Effect of Cause of Injury on Lesion Location, Injury Severity and Functional Outcome Following Traumatic Brain Injury
Frank Hillary, M.S., Drexel University University, Psychology Department
Stephen Moelter, M.S., Drexel University, Psychology Department
Philip Schatz, Ph.D., Saint Joseph's University, Psychology Department
Douglas L. Chute, Ph.D., Drexel University University, Psychology Department
Previous research occasioned us to hypothesize that the mechanics of traumatic brain injury produce different anatomical locations and severities of brain injuries. Location of lesion, injury severity, outcome following traumatic brain injury were analyzed for 236 of a pool of 500 individuals who were applicants to the Pennsylvania Head Injury Program. Participants were selected as belonging to one of four major groups based on the circumstances around which they sustained their TBI: motor vehicle occupants wearing seat belts (n=31), unbelted motor vehicle occupants (n=130), victims of assault (n=33), and individuals who suffered TBI from a fall (n=42). Presumably different physical forces exerted at the time of injury for each of these four groups led us to hypothesize that individuals would sustain anatomically different injuries. Belted motor vehicle occupants sustained significantly more subcortical injuries (p<.02), unbelted motor vehicle occupants sustained significantly more posterior cortical lesions (p<.0001), and individuals in the fall and assault groups sustained significantly more epidural and subdural hematomas (p<.0002). Motor vehicle occupants were assigned significantly more impaired Glasgow Coma Scale scores (p<.02) and experienced significantly longer loss of consciousness (p<.05) than individuals in the assault and fall groups. No significant group differences were noted on functional outcome after an average of 3.6 years. These data show that the location and severity of lesion are different as a result of the cause of brain injury. There, however, were no resultant effects on functional outcome.
Traumatic brain injury is most often caused by motor vehicle collisions, falls, sports accidents and violence in the United states (Frankowski, 1986) as well as abroad (Engberg, 1995). Similarly, in Pennsylvania Head Injury Program motor vehicle occupant injury, injury secondary to falls, and victims of assault account for 67% of the head injuries. Considering this, it is important to delineate the effect injury mechanism has on brain injury outcomes.
Evidence in the biomechanical literature has emphasized that inertial and impact forces are distinct physical processes and may be responsible for different forms of brain injury (McIntosh, 1996). In addition , comparison between restrained and unrestrained motor vehicle occupants has revealed differences in brain lesion location (Hillary, Schatz, and Chute, 1997). The purpose of this investigation was to analyze the effects of two additional causes of injury: assault and fall. Thus, location of brain lesion (i.e., the anatomical structures involved), injury severity (measured by Glasgow Coma Scale (GCS), loss of consciousness (LOC) and length of hospitalization) and overall patient outcome at three years following the injury (measured by FIL and DRS scores) were tracked for four groups of brain injury survivors.
Medical charts for 236 survivors of brain injury considered to be domiciled in the state of Pennsylvania at the time of injury who sustained a head injury and applied to the Pennsylvania Head Injury Program (PHIP) between 1985 and 1996. They were selected as belonging to one of four major groups based on the circumstances around which they sustained their TBI: motor vehicle occupants wearing seat belts (n=31), unbelted motor vehicle occupants (n=130), victims of assault (n=33), and individuals who suffered TBI from a fall (n=42).
Participants were included in the study only if their file contained a completed PHIP application, acute care medical records, and evidence of head injury as determined by the PHIP criteria. Approximately 236 individuals were excluded from the study because they did not sustain TBI as a motor vehicle occupant, during a fall, or as a victim of assault. In addition, approximately 22 brain injury survivors were excluded due to negative or equivocal imaging results or incomplete medical/acute care records.
Lesions specified on CT and MRI reports were coded for 27 distinct locations. Cortical lesions were grouped into anterior (frontal lobe) and posterior (parietal/occipital). Subcortical lesions were divided into subcortical (diencephalon and basal ganglia) and brainstem (mesencephalon and metencephalon) groups..
