Mallory 1 SUBDURAL HEMATOMA AND AGING: CRASH CHARACTERISTICS AND ASSOCIATED INJURIES

Among motor vehicle crash head injuries, subdural hematomas (SDH) are both frequent and lifethreatening, especially for older occupants. Previous research on the mechanism of injury and on the increased vulnerability of older individuals to SDH has focused on the failure of bridging veins, which are one possible source of subdural bleeding. For all age groups, the injury mechanism and injury tolerance for SDH as a result of other bleeding sources has not been addressed. In the current study, two US crash databases were used to compare crash and injury characteristics for SDH cases in different age groups, with a focus on the original source of bleeding. Review of cases from the Crash Injury Research and Engineering Network (CIREN) database showed that both bridging veins and bleeding sources other than bridging veins are responsible for SDH among crash occupants in all age groups. Analysis of weighted data from the National Automotive Sampling System Crashworthiness Data System (NASS CDS) showed that the frequency of isolated SDH increases with age, potentially reflecting an increase in the frequency of SDH caused by bridging vein bleeding, particularly in frontal crashes and among women. SDH accompanied by brain contusions or other potential bleeding sources on the surface of the brain are also common, especially in side impacts and among occupants younger than 70. These cases potentially represent injuries where subdural bleeding came from sources other than bridging veins. Improved definition of SDH injury tolerance for all adult occupants will require a better understanding of the mechanism of injury from sources other than bridging veins, but determination of SDH injury tolerance for older occupants should focus on evaluation of the increasing risk of bridging vein failure with age. INTRODUCTION Subdural hematoma (SDH) is a frequent and lifethreatening injury, especially for older adults. SDH has been reported in 26-36% of serious head injury cases [Gennarelli and Graham, 2005, Perel et al., 2009] and is reported to be among the most frequent injuries seen by neurosurgeons [Taussky et al., 2008]. Mortality rates are reported from 33 to 79% [Sawauchi and Abe, 2008, Servadei, 1997, Taussky et al., 2008]. For older occupants, SDH presents doubly-increased risks since it is not only more frequent among older individuals [Mallory, 2010, Seelig et al., 1981] but also presents an increasing rate of mortality and poor outcome with increasing age [Hanif et al., 2009, Hukkelhoven et al., 2003, Raju et al., 2004, Stitzel et al., 2008]. SDH are collections of blood that form in the dural border cell layer between the dura and arachnoid [Haines et al., 1993] or between the dura and the pial surface of the brain [Miller and Statham, 2000]. The original source for the bleeding that produces SDH can be from adjacent brain contusions, lacerations or intracerebral hematomas; from ruptured cortical vessels on the surface of the brain; or from the bridging veins that cross the meninges en route to the dural sinuses [Depreitere et al., 2006, Graham, 1996, Lee et al., 1987, Miller et al., 1996, Miller and Statham, 2000, Toyama et al., 2005]. Although ruptured bridging veins are generally believed to be a major source of SDH [Gennarelli and Thibault, 1982, Gennarelli and Graham, 2005, Lee and Haut, 1989], post-mortem studies of fatal traumatic subdural cases showed that as many as two thirds of SDH were the result of brain contusions [Maxeiner, 1997]. In the remaining third of cases, bleeding was attributed to bridging vein rupture and torn cortical arteries with