Biomechanical characteristics of brain edema: the difference between vasogenic-type and cytotoxic-type edema

Some of the basic biomechanical properties of edematous brain tissue have yet to be clarified. Therefore we measured regional tissue compliance and swelling isotropy/anisotropy in cat brain during development of vasogenic-type and cytotoxic-type edema. In vasogenic-type edema induced by cryogenic injury, the edematous white matter showed an increase of regional tissue compliance (indentation method), which paralleled the increase in the regional tissue water content (gravimetry). Swelling of the white matter due to edema was anisotropic, in which expansion transverse to the neuronal fibers caused by their dissociation was 91.1%, whereas longitudinal expansion was 2.3%. In cytotoxic-type edema induced by cerebral ischemia for 3 h, regional tissue compliance was decreased in the area suffering energy failure, which was visualized as an area of reduced succinic dehydrogenase activity. The ischemic gray matter showed isotropic swelling, and morphologically, prominent swelling of neuroglial cells. These marked differences in basic biomechanical properties between vasogenic-type and cytotoxic-type edema should be taken into account when analyzing the mechanism of edema-mediated tissue injury.