Forensic medical analysis of closed head acceleration-deceleration injuries: a narrative review

A key classification of closed head injuries, particularly relevant for reconstructing trauma biomechanics and of greatest medicolegal importance, is the distinction between contact injuries and acceleration-deceleration injuries. The two most characteristic acceleration-deceleration injuries are acute subdural hematoma (ASDH) and diffuse axonal injury (DAI), which both arise from acceleration forces applied to the head but differ in the duration of these forces. ASDH typically results from rapid deceleration against a firm surface, as occurs in falls, falls accompanied by blows, or traffic accidents in which the head strikes the ground directly, with cyclists and motorcyclists being particularly vulnerable. In contrast, DAI is associated with prolonged acceleration-deceleration forces, usually of lower magnitude, and occurs most frequently in vehicular traffic accidents, where deformable or padded surfaces extend the deceleration phase. DAI may also result from falls from considerable heights. This review discusses the development of knowledge regarding DAI, its definition, diagnostic criteria, and key considerations, based on a literature review. Post-mortem detection requires a comprehensive forensic-neuropathological examination of fixed brain tissue, with immunohistochemistry using antibodies against β-amyloid precursor protein (β-APP) remaining the method of choice to visualize damaged axons and distinguish traumatic from ischemic patterns of injury. In conclusion, although ASDH and DAI are both acceleration injuries and may occasionally co-occur, current evidence suggests that their coexistence more likely reflects complex injury mechanisms rather than a single, shared pathway.