Pong Alice C, Jugé Lauriane, Bilston Lynne E, Cheng Shaokoon
Neuroscience Research Australia, Margarete Ainsworth Building, Barker Street, Randwick, Sydney, NSW, Australia.
University of New South Wales, School of Medical Sciences, Wallace Wurth Building, Kensington, Sydney, NSW Australia.
PLoS One. 2017 Aug 24;12(8):e0182808. doi: 10.1371/journal.pone.0182808. eCollection 2017.
Regional changes in brain stiffness were previously demonstrated in an experimental obstructive hydrocephalus juvenile rat model. The open cranial sutures in the juvenile rats have influenced brain compression and mechanical properties during hydrocephalus development and the extent by which closed cranial sutures in adult hydrocephalic rat models affect brain stiffness in-vivo remains unclear. The aims of this study were to determine changes in brain tissue mechanical properties and brain structure size during hydrocephalus development in adult rat with fixed cranial volume and how these changes were related to brain tissue deformation.
Hydrocephalus was induced in 9 female ten weeks old Sprague-Dawley rats by injecting 60 μL of a kaolin suspension (25%) into the cisterna magna under anaesthesia. 6 sham-injected age-matched female SD rats were used as controls. MR imaging (9.4T, Bruker) was performed 1 day before and then at 3 days post injection. T2-weighted anatomical MR images were collected to quantify ventricle and brain tissue cross-sectional areas. MR elastography (800 Hz) was used to measure the brain stiffness (G*, shear modulus).
Brain tissue in the adult hydrocephalic rats was more compressed than the juvenile hydrocephalic rats because the skulls of the adult hydrocephalic rats were unable to expand like the juvenile rats. In the adult hydrocephalic rats, the cortical gray matter thickness and the caudate-putamen cross-sectional area decreased (Spearman, P < 0.001 for both) but there were no significant changes in cranial cross-sectional area (Spearman, P = 0.35), cortical gray matter stiffness (Spearman, P = 0.24) and caudate-putamen (Spearman, P = 0.11) stiffness. No significant changes in the size of brain structures were observed in the controls.
This study showed that although brain tissue in the adult hydrocephalic rats was severely compressed, their brain tissue stiffness did not change significantly. These results are in contrast with our previous findings in juvenile hydrocephalic rats which had significantly less brain compression (as the brain circumference was able to stretch with the cranium due to the open skull sutures) and had a significant increase in caudate putamen stiffness. These results suggest that change in brain mechanical properties in hydrocephalus is complex and is not solely dependent on brain tissue deformation. Further studies on the interactions between brain tissue stiffness, deformation, tissue oedema and neural damage are necessary before MRE can be used as a tool to track changes in brain biomechanics in hydrocephalus.
先前在实验性梗阻性脑积水幼年大鼠模型中已证实脑硬度存在区域变化。幼年大鼠开放的颅骨缝在脑积水发展过程中影响了脑压缩和力学性能，而成年脑积水大鼠模型中闭合的颅骨缝在体内对脑硬度的影响程度仍不清楚。本研究的目的是确定固定颅腔容积的成年大鼠在脑积水发展过程中脑组织力学性能和脑结构大小的变化，以及这些变化与脑组织变形之间的关系。
对9只10周龄雌性斯普拉格-道利大鼠在麻醉下经枕大池注射60μL高岭土悬浮液（25%）诱导脑积水。6只年龄匹配的假注射雌性SD大鼠作为对照。在注射前1天和注射后3天进行磁共振成像（9.4T，布鲁克）。采集T2加权解剖磁共振图像以量化脑室和脑组织横截面积。磁共振弹性成像（800Hz）用于测量脑硬度（G*，剪切模量）。
成年脑积水大鼠的脑组织比幼年脑积水大鼠受到更严重的压缩，因为成年脑积水大鼠的颅骨不能像幼年大鼠那样扩张。在成年脑积水大鼠中，皮质灰质厚度和尾状核-壳核横截面积减小（两者的斯皮尔曼相关系数，P均<0.001），但颅横截面积（斯皮尔曼相关系数，P = 0.35）、皮质灰质硬度（斯皮尔曼相关系数，P = 0.24）和尾状核-壳核硬度（斯皮尔曼相关系数，P = 0.11）无显著变化。对照组脑结构大小无显著变化。
本研究表明，尽管成年脑积水大鼠的脑组织受到严重压缩，但其脑组织硬度没有显著变化。这些结果与我们先前在幼年脑积水大鼠中的发现相反，幼年脑积水大鼠的脑压缩明显较小（由于开放的颅骨缝，脑周长能够随颅骨伸展），且尾状核-壳核硬度显著增加。这些结果表明，脑积水时脑力学性能的变化很复杂，并不完全取决于脑组织变形。在磁共振弹性成像能够用作追踪脑积水时脑生物力学变化的工具之前，有必要进一步研究脑组织硬度、变形、组织水肿和神经损伤之间的相互作用。
