From the Department of Neurosurgery (S.Y., K.N.), Shiga University of Medical Science, Shiga, Japan
Department of Neurosurgery and Normal Pressure Hydrocephalus Center (S.Y., K.Y., M.Y.), Rakuwakai Otowa Hospital, Kyoto, Japan.
AJNR Am J Neuroradiol. 2021 Mar;42(3):479-486. doi: 10.3174/ajnr.A6941. Epub 2021 Jan 21.
Oscillatory shear stress could not be directly measured in consideration of direction, although cerebrospinal fluid has repetitive movements synchronized with heartbeat. Our aim was to evaluate the important of oscillatory shear stress in the cerebral aqueduct and foramen magnum in idiopathic normal pressure hydrocephalus by comparing it with wall shear stress and the oscillatory shear index in patients with idiopathic normal pressure hydrocephalus.
By means of the 4D flow application, oscillatory shear stress, wall shear stress, and the oscillatory shear index were measured in 41 patients with idiopathic normal pressure hydrocephalus, 23 with co-occurrence of idiopathic normal pressure hydrocephalus and Alzheimer-type dementia, and 9 age-matched controls. These shear stress parameters at the cerebral aqueduct were compared with apertures and stroke volumes at the foramen of Magendie and cerebral aqueduct.
Two wall shear stress magnitude peaks during a heartbeat were changed to periodic oscillation by converting oscillatory shear stress. The mean oscillatory shear stress amplitude and time-averaged wall shear stress values at the dorsal and ventral regions of the cerebral aqueduct in the idiopathic normal pressure hydrocephalus groups were significantly higher than those in controls. Furthermore, those at the ventral region of the cerebral aqueduct in the idiopathic normal pressure hydrocephalus group were also significantly higher than those in the co-occurrence of idiopathic normal pressure hydrocephalus with Alzheimer-type dementia group. The oscillatory shear stress amplitude at the dorsal region of the cerebral aqueduct was significantly associated with foramen of Magendie diameters, whereas it was strongly associated with the stroke volume at the upper end of the cerebral aqueduct rather than that at the foramen of Magendie.
Oscillatory shear stress, which reflects wall shear stress vector changes better than the conventional wall shear stress magnitude and the oscillatory shear index, can be directly measured on 4D flow MR imaging. Oscillatory shear stress at the cerebral aqueduct was considerably higher in patients with idiopathic normal pressure hydrocephalus.
由于脑脊液的重复运动与心跳同步，具有方向性，因此不能直接测量振荡剪切应力。我们的目的是通过比较特发性正常压力脑积水患者的脑导水管和枕骨大孔的振荡剪切应力与壁面剪切应力和振荡剪切指数，来评估其在脑导水管和枕骨大孔中的重要性。
通过 4D 流应用，测量了 41 例特发性正常压力脑积水患者、23 例特发性正常压力脑积水合并阿尔茨海默病痴呆患者和 9 名年龄匹配的对照组患者的振荡剪切应力、壁面剪切应力和振荡剪切指数。比较了这些脑导水管的剪切应力参数与枕骨大孔和脑导水管的孔径和脑血流量。
通过转换振荡剪切应力，将心跳过程中的两个壁面剪切应力幅度峰值变为周期性振荡。特发性正常压力脑积水组脑导水管背侧和腹侧的平均振荡剪切应力幅度和时均壁面剪切应力值明显高于对照组。此外，特发性正常压力脑积水组脑导水管腹侧的也明显高于特发性正常压力脑积水合并阿尔茨海默病痴呆组。脑导水管背侧的振荡剪切应力幅度与枕骨大孔直径显著相关，而与脑导水管上端的脑血流量呈强相关，而与枕骨大孔的脑血流量无关。
振荡剪切应力比传统的壁面剪切应力幅度和振荡剪切指数更能反映壁面剪切应力矢量的变化，可直接在 4D 流 MR 成像上测量。特发性正常压力脑积水患者脑导水管的振荡剪切应力明显较高。
