The Tight Medial and High Convexity Subarachnoid Spaces Is the First Finding of Idiopathic Normal Pressure Hydrocephalus at the Preclinical Stage

Abstract

Disproportionately enlarged subarachnoid-space hydrocephalus (DESH) findings are often reported as characteristic radiological features of idiopathic normal pressure hydrocephalus (iNPH). However, the process of development of DESH remains unclear. The aim of the present study was to determine the dynamic deforming process and pathophysiology of iNPH. All patients >50 years of age who underwent whole body FDG-PET/CT scanning at Kindai University Hospital between May 2017 and April 2018 were included in this retrospective study, and their brain image findings and clinical information were assessed. We defined DESH-like findings, which had one or two equivocal features of the three components of DESH findings, as preclinical morphologic features of DESH (PMD). PMD were classified into six subtypes based on their component of DESH findings: PMD-T, only tight medial and high convexity subarachnoid spaces (TMC); PMD-S, only enlarged Sylvian fissures; PMD-V, only ventriculomegaly; PMD-TV, TMC and ventriculomegaly; PMD-TS, TMC and enlarged Sylvian fissures; PMD-SV, enlarged Sylvian fissures and ventriculomegaly. A total of 2196 cases (70.5 ± 9.3 years) were enrolled, with 54 cases (77.1 ± 5.9 years) with DESH findings, and 42 cases (72.9 ± 7.9 years) with PMD (five PMD-T, two PMD-V, 12 PMD-TV, 18 PMD-TS, and five PMD-SV). In each component of DESH, 35 of 42 (83.3%) cases with PMD had TMC. We suggest that the TMC is the first change on DESH findings in most iNPH cases, and may be an important part of the pathophysiology of iNPH.

Changes in cerebral glucose metabolism caused by morphologic features of prodromal idiopathic normal pressure hydrocephalus

“…To our knowledge, this is the first report assessing the changes in regional cerebral glucose metabolism using FDG-PET/CT in the prodromal stage of iNPH. We previously reported that iNPH develops in the order of PMD, AVIM, and iNPH [13], with PMD (asymptomatic incomplete DESH) progressing to AVIM (asymptomatic complete DESH), which processes to iNPH (symptomatic complete DESH). In this study, we also evaluated cerebral glucose metabolism during the progression of iNPH.…”

“…We retrospectively reviewed the medical records for brain images and clinical features of all 2196 patients, who are > 50 years of age and who underwent a whole body FDG-PET/CT scanning at Kindai University Hospital between May 1, 2017 and April 31, 2018 [13]. There were 79 cases with preclinical or clinical iNPH from this cohort (based on brain morphologic features of iNPH), and they were enrolled in the present study.…”

“…PMD was defined as an asymptomatic subject with incomplete DESH-like findings, AVIM defined as an asymptomatic subject with complete DESH findings and iNPH as a symptomatic subject with complete DESH findings. We considered that iNPH develops in the order of PMD, AVIM, and iNPH, as reported [13]. We previously hypothesized that the progression of iNPH could be determined by PMD characteristics (i.e., younger age than AVIM and iNPH, incomplete DESH-like findings, and asymptomatic).…”

“…The kappa coefficient of this classification was 0.823. A detailed description of this classification was previously reported [13].…”

“…Recently, we performed a cross-sectional study on >2000 elderly people who underwent a whole body FDG-PET/CT scanning and reported prevalence and morphology of cases with both preclinical and clinical iNPH [13]. In the present study, we evaluated and compared the regional cerebral FDG uptake between preclinical and clinical iNPH patients from that study with normal controls (NC) matched for each group, to elucidate the progression of changes in cerebral glucose metabolism, particularly in the preclinical stage of iNPH, and further understand the pathological mechanisms of iNPH.…”