Injuries to the head can be grouped into two broad categories based on the mechanism by which the injury is produced: Impact injuries and acceleration or deceleration injuries.
Impact injuries are caused when an object strikes or is struck by the head. These injuries consist of the local effects of contact between the head and the object. Typically, these injuries are:
• Soft tissue injuries: lacerations, abrasions, and contusions of the scalp
• Fracture of the skull
• Contusions of the brain
• Epidural hematomas
• Intracerebral hemorrhages
Acceleration or deceleration injuries are due to sudden movement of the head the instant after injury, with resultant production of intracranial pressure gradients and the subjecting of the brain to both shearing and tensile forces. Two types of injuries are typically produced: (1) Subdural hematomas and (2) diffuse axonal injury.
Subdural hematomas are secondary to tearing of the subdural bridging veins; diffuse axonal injury is secondary to injury to the axons.1 While acceleration or deceleration injuries are associated with impact, theoretically, impact is not necessary for the production of these injuries, just sudden angular rotation of the head. In situations encountered by forensic pathologists, however, acceleration or deceleration injuries of the brain involve impact.
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