LATERAL CORTICAL IMPACT INJURY IN RATS - PATHOLOGICAL EFFECTS OF VARYING CORTICAL COMPRESSION AND IMPACT VELOCITY

Direct lateral cortical impact through the intact leptomeninges using a pneumatically driven piston produces increasingly severe pathophysio logic derangements with increasing cortical deformation. We studied th e histopathologic correlates of cortical impact injury produced by 2 m m, 2.5 mm, and 3 mm deformation in the rat at 5 m/sec. Additionally, t he effect of impact velocity at a 2.5 mm deformation was assessed at 1 m/sec, 3 m/sec, and 5 m/sec. The brains were examined 14 days after i njury. Cortical contusion maximum cross-sectional area, volume, and th e percentage CA1 and CA3 hippocampal neuronal loss correlate with cort ical deformation and impactor velocity. Contusion volume increased wit h increasing cortical deformation. Deformations of 2, 2.5, and 3 mm at 5 m/sec produced contusion volumes of 4.59, 8.9, and 21.68 mm(3), res pectively. At a fixed cortical deformation of 2.5 mm, contusion volume increased with increasing impact velocity. Impact velocities of 1, 3, and 5 m/sec produced contusion volumes of 5.79, 7.42, and 8.9 mm(3), respectively. Hippocampal CA3 neuronal loss increased with increasing cortical deformation. Deformations of 2, 2.5, and 3 mm at 5 m/sec prod uced neuronal loss of 29%, 48.3%, and 79.5%, respectively. At a fixed cortical deformation of 2.5 mm, hippocampal CA3 neuronal loss increase d with increasing impact velocity. Impact velocities of 1, 3, and 5 m/ sec produced neuronal loss of 18.25%, 33.75%, and 48.3%, respectively. Hippocampal CA1 neuronal loss was also seen and paralleled cortical d eformation and impact velocity. Cortical deformation and impact veloci ty are critical parameters in producing cortical contusion and must be considered when comparing results using this model.