Head injuries are generally divided into two types: closed and open or penetrating (Graham et al., 2002). In open or penetrating injuries, the skull is breached, most commonly struck with violent force by foreign objects during an assault or from a gun shot or as a result of the head impacting some part of the vehicle in a motor vehicle accident (MVA). Part of the damage from penetrating injuries often includes bone fragments and other debris associated with the trauma that directly injures the brain. In addition to the mechanical damage to brain tissue, there is typically local haemorrhaging that also damages the brain, since the forces that penetrate the brain usually tear blood vessels in the region of penetration. The pathological consequences of open or penetrating injuries to the brain are most likely to produce focal brain injuries, although often generalized damage may also occur. Open head injuries are less common than closed and some, like gunshot wounds (GSW) to the head, are associated with very high mortality.

The most common head injury associated with survival is a closed head injury (CHI), where the brain is injured by the mechanical, concussive and movement forces within the cranium, secondarily through impact to the head and/or acceleration/deceleration forces. Either regional or global, such forces place what are referred to as tensile or shear-strain effects throughout the brain. These effects have the potential to stretch neural tissue, particularly axons, which in turn damages either their structure or function.