Pontomedullary tears and other gross brainstem injuries after vehicular accidents.

In a series of 988 autopsied victims of road crashes, there were 36 (3.6%) cases of gross primary brainstem injury. These fell into three groups. The first comprised eight cases of pontomedullary tearing without other gross brain injury: in seven of these, there were associated atlanto-occipital dislocations and/or high cervical fracture-dislocations. The usual cause appeared to be facial impact inducing acute hyperextension. Second, there were 17 cases of pontomedullary tearing associated with other brainstem lacerations and/or major damage elsewhere in the brain: in all, there were fractures of the skull base, typically transverse middle fossa fractures. Most of these injuries appeared to be due to facial impacts transmitting force to the anterior skull base, although hyperextension was also a factor in some. There was a third heterogeneous group of 11 cases with brainstem lacerations in sites other than the pontomedullary junction: in some of these it appeared that the impacts had caused skull base fractures by inducing calvarial torsion. In this series, the proportion of motorcyclists (41.7%) was double the expected figure. The use of a helmet modifies the mechanisms of impact head injury; the overall benefits of helmet use are well established, but there is need for more research on helmet design.