ARRS 2022 Abstracts

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ERS3324. Change in Signal Intensity of White Matter as an Aid in Assessment of Response of Normal Pressure Hydrocephalus to VP Shunting
Authors * Denotes Presenting Author
  1. Karthika Ramakrishnan *; Temple University Health System
  2. Konstantin Chernukha; Temple University Health System
Objective:
Dementia is a common denominator for idiopathic normal pressure hydrocephalus (iNPH) and Alzheimer’s disease (AD). Also, iNPH may mask an underlying cerebral atrophy, a known biomarker of AD. Not surprisingly, many patients with iNPH eventually develop AD despite of decrease in ventriculomegaly in response to ventriculoperitoneal shunting (VPS) which may explain why there is usually little, if any, objective improvement in cognition following VPS. We hypothesize that expected decrease (or lack of) in the brain water content after VPS may help to identify those patients with preclinical AD. However, such a decrease in water content may be imperceptible by the human eye. The aim of this study is to validate a noninvasive quantitative method of measurement of water content in the white matter we have proposed.

Materials and Methods:
Retrospective review of 11 patients with NPH (mean age 40.3, 6 females, 5 male) who underwent non-contrast MRI brain prior to and following VPS was performed. Of note, 6 out of 11 patients reported subjectively improved cognition following intervention which was not verified with subsequent testing. To quantify change in water content of white matter, we measured the difference in signal intensity (dSI) between the subcortical white matter and the periventricular white matter on T1, T2 and FLAIR sequences. Representative signal intensities were recorded in the arbitrarily selected regions of interest: the frontal subcortical white matter (Fs), the parietal subcortical white matter (Ps) and the parietal periventricular white matter (Pp). Two dSI values were recorded (averages of values obtained for right and left cerebral hemisphere): dSI1=Pp–Fs and dSI2=Pp-Ps.

Results:
As expected, both dSI1 and dSI2 values decreased after VPS on all three sequences, with statistically significant differences achieved for FLAIR and T2 with means as follows: FLAIR pre-dSI1 68 v post-dSI1 32, p value <0.05; FLAIR pre-dSI2 101 v post-dSI2 38, p value <0.003; T2 pre-dSI1 104 v post-dSI1 45, p value <0.05; T2 pre-dSI2 117 v post-dSI2 67, p value <0.05. T1 pre-dSI1 -234 v post-dSI1-81, p value = ns and T1 pre-dSI2 -45v post-dSI2 -38, p value = ns. Following shunting of iNPH, the observed significant decrease in white matter signal intensity (dSI) on water-sensitive sequences (T2 and FLAIR) reflects an expected decrease in water content, thus proving dSI a reliable quantitative biomarker.

Conclusion:
Quantitative assessment of gradual change in water content between the subcortical and periventricular white matter on routine MRI by the means of dSI may facilitate diagnosis of preclinical dementia at the earlier stage. This study lays the groundwork for future investigations involving the quantification of interstitial cerebral fluid and its implications for evaluating cognitive impairment.