The mechanism underlying the occurrence of traumatic brainstem lesions in victims of traffic accidents.

Autopsy records and photographs of traffic accident deaths from 1985 to 2000 as well as police reports were reviewed to determine the morbidity and pathological features of traumatic brainstem lesions and to determine the relationship between lesions and forces applied. Of 156 autopsied traffic accident cases, 26 (16.7%) of the victims had gross primary brainstem injury. The 26 victims included 19 pedestrians, five cyclists, one driver and one passenger. There were four cases of upper face impact and two cases of lower face impact in which the direct forces to the head had caused hyperextension of the neck. However, eight of the pedestrians and two of the cyclists had medullary lesions for which the cause could not be explained by the direct impact to the head, suggesting that indirect forces, i.e. the inertia of the head, had caused neck hyperextension at the moment of impact with the car. Based on the findings in this study, it was concluded that when a pedestrian or cyclist is hit by a vehicle travelling at high speed, the traction force due to the inertia of the head is one of the causes of violent hyperextension of the head that result in traumatic brainstem lesions.