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

OBJECTIVE: A computer simulation based on the finite-element method was use d to study the biomechanics of acute obstructive hydrocephalus and, in part icular, to define why periventricular edema is most prominent in the anteri or and posterior horns. METHODS: 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 mot included in this model. The change in the s hape 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. T he distribution of stresses and strains in the tissue was defined by two st andard mechanical measures, i.e., the mean effective stress and the void ra tio. RESULTS: With obstruction to cerebrospinal fluid flour, the simulation reve aled that the degree of ventricular expansion at equilibrium depended on th e pressure gradient between the ventricles and the subarachnoid space. Peri ventricular edema was associated with the appearance of expansive (tensile) stresses in the tissues surrounding the frontal and occipital horns. In co ntrast, the concave shape in the region of the body of the ventricle create d 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 ependy ma) produced by the increased intraventricular fluid pressure in the perive ntricular tissues. CONCLUSION: The distribution of periventricular edema in acute hydrocephalu s is a result not only of increased intraventricular pressure but also of v entricular geometry.