Of 89 occupants in the CIREN database with SDH, 57 had adequate soft tissue CT data collected within 24
h post-crash demonstrating the injury. The independent variables listed in the Statistical analysis
section were collected for each occupant. A summary of the data is located in . The greatest delta-v/BES and maximum crush was observed for occupants in frontal crashes. The greatest percent SDH, SDH volume and midline shift was seen in the single occupant involved in a rollover crash. However, of the most frequent crash modes (frontal, near-side, and far-side), the greatest percent SDH and SDH volume was observed in far-side crashes, as seen in and . In , the percent SDH is plotted versus the principal direction of force (PDOF). The PDOF is the angle between the vehicle's longitudinal axis and impulse vector resulting from the impact. Values in this plot have been symmetrically adjusted with respect to the occupant to represent the near-side or far-side value from the perspective of a United States driver. The majority of occupants in all crash modes were belted; however, a large number of occupants in frontal crashes were unbelted.
Summary of the Crash, Occupant, and Injury Data Collected for the 57 SDH Occupants
FIG. 2. Polar plot of % subdural hematoma (SDH) by principal direction of force (PDOF) with the radial measurement as the % SDH. The resulting near-side and far-side PDOF marker is relative to the seating location of the occupant within the vehicle and the location (more ...)
The occupants ranged in age from<1 year old to 86 years old. Thirty-two occupants were female and 25 were male. Of the 57 occupants, 5 died and 52 did not. Three out of the five fatalities were in frontal crashes. In addition to sustaining a SDH, a variety of additional intracranial injuries were present, including subarachnoid hemorrhage (40%), unilateral intraparenchymal contusion (12%), intraventricular hemorrhage (12%), pneumocephalus (11%), multiple intraparenchymal contusions (7%), and epidural hematoma (5%). One occupant also sustained a diffuse axonal injury. The SDH was located unilaterally in 71% of occupants, bilaterally in 5.5% of occupants, and along the falx cerebri in 23.5% of occupants. In , the location of the injury is identified by crash type and by passenger location. The occurrence of coup and contrecoup type injuries are discussed further in this article.
Distribution of location of injury by (A) crash type and (B) occupant location.
The majority of the results for the simple linear regression analysis of the 57 cases were not statistically significant because of the small sample size. However, a few key variables proved statistically significant. Statistically significant (p-value<0.05) results and mildly significant (p-value<0.1) results are reported in . Additionally, the prediction intervals (PI) are reported in . These results show increases in SDH volumes, with higher delta-v/BES in frontal and near-side crashes. In near-side crashes, there was a mildly significant positive correlation between ISS and Cmax, as well as between ISS and delta-v/BES. Midline shift was significantly positively correlated with maximum crush in near-side crashes. Analysis of occupant position revealed a significantly positive correlation between delta-v/BES for drivers for all crash types and SDH volume. There was also a mildly significant positive correlation between delta-v/BES for drivers for all crash types and ISS. Of those occupants unbelted in frontal crashes, there was a mildly significant positive correlation observed between delta-v/BES and SDH volume, as well as between delta-v/BES and midline shift. No statistically significant correlation was observed for belted occupants. However, this may be because of the bias from recruiting 80% belted occupants in frontal collisions.
Statistically Significant (*) and Mildly Significant Results for the Simple Linear Regression Analysis of the Cases by Crash Characteristics
The resulting mean SDH volume in cases with airbag deployment was not compared using statistical tests because of the small sample sizes in each group; however, trends were observed with this data set (). Of the 57 occupants, 16 did not have airbag deployment from the available locations; none of the 8 occupants located in the back seat had airbag deployment. For drivers, the mean SDH volume was compared for the steering wheel airbag and roof-side rail airbag in frontal and near-side crashes. The mean SDH volume was decreased with the deployment of the steering wheel airbag in frontal crashes. The greatest decrease in mean SDH volume (5.12
cc) was in near-side crashes when the roof-side rail airbag deployed. This finding agrees with previous studies showing reduced brain injury severity with side airbag deployment.23,24
All certain, probable, and possible IPCs were considered when computing IPC incidence. The most frequent contacts that resulted in SDH in frontal crashes were the A-pillar and steering wheel. In a near-side crash, the most common contact to result in SDH was the window frame, followed by the roof. In a far-side crash, the most common contact was located on the opposite side of the vehicle. Contact with the door resulted in the highest number of SDHs in far-side crashes.
The resulting mean subdural hematoma (SDH) volume by crash type for airbag deployment. RSR, roof side rail airbag.
Age was of particular interest when analyzing the relationship among crash mechanics, occupant characteristics, and brain injury. For this analysis, two occupants, ages 16 and 29, were excluded for outlying SDH percentages of 4.4% and 3.35%, respectively. A mildy significant positive correlation was observed between SDH volume and age for near-side crashes as seen in . Twenty-nine of the 57 (51%) occupants had a midline shift. Of these, more than half (52%) sustained multiple intracranial injuries. For those drivers with midline shift, a mildly significant positive correlation was observed between midline shift and age in frontal crashes. The results of this analysis demonstrate a trend of increasing SDH volume with age. Four out of the five fatalities within this study had midline shift.
Statistically Significant (*) and Mildly Significant Results for the Simple Linear Regression Analysis of the Cases by Age and Glasgow Coma Scale (GCS)
The mean percent SDH volume and mean percent injured intracranial volume was greatest for far-side crashes, followed by near-side and then frontal crashes. Additionally, the location of the SDH varied by crash type. SDH was most frequently observed along the falx cerebri (43%) in frontal crashes. A coup-type injury was also frequently observed in frontal crashes (38%). A contrecoup type injury was more common in the near and far-side crashes (37% and 50%, respectively). A very small number of occupants sustained SDH along the falx cerebri for near and far-side crash types (10% and 8%, respectively). Bilateral SDH was observed only in those occupants in near-side crashes (15%). The right and left mean SDH volumes were nearly double compared with SDH volumes along the falx. Volumes of SDH were also greater when located posteriorly. Bilateral SDH volumes were lower than those isolated along the right, left, or along the falx cerebri.
Cranial vault fractures, basilar fractures, and a combination of both were observed in 17 occupants. Those occupants who sustained a combination of vault and basilar fractures had significantly greater midline shift than those with no skull fracture (p
=0.0318). Measurements of midline shift were greater for those occupants with multiple fractures than for those occupants with isolated basilar or vault fractures, which demonstrated a mild statistical significance (p
=0.0995 and p
=0.0669, respectively). Two out of the five MVC fatalities sustained a vault fracture. Midline shift has shown to be indicative of increased intracranial pressure because of mass effect, and this study supports this clinical assessment, as SDH volume is significantly positively correlated with midline shift (r2
<0.0001). As expected, there was a significantly negative correlation between lower GCS score at the crash site and greater percent SDH volume.11
A similar significantly negative correlation was observed between lower GCS score measured in the controlled setting of the emergency department and greater percent SDH volume. There was a mildly significant negative correlation between lower GCS score at the crash site and greater magnitude of midline shift.