Traumatic brain injury (TBI) is a leading cause of death and disability in the U.S.A. In mild cases, common etiologies of TBI (i.e., hemorrhage or edema) are not readily apparent during medical examination. We propose that the pia-arachnoid complex (PAC) contributes to the brain’s response in TBI. The PAC is the only layer of tissue between the brain and dura (a tough membrane tightly adhered to the skull), and acts as a mechanical tether between the brain and skull. If the fine structures of the PAC are damaged during TBI, they likely go undiagnosed due to their small size and difficulty to image.
To better understand the mechanics of PAC injury, several experimental and computational studies were conducted. First, a novel application of optical coherence tomography (OCT) was utilized to acquire microscale images of the in-situ porcine PAC and measure the amount of arachnoid trabeculae (AT) present. Next, two parametric studies were conducted on a microscale model of the PAC which evaluated its sensitivity to variable substructure moduli and AT volume fraction (VF). Afterwards, the microscale PAC model was paired with a macroscale head model to determine the effect of a nonuniform AT VF on whole-head mechanics. Finally, an immature porcine model of mild TBI was used to investigate PAC damage following head rotation, and identify clinically relevant MRI biomarkers indicative of PAC damage.
The OCT imaging of the PAC revealed high variability of VF within each head, but low variability between brain regions and between animals. The microscale parametric studies showed high sensitivity to changes in substructure moduli and VF. The macroscale model studies showed improvement of intracranial hemorrhage prediction when variable VF was introduced into the models. Clinically relevant biomarkers of PAC damage were not able to be confidently developed, but increased sample size and improved resolution may lead to innovative biomarkers for TBI.
The work presented here addresses a significant lack of data on the PAC, and presents new insights into its anatomy and biomechanics. Many of the studies presented here are the first of their kind, opening up many new paths of TBI research opportunities.
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