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Eight cases of basal skull fracture with transverse fracture of the petrous temporal bone with medial extension to the internal carotid artery and lateral extension of the structures of the middle ear are described. Injuries in all cases were due to major blunt impact to the head usually occurring in a motor vehicle accident. General autopsy revealed major blood loss without any obvious external or internal site of hemorrhage suggesting that exsanguination was a complication of the head injury. The internal carotid arteries at the most medial extension of the fractures were lacerated or transected in all cases. In selected cases, the cervical internal carotid arteries were perfused and perfusate escaped rapidly from the ear(s) with the majority of fluid bypassing the cerebral venous system. Magnetic resonance image reconstruction of sequential sections of the fractured base of the skull confirmed the laceration of the internal carotid arteries and disruption of the middle ear. Based on this evidence, we propose that some displaced fractures of the base of the skull produce carotid-middle ear continuities which act as arterial shunts, resulting in rapid fatal exsanguination through the ear.

The mechanism for the preferential distribution of emboli to cerebral arterial bordcrzone regions, known to cause some watershed infarcts was studied. We hypothesized that emboli of a specific size range are selectively directed to the arterial borderzones due to the tendency of emboli to bypass the small arterial branches which emerge proximal to major borderzones. To test this hypothesis we perfused the brains of cadavers with suspensions of 90-210 µm glass microspheres and chemically extracted the particles from various arterial territories and a watershed zone. Particles in the 150-210 µm size range were found to be preferentially distributed to the watershed zone whereas particles less than 150 µm in size were randomly dispersed in leptomeningeal arteries of all vascular regions. To assess the role of branch size on the concentration of emboli at bifurcations, we perfused artificial analogs of evenly and unevenly branching bifurcations with suspensions of 90-150 µm and 150-210 µm particles. Branching cylinders with symmetrical branches contained the same concentration of particles, independent of particle size. In contrast, when one branch was one-quarter the size of the other, the concentration of 150-210 µm particles in the asymmetric branch was approximately 65% of the main trunk. Particles 90-150 µm in size were evenly distributed despite variation in branch size. These results indicate that emboli, of a limited range of size, may be selectively propagated to the distal ramifications of subarachnoid arteries located in the watershed zone rather than diverging into small calibre branches which arise along the way.