The role of diffusion tensor imaging and fractional anisotropy in the evaluation of patients with idiopathic normal pressure hydrocephalus: a literature review

Abstract

<jats:sec> <jats:title>OBJECTIVE</jats:title> <jats:p>Diffusion tensor imaging (DTI) for the assessment of fractional anisotropy (FA) and involving measurements of mean diffusivity (MD) and apparent diffusion coefficient (ADC) represents a novel, MRI-based, noninvasive technique that may delineate microstructural changes in cerebral white matter (WM). For example, DTI may be used for the diagnosis and differentiation of idiopathic normal pressure hydrocephalus (iNPH) from other neurodegenerative diseases with similar imaging findings and clinical symptoms and signs. The goal of the current study was to identify and analyze recently published series on the use of DTI as a diagnostic tool. Moreover, the authors also explored the utility of DTI in identifying patients with iNPH who could be managed by surgical intervention.</jats:p></jats:sec> <jats:sec> <jats:title>METHODS</jats:title> <jats:p>The authors performed a literature search of the PubMed database by using any possible combinations of the following terms: “Alzheimer's disease,” “brain,” “cerebrospinal fluid,” “CSF,” “diffusion tensor imaging,” “DTI,” “hydrocephalus,” “idiopathic,” “magnetic resonance imaging,” “normal pressure,” “Parkinson's disease,” and “shunting.” Moreover, all reference lists from the retrieved articles were reviewed to identify any additional pertinent articles.</jats:p></jats:sec> <jats:sec> <jats:title>RESULTS</jats:title> <jats:p>The literature search retrieved 19 studies in which DTI was used for the identification and differentiation of iNPH from other neurodegenerative diseases. The DTI protocols involved different approaches, such as region of interest (ROI) methods, tract-based spatial statistics, voxel-based analysis, and delta-ADC analysis. The most studied anatomical regions were the periventricular WM areas, such as the internal capsule (IC), the corticospinal tract (CST), and the corpus callosum (CC). Patients with iNPH had significantly higher MD in the periventricular WM areas of the CST and the CC than had healthy controls. In addition, FA and ADCs were significantly higher in the CST of iNPH patients than in any other patients with other neurodegenerative diseases. Gait abnormalities of iNPH patients were statistically significantly and negatively correlated with FA in the CST and the minor forceps. Fractional anisotropy had a sensitivity of 94% and a specificity of 80% for diagnosing iNPH. Furthermore, FA and MD values in the CST, the IC, the anterior thalamic region, the fornix, and the hippocampus regions could help differentiate iNPH from Alzheimer or Parkinson disease. Interestingly, CSF drainage or ventriculoperitoneal shunting significantly modified FA and ADCs in iNPH patients whose condition clinically responded to these maneuvers.</jats:p></jats:sec> <jats:sec> <jats:title>CONCLUSIONS</jats:title> <jats:p>Measurements of FA and MD significantly contribute to the detection of axonal loss and gliosis in the periventricular WM areas in patients with iNPH. Diffusion tensor imaging may also represent a valuable noninvasive method for differentiating iNPH from other neurodegenerative diseases. Moreover, DTI can detect dynamic changes in the WM tracts after lumbar drainage or shunting procedures and could help identify iNPH patients who may benefit from surgical intervention.</jats:p></jats:sec>

Neuroimaging in Dementia

“…264 DTI is now being studied to further elucidate the role of WM disease in NPH, 265 and initial results suggest that it may assist with differential diagnosis. [266][267][268][269] Other advanced MRI techniques have been proposed together with DTI to go beyond the limits of structural imaging to help diagnose iNPH more accurately. New CSF quantification techniques such as Time-SLIP sequences are being investigated to gain better insight into CSF flow behavior in NPH.…”

Corticospinal excitability in idiopathic normal pressure hydrocephalus: a transcranial magnetic stimulation study

“…Unexpectedly, the nTMS responses did not correlate with the GPT or gait measurements. TMS induces a direct activation of the corticospinal pathways, and therefore, it could partially bypass the regulatory premotor cortex and the extrapyramidal tracts including the thalamus and the basal ganglia which all are related to the pathophysiology and the motor symptoms of iNPH [49,50]. Therefore, the lack of correlation between some TMS responses and the motor parameters may result from a more complex disturbance in the extrapyramidal pathways, which cannot be extensively evaluated by TMS.…”

Long-term effects of radiation therapy on white matter of the corpus callosum: a diffusion tensor imaging study in children

“…Increased intracranial pressure, ventriculomegaly, hydrocephalus and treatment with shunting could also impact the white matter integrity [44-46]. However, our groups were balanced to minimize potential effects.…”