A Treated Case of Internal Carotid Artery Stenosis Associated with an Occipital Artery Originating from the Internal Carotid Artery.

Objective: The occipital artery (OA) typically originates from the external carotid artery; however, rare anatomical variants exist in which it arises from the internal carotid artery (ICA). Because the OA generally has anastomoses with the deep cervical and vertebral arteries, the OA in the present case, which originated from the ICA, functioned as a collateral pathway in the setting of ICA stenosis due to this unique anatomical variant. Furthermore, it may represent a potential embolic route during carotid artery stenting (CAS). We report the hemodynamic characteristics of and treatment strategy for the present case. Case Presentation: A 65-year-old man was found to have carotid artery stenosis during a routine brain screening and was referred to our department (Department of Neuroendovascular Therapy, Yokohama Municipal Citizen's Hospital) for further evaluation. Cerebral angiography and CTA revealed severe stenosis of the right ICA, as well as a collateral pathway through which blood flowed retrogradely from the deep cervical artery through the OA into the distal segment of the stenotic ICA. It was considered that an OA, which originally arose from the ICA, had changed to retrograde flow as a collateral pathway following the development of ICA stenosis. Because distal protection alone was deemed insufficient for embolic prevention, CAS was performed under flow reversal with occlusion of the common carotid artery, ICA, and external carotid artery, and the procedure was completed without major complications. Conclusion: In cases of ICA stenosis accompanied by an OA originating from the ICA, individualized embolic protection strategies based on detailed anatomical and hemodynamic evaluation are essential, with careful consideration of the risk of embolization via collateral pathways.