The significance of pontomedullar laceration in car occupants following frontal collisions: A retrospective autopsy study.

The aim of this study was to determine the frequency of brainstem pontomedullar lacerations among fatally injured car occupants in head-on collisions, as well as the concomitant cranial injuries, and to establish a possible underlying mechanism for brainstem laceration. Brainstem pontomedullar lacerations (PML) are often associated with fractures of the skull base (hinge, ring or pyramidal fractures) or with cervical spine fractures. Out of 705 cases of deceased car occupants involved in head-on car collisions, some form of head injury was present in 447 cases (63.4%). These cases included 353 men and 94 women with an average age of 38.2±15.8 years (range 16-89 years). The collected cases included 229 drivers, 164 front-seat and 54 rear-seat passengers. PML were present in 67 of these cases (15%), 50 men and 17 women with an average age of 42.9±15.6 years (range 15-77 years), including 32 drivers, 26 front-seat and 9 rear-seat passengers. In all of these cases the brainstem laceration was partial and the depth varied approximately from 4mm to 8mm. To understand the mechanisms by which PML occurs, we classified the head impact areas into frontal, lateral, posterior and chin area, depending on the injuries to the soft tissue of the head and scalp, as well as facial and cranial fractures. Injury impact area of the head was a good predictor of PML occurrence (χ(2)=131.112, df=3, p=0.000). Chin impact was most often associated with PML-38 cases (Wald. coeff.=5.805, df=1, p=0.016). Presence or absence of mandibular fracture was significant for PML occurrence (χ(2)=11.413, df=1, p=0.001): persons without mandibular fracture have 2.3 times greater risk for PML than those with fracture (odd ratio=7.196). Among the observed skull base fractures, the best predictor of PML was ring fracture (Wald. coeff.=30.729, df=2, p=0.000). Our study showed that PML was present in a significant number of car occupants sustaining head injuries in head-on collisions (15%). Impact to the chin with or without a ring fracture to the skull base most often led to this fatal injury, probably after collision with the dashboard.