The Stereotactical Phenomena in Traumatic Brain Injury Biomechanics: Diffuse Axonal Injury and Concussion

Dr. C. OBREJA
NTCP@ - not-for-profit organization
211, rue Robespierre, 93170 Bagnolet, France
Email: ntcp@neurostaff.org
Web site: www.neurostaff.org

THE STEREOTACTICAL THEORY

The stereotactical approach considers the geometrical shape of the interface skull-brain, the close interactions between the two structures during their relative movements and the resultant pressure waves propagation.

The shape of the interface skull-brain is approximately spherical. The skull-brain relative movements, caused by the acceleration phenomena - linear or rotational - and by the skull vibrations, generate secondary pressure waves with an approximately spherical wave front. Because the brain tissue is isotrop on concentric plans, the wave propagation velocity toward the deep cerebral structures is spatially homogenous.

C = (E/r)0,5
C = wave propagation velocity; E = resilience; r = density

The spherical shape of the wave front is thus conserved. Its spoke and its surface progressively decrease. Despite attenuation phenomenon and according to the energy conservation law, the amplitude of the pressure waves, and thus the pressure gradient, progressively increases toward the deep cerebral structures. It will be maximal in the geometrical centre of the implied skull vault segment (figure 1), particularly if no significant energy consumption process occurs in the superficial cerebral structures before. If such a superficial cerebral contusion occur, a pressure wave "shadow cone" is delimited towards the deep cerebral structures and thus the stereotactical summation phenomena are partly perturbed.

Figure 1: The stereotactical concept illustrated on a sagital MRI view

In low or medium-energy impacts, the skull vibrations have a significant role by generating successive wave fronts. Cumulative effects related to the temporal summation phenomena thus add to the spatial (stereotactical) ones.

In high-energy impacts, the acceleration phenomena are predominant. Because of the skull fractures that often occur, the skull vibrations are perturbed and their stereotactical consequences reduced. In the mean time, the high acceleration effects diminish the relative importance of the skull vibrations' consequences.

CONTENTS
Introduction
Current Biomechanical Theories
Discussion and Conclusion
References