Modelling of Diffuse Brain Injury: Combining Methods to Study Possible Links between Transient Intracranial Pressure and Injury

The objectives of this research are the study of sagittal rotational acceleration induced diffuse brain injury mechanisms. Such injuries are common in vehicle accidents in particular; the consequences range from mild to severe symptoms and may lead to persistent neurological dysfunction. The understanding of the mechanisms that lead to these injuries is not yet well established and needs to be studied further. A rabbit animal model was used to study the dynamic brain pressure response and the injury outcome. Rabbits were subjected to sagittal rotational acceleration of the head, during which the intracranial pressure changes were recorded by fibre optic pressure sensors inserted into the brain parenchyma at selected locations. Both flexion and extension were investigated for two levels of acceleration. A neuropathological investigation was carried out. In parallel, a rabbit brain FE model was developed to further understand the biomechanics of the experiments and experimental design. The direction of the acceleration applied was found to influence the intracranial pressure measurements, as disclosed by the prominent negative pressure patterns as a result of flexion of the head, which diverged from those recorded in extension. In the extension experiments an initial pressure rise followed by a pressure drop was observed. Such divergence in brain response was also found for the injury outcome. For similar low levels of acceleration, a flexion trauma induced prominent histopathological changes in the brain while an extension trauma induced minimal abnormalities. Evidence for the relative motion between the brain and skull was found for flexion loading. In these subjects, scattered ruptured bridging veins were observed and stretching of the olfactory bulbs and nerves. Such injuries were not observed in extension. The FE model was suitable for predicting pressure in extension load cases. The FE could help to refine the experimental design by suggesting new measurement locations in the brain, which are less sensitive to the measured pressure variations. This study shows that the combination of the three methods, the measurement of an internal parameter (pressure) in the brain, neuropathological investigation of the injury outcome, and finite element simulations of the experiments, could help to promote more detailed knowledge of brain injury mechanisms. Such knowledge could be used to develop countermeasures and, thereby to reduce the number and severity of brain injuries in traffic related accidents