Abstract
BACKGROUND: An occipital artery-vertebral artery (OA-VA) anastomosis is rarely observed on cerebral angiography. The authors present a case of posterior circulation infarction during carotid artery stenting (CAS) due to an OA-VA anastomosis. OBSERVATIONS: A 73-year-old male presented with mild right internal carotid artery (ICA) stenosis, which progressed to near occlusion over 18 months. Cerebral angiography revealed anterograde flow from the external carotid artery (ECA) to the vertebrobasilar system via the OA-VA anastomosis, which was not recognized by the surgeons before treatment. CAS using a flow reversal technique was performed to prevent distal embolization in the ICA. MRI the day after CAS revealed cerebral infarcts in both cerebellar hemispheres and on the right side of the pons, possibly due to emboli that migrated via the OA-VA anastomosis into the ECA during CAS. LESSONS: As ICA stenosis progresses, an OA-VA anastomosis that was initially invisible on cerebral angiography may become apparent. Since this anastomosis can serve as a pathway for embolic migration during CAS, which can lead to posterior circulation infarction, it is essential to perform CAS in a manner that prevents embolic migration into the ECA in patients with OA-VA anastomoses. https://thejns.org/doi/10.3171/CASE25187.