Hydrocephalic Dementia: Revisited with Multimodality Imaging and toward a Unified Imaging Approach.

Overlap of normal pressure hydrocephalus (NPH) and pathology proven cases of dementia is known. The objective of this paper is to correlate both the clinical and multimodality imaging findings in patients with imaging diagnosis NPH and give a hypothesis for association of clinical findings.  This is a retrospective observational analysis of 13 cases patients who were referred to molecular imaging center for imaging in 2016 to 2019, and they were divided into four groups based on structural imaging findings. Group 1 had magnetic resonance imaging (MRI) findings of diffuse effacement of sulcal spaces (DESH) and flow void, whereas Group 4 had none of these two. Group 3 had MRI findings of DESH but no flow void, and Group 2 had flow void but no DESH. Clinical presentation, MRI-PET findings of four groups are assessed.  Groups with presence of flow void showed hypometabolism in the medial frontal and medial temporal lobe. Groups with presence of DESH has effacement of parietal sulci showed parietal hypo metabolism with clinical presentation AD/mixed dementia and absence of parietal effacement showed FTD-like presentation. Groups without flow void or DESH showed only mild medial temporal hypometabolism and presented with classical signs of NPH. ASL perfusion changes are in correlation with metabolism on positron emission tomography (PET)-MRI.  This study has led us to hypothesize the lack of outflow of brain protein and their deposition in parenchyma based on pressure gradient would be easier explanation to go with cluster of findings. MR-PET and other investigations each had different specificity and sensitivity and different pattern of presentation.