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

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.