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Schