Traumatic rupture of the circle of Willis with closed head injury: Its pathology and possible pathogenesis.

Massive and fatal subarachnoid hemorrhage (SAH) with an injury on the circle of Willis may be caused by blunt force to the head; however, it is extremely rare, and the precise mechanism of arterial rupture remains unclear. We investigated the clinicopathologic appearance of four rare autopsy cases of massive SAH associated with the rupture of the circle of Willis. All four cases were men aged 17-75 years who presented with a loss of consciousness within a short interval after the injury. Autopsy revealed that the rupture site was located in the vertebral artery in two cases and in the anterior cerebral artery (ACA) in two cases. During our literature review, we found no previous report on traumatic ACA rupture. Based on the correlation of the autopsy findings and the circumstance of injury, we determined that the accidental excessive stretching of the selected artery by neck anteflexion or rotation after a blunt trauma to the posterior head might have caused this rare lethal injury. These cases demonstrated the diversity of the traumatic rupture site of the circle of Willis after a blunt head and/or neck injury. The topographical features of the circle of Willis, particularly in correlation with the surrounding tissue, might account for the occurrence and site of these rare injuries.