Pontomedullary lacerations in pedestrians: an autopsy study.

It is common that injuries to the head are among the most frequent injuries found in pedestrian accidents, and can constitute a serious, if not fatal, threat. Brainstem lesions have only occasionally been reported in pedestrian injuries. The aim of this study has been to determine the frequency of brainstem pontomedullary lacerations (PMLs) among fatally injured pedestrians, the frequency of concomitant cranial, facial and cervical spine injuries in such cases, as well as to establish their possible underlying mechanism. In this work, PML was present in a significant number of fatally injured pedestrians from a sample of 50 out of 360 cases with head injuries (14%). When observed alone, the most frequent head impact areas were the chin, lateral and frontal (χ(2) = 14.200, df = 4, P = 0.007) in the subgroup with PML. Hinge fractures were most often seen in this subgroup (25 cases), followed by the absence of skull base fractures (χ(2) = 26.320, df = 3, P < 0.01). There are several possible mechanisms of PML in these cases. Impact to the chin, with or without a skull base fracture, could lead to this fatal injury due to impact force transmission. Additionally, lateral head impacts, the most frequent in pedestrians, with subsequent hinge fractures, PML and fronto-posterior hyperextension of the head that is associated with upper-spine fractures, may be possible mechanisms of brainstem injury in fatally injured pedestrians.