The incidence of ischemic stroke reported after blunt vertebral artery injury is lower than that reported after blunt carotid artery injury. Unlike the carotid arteries, the vertebral arteries receive collateral blood flow through ascending cervical branches in addition to a convergent arterial supply with the contralateral vertebral artery. We hypothesize that the incidence of stroke after vertebral artery injury is less than after carotid artery injury in part because of reconstitution of vertebral arteries by cervical collaterals. A retrospective blinded interpretation of angiographic studies in 46 patients with blunt vertebral injury was performed to assess for presence and grade of vertebral artery injury and for the presence of reconstitution of the vessel via cervical collaterals. Follow-up CT scans from the same patients were evaluated for the presence of posterior circulation strokes. There were 55 injured vertebral arteries in the 46 patients, of whom 8 experienced posterior fossa strokes. Two-tailed Fisher exact probability test evaluating the hypothesis that patients with vertebral artery collaterals were less likely to experience posterior fossa strokes reached significance, p < 0.05. Of patients with occlusive (grades IV and V) injuries, those with collateral vessels were significantly less likely to experience posterior fossa strokes (p < 0.01). This result may be considered when weighing the potential risks and benefits of antiplatelet or anticoagulation therapy in patients with occlusive blunt vertebral artery injury.
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