Severity level and injury track determine outcome following a penetrating ballistic-like brain injury in the rat

Penetrating ballistic brain injury (PBBI) is a high-energy transfer wound causing direct damage to the cerebrum. Outcome is directly related to the ballistic's anatomical path and degree of energy transfer. In this study we evaluated differences in outcome induced by altering the 'projectile' paths and severity levels of a simulated bullet wound using a newly characterized rat model of PBBI. Severity levels (5, 10, and 15%) were compared across three distinct injury paths: (1) unilateral 'frontal', (2) 'bilateral' hemispheric, and (3) unilateral 'caudal' (including cerebellum/midbrain). Outcome was assessed by differences in mortality rate and motor dysfunction (e.g. neurological and balance beam deficits). Results indicated that outcome was dependent not only on the severity level of PBBI (P < 0.001, r = 0.535) but also brain regions injured (P < 0.001, r = 0.398). A unilateral caudal injury was associated with the highest degree of mortality (up to 100%) and motor dysfunction (64-100% disability). Bilateral hemispheric injuries were also potentially fatal, while the best outcomes were associated with a unilateral frontal injury (no mortality and 14-39% motor disability). These data closely resemble clinical reports of ballistic wounds to the head and further validate the rat PBBI model with the ultimate intent to investigate novel therapeutic approaches for diagnosis and treatment of the neuropathological damage associated with PBBI.