Dynamic axial brain stem distortion as a mechanism in the production of brain stem hemorrhages: role of the carotid arteries.

Dynamic axial distortion of the brain stem has long been recognized as occurring in the presence of supratentorial mass lesions. Although brain stem hemorrhages occur under these circumstances, the pathophysiology of these hemorrhages is still a matter of controversy. In the present study, the role of the carotid arteries in tethering the brain stem was evaluated during dynamic axial distortion of the neuraxis of the dog. Brain stem hemorrhages occurred in 32 of 48 dogs in which the carotid arteries were left intact (67%) and in only 9 of 46 animals in which the carotid arteries were sectioned (20%). The difference between the two groups is statistically significant (chi 2 = 19.3; P less than 0.001). In this study, we can eliminate intracranial pressure as the primary cause of the lesions because a single variable is present in one series and absent in the other, whereas intracranial pressure and its duration are kept constant. It is concluded that the tethering effect of the carotid arteries is a significant factor in the production of brain stem hemorrhages in the dog by dynamic axial distortion of the brain stem. A selective review of the literature on production of brain stem lesions is provided to support these findings.