Traumatic brain injury: The first 15 milliseconds

Abstract

Objective: The physical events of the first 15 milliseconds of a traumatic brain injury are reviewed from computer simulations using finite element calculations and applied to observed pathology.

Methods: The impact creates two shock waves; one through the brain, another through the skull, both injure the brain separately. Two accelerations, anteroposterior and rotary, distort or stretch the brain, because of inertia. The two shockwaves are reflected many times within in the brain, from boundaries where the density or elasticity changes.

Results: Overlapping waves form powerful positive or negative pressure nodes. Negative waves are more damaging to neurones and blood vessels, so a random pattern of scattered neural and capillary necroses develop all over the brain. The skull shockwave expands the skull opposite the blow, so creating a damaging negative pressure injury to the brain, contre coup contusion. Acceleration (or deceleration) follows impact, beginning later and lasting longer. Inertia strains the tissue, where the brain is free to move, inflicting characteristic white matter injuries.

Conclusions: In the antero-posterior plane, acceleration and inertia stretch and tear long tracts to the spine and blood vessels running from the brain to the dura. Rotatory accelerations stress the inter-hemispheric connections of the brain, especially the corpus callosum, between the hemispheres.

Keywords:

• TBI (traumatic brain injury)
• shock waves
• physics
• physical properties of brain
• brain concussion

Acknowledgements

This has been done by private study, but the author is grateful to have used the library facilities of the Accident Compensation Corporation of New Zealand. No funding has been received for it and no competing positions are held. I am very grateful to Professor Robert Vink of University of South Australia, who offered advice while the paper was in preparation. The opinions expressed are the personal views of the author, in retirement from active neurosurgical practice, not those of his employer, the Accident Compensation Corporation of New Zealand.

Declaration of interest

The author reports no conflicts of interest. The author alone is responsible for the content and writing of the paper.

Notes

¹ The expansion of 4^th ventricle, from the aqueduct, lets a ventricular shock wave transmit more energy to the cerebellum than to the lesser area of the walls of the aqueduct. If the area of the ventricular wall increases, the energy deposited by a shock wave increases; the expanded shape increases the surface area on which the pressure pulse pushes, so increasing the energy transferred. (Like a hydraulic jack; or press, a small force on a small piston is multiplied many times in the force exerted on the larger piston of the jack, or press.)

² These are the most anterior parts of the cerebellum. The term ‘anterior cerebellum’ is in fact the superior part, the nomenclature is evolutionary, based on quadruped anatomy.