Severity of Injury
Statistical analyses yielded significant differences between groups for injury severity variables. Analysis of Variance revealed a main effect for GCS scores between groups (F (4, 204)= 5.13, p<.002). In addition, a main effect was noted for duration of loss of consciousness between groups (F (4, 196)= 6.38, p<.0005). There were no significant between group differences for length of acute care hospital stay.
Location of Injury
Incidence and location of brain lesion were calculated for both restrained and unrestrained motor vehicle occupants. Statistical analysis was conducted between groups for anterior (frontal lobe) and posterior (occipital and parietal) cortical regions as well as for subdural hematomas, "subcortical" and "brainstem" groupings.
By comparing the average number of lesions sustained in each brain lesion, several significant findings were noted. First, unrestrained motor vehicle occupants (45%) and victims of assault (59%) were significantly more likely to sustain damage in posterior regions of the brain [X2(3) = 13.8, p = 003].
Conversely restrained motor vehicle occupants were significantly more likely to sustain damage in the subcortical regions ((35%) compared to other groups [X2 (3) = 10.2, p = 0.01]. Finally, the incidence of epidural and subdural hematomas was significantly greater in those who fell (52%) and those who were assaulted (69%) when compared to restrained (22%) and unrestrained (32%) motor vehicle occupants [X2 (3) = 20.5, p = 0.0001].
There were no significant between group differences in the incidence of frontal lobe lesions (Falls = 52%, Assaults = 65% ,Restrained = 64% , and Unrestrained =56%). Similarly the frequency of brainstem injury between groups was not significantly different (Falls = 7%, Assaults = 12% ,Restrained = 16% , and Unrestrained =15%)
The fall and assault groups are distinguished from the motor vehicle occupants by having significantly lower levels of education [F (4, 225)= 5.04, p<.002]. The incidence of drugs or ETOH use at the time of injury was significantly higher in the fall (44%) and assault (71%) groups when compared to restrained (4%) and unrestrained (34%) motor vehicle occupants [X2 (3) =26.5, p<0.0001]. In addition, brain injury survivors in the fall and assault groups were more likely to be single [X2 (3) = 12.7, p = 0.04] and male [X2 (3) = 13.4, p = 0.003]. Figure 2 offers a breakdown of marital status.
Analyses revealed no effect of seatbelt use on outcome measures. For FIL scores, the data revealed non-significant differences between restrained occupants (M = 6.125, SD 2.34 ), unrestrained occupants (M = 6.045, SD = 2.32), survivors of a fall (M = 6.40, SD =2.59), and victims of assault (M = 6.41, SD = 2.1). Similarly, for DRS scores, the data revealed non-significant differences between restrained occupants (M = 6.72, SD 4.8 ), unrestrained occupants (M = 7.78, SD = 0.67), survivors of a fall (M = 7.61, SD =6.52), and victims of assault (M = 5.8, SD = 3.76). These findings were noted at an average of 3.6 years post injury.
Cause of injury is appears to play a significant role in lesion location and injury severity following TBI. Functional outcome appears to be less directly affected, however, and there are several plausible explanations for this effect. First, it is likely that the severity of injury in the survivors studied (overall average GCS scores = 5.71) remained significantly impaired after years of recovery. Secondly, socioeconomic and personality variables are believed to contribute to this deleterious effect on functional outcome. The fall and assault groups are distinguished from the motor vehicle occupants by having significantly lower levels of education, significantly higher incidence of alcohol use at the time of injury, and they were less likely to have the social support of a spouse. Thus, we speculate that socioeconomic and personality variables may be contributing to the overall level of functional outcome.
These data show that location of brain injury and injury severity are different as a likely result of the cause of brain injury. Ultimately, by gaining a better understanding of the physical process of brain injury, different methods to protect the central nervous system can be developed.
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