Effects of brain ventricular shape on periventricular biomechanics: a finite-element analysis.

Abstract

A computer simulation based on the finite-element method was used to study the biomechanics of acute obstructive hydrocephalus and, in particular, to define why periventricular edema is most prominent in the anterior and posterior horns. Brain parenchyma was modeled as a two-phase material composed of a porous elastic matrix saturated by interstitial fluid. The effects of the cerebrovascular system were not included in this model. The change in the shape of the ventricles as they enlarged was described by two variables, i.e., the stretch of the ependyma and the concavity of the ventricular wall. The distribution of stresses and strains in the tissue was defined by two standard mechanical measures, i.e., the mean effective stress and the void ratio. With obstruction to cerebrospinal fluid flow, the simulation revealed that the degree of ventricular expansion at equilibrium depended on the pressure gradient between the ventricles and the subarachnoid space. Periventricular edema was associated with the appearance of expansive (tensile) stresses in the tissues surrounding the frontal and occipital horns. In contrast, the concave shape in the region of the body of the ventricle created compressive stresses in the parenchyma. Both of these stresses seem to be direct consequences of the concave/convex geometry of the ventricular wall, which serves to selectively focus the forces (perpendicular to the ependyma) produced by the increased intraventricular fluid pressure in the periventricular tissues. The distribution of periventricular edema in acute hydrocephalus is a result not only of increased intraventricular pressure but also of ventricular geometry.