Finite element analysis of an elastic model of the brain: distortion due to acute epidural hematoma--the role of the intra-ventricular pressure gradient.

INTRODUCTION: Recent studies on biomechanical properties of brain tissue have focused on computer simulation of this tissue during impacts, simulation of neurosurgical procedures, and improvements in navigational systems for image guided surgery. Several models have been proposed to explain the mechanical behavior of brain tissue in different conditions (dynamic, static and quasi-static), but the role of the ventricles and intra-ventricular pressure has not been studied so much, especially under static loading. It is clear that the ability of biomechanical models to predict the displacement of midline structures secondary to epidural hematoma could effectively improve the accuracy of intra-operative navigational systems. In addition, simulation of midline shift can help us to understand the mechanisms involved in pathogenesis of these conditions. Plain strain computer modeling based on finite element methods has been used to study the degree of displacement and deformation of the ventricles in acute epidural hematoma to determine the more important factors in achieving a more accurate model.

MATERIALS AND METHODS: A patient with an acute epidural hematoma was used to produce a plain strain elastic model of brain tissue. The model was based on the CT data. The displacement of reference points in the modeled ventricle with changing intra-ventricular pressure gradients was compared with the displacement of similar points in the real ventricle as calculated from the CT scan, and the pressure gradients that resulted in the minimum error were determined.

RESULTS: Our data showed that best results were achieved when the pressure gradient was 1.25 KPa (9.4 mm Hg). Also, the ventricle ipsilateral to the hematoma was predicted to be compressed from both the medial and lateral walls.

CONCLUSION: In the plain strain biomechanical modeling of the brain in unilateral strain loading (conditions similar to those used in image guided systems), the intra-ventricular pressure gradients should be considered in order to achieve accurate results. In addition, the so-called "strain shadow effect" is emphasized.