white matter) or in a specific fiber bundle (such as the corticospinal tract) [4,5]. Whether white-matter fiber abnormalities seen in iNPH are confined to specific tract sections or involve the entire fibers remains unclear. Diffusion spectrum imaging (DSI) effectively compensates for the deficiencies of the DTI algorithm and has a higher angular resolution that can precisely show sophisticated cross-winding tracts and fine microstructure white-matter alterations [6,7]
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