The synergistic effect of acute subdural hematoma combined with diffuse traumatic brain injury on brain edema.

It is well-documented that acute subdural hematoma (ASDH) following diffuse traumatic brain injury (dTBI) contributes to severe disability and high mortality. The objective of this study was to characterize edema formation in a model of ASDH and ASDH following dTBI. Eighteen Sprague-Dawley rats were separated into three groups: Sham operated (n = 6), ASDH (n = 6), ASDH following dTBI (n = 6). Diffuse TBI was produced via the Impact-Acceleration Model [10]. ASDH was induced in the left hemisphere using the well-described method [11]. Total tissue water content was determined 4 hours after TBI utilizing wet-weight/dry-weight assessment. Our results show that ASDH causes a significant increase in tissue water content in the left hemisphere (79.2 +/- 0.7%) compared with the contralateral hemisphere (78.5 +/- 0.5%, p = 0.009). Animals exposed to ASDH following dTBI had significantly greater edema formation than those with ASDH (right: 80.9 +/- 0.4%, left: 80.5 +/- 0.7, p = 0.008). There was no significant difference between the left and right hemisphere. We conclude that edema formation in ASDH is worsened by the combination of dTBI and ASDH. Furthermore a diffuse and focal injury in combination retain the features of the diffuse injury, but with increased severity. Further studies are required to elucidate the synergistic mechanisms involved in these pathological processes.