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

INTRODUCTION

Traumatic brain injury (TBI) is the main cause of death for patients less than 45 (1). TBI biomechanics explores the mechanical phenomena that cause the initial cranio-cerebral lesions and thus represents the starting point for the overall understanding of the TBI pathophysiology. TBI is the consequence of the spatiotemporal pressure variations occuring inside the brain during head traumas. The spatial distribution of the pressure gradient (PG) is responsible for the tissue strains (compression, tensile, shear), the cerebral lesions' localisation and the consequent neurological signs (2). Beside skull's deformation caused by the contact loading and determining skull vibrations and/or fractures, current biomechanical theories concern two inertial phenomena: the linear acceleration and the rotational head movements. The first theory explains the superficial brain lesions. The second theory seems better explain the deep cerebral lesions and the concussion mechanism but is still controversed (3). Here is exposed a new biomechanical approach that can explain the deep cerebral lesions and the common neurological signs observed after human head traumas.

Traumatic brain lesions
Focal and diffuse cerebral lesions are currently described. The focal lesions, also called cerebral contusions, are haemorrhagical and are visible on frequently performed radiological exams as the X-ray computed tomography. The focal lesions are often located in the superficial brain structures, close from the skull, but sometimes deep cerebral hematomas occur. The focal lesions always coexist with different degrees of diffuse cerebral lesions, also called "diffuse axonal injury" (DAI). The DAI is concentrated in the deep cerebral regions and is not visible on the radiological exams. Meanwhile, in accordance with its severity, the DAI is mainly responsible of various degrees of consciousness disturbances and further clinical outcome (2). The clinical entity corresponding to the rather pathological sense of the DAI term is the brain concussion.

CONTENTS
Current Biomechanical Theories
The Stereotactical Theory
Discussion and Conclusion
References