MR Elastography Demonstrates Increased Brain Stiffness in Normal Pressure Hydrocephalus

Abstract

Introduction Normal pressure hydrocephalus (NPH) is a reversible neurologic disorder characterized by a triad of cognitive impairment, gait abnormality and urinary incontinence that is commonly treated with ventriculoperitoneal shunt placement. However, there are multiple overlapping symptoms which often make it difficult to differentiate NPH from other types of dementia and improved diagnostic techniques would help patient management. MR elastography (MRE) is a novel diagnostic tool that could potentially identify patients with NPH. The purpose of this study was to assess brain stiffness changes in NPH patients compared with age- and sex-matched cognitively normal individuals. Methods MRE was performed on 10 NPH patients and 21 age- and sex-matched volunteers with no known neurologic disorders. Image acquisition was conducted on a 3T MRI scanner. Shear waves with 60Hz vibration frequency were transmitted into the brain by a pillow-like passive driver. A novel postprocessing technique resistant to noise and edge artifacts was implemented to determine regional brain stiffness. The Wilcoxon rank sum test and linear regression were used for statistical analysis. Results A significant increase in stiffness was observed in the cerebrum (p = 0.001), occipital lobe (p = 0.0002), parietal lobe (p= 0.001), and the temporal lobe (p = 0.02) in the NPH group compared with normal controls. However, no significant difference was noted in other regions of the brain including the frontal lobe (p = 0.07), deep gray and white matter (p = 0.43), or the cerebellum (p = 0.20). Conclusion This study demonstrates increased brain stiffness in NPH patients compared to age- and sex-matched normal controls which motivates future studies investigating the use of MRE for NPH diagnosis and efficacy of shunt therapy.

Clinical Correlation of Abnormal Findings on Magnetic Resonance Elastography in Idiopathic Normal Pressure Hydrocephalus

“…15,36 The Streitberger protocol is based on three adjacent 6mm slices, which are subsequently integrated into two regions—global and periventricular—both of which were found to be less stiff in iNPH. By contrast, our protocol is driven by 3mm full-volume data sets segmented into anatomical regions using a warped lobar atlas.…”

“…Voxels with significant CSF contributions were masked to further ensure that recorded stiffness values accurately reflected changes in parenchymal tissue, rather than propagation of waveforms in spinal fluid spaces. 8,15–18 MRE image acquisition and processing protocols have been previously described. 16,17,19 , which we have previously demonstrated decreases variation in measurements of brain stiffness.…”

Magnetic Resonance Elastography Demonstrating Low Brain Stiffness in a Patient with Low-Pressure Hydrocephalus: Case Report

“…A more recent work by Fattahi et al [32] instead found a slight increase in cerebrum stiffness of approximately 3.5% in 10 patients with NPH using MRE at 60 Hz. Here we report an extremely low brain stiffness of 1.62 kPa, which is approximately 46% lower than a normal brain stiffness of 3.0 kPa, and a much larger change in properties than previously reported for NPH.…”

Advanced Neuroimaging Techniques in Pediatric Hydrocephalus

“…MR elastography is a noninvasive study that evaluates the mechanical properties of tissue in vivo, and it has been shown in prior studies that pressure changes that cause changes in tissue elasticity can be detected by MR elastography [85,86] . Fattahi et al [84] reported their study of MR elastography in adult patients with normal pressure hydrocephalus, which showed that these patients had increased brain stiffness when compared with age-and sex-matched controls. These results suggest that MR elastography can perhaps serve as a novel diagnostic and surveillance tool in pediatric hydrocephalus.…”

“…Further developments are also being made in various advance MR techniques such as MR elastography for the assessment of brain and ventricular compliance or stiffness in patients with hydrocephalus [84] . MR elastography is a noninvasive study that evaluates the mechanical properties of tissue in vivo, and it has been shown in prior studies that pressure changes that cause changes in tissue elasticity can be detected by MR elastography [85,86] .…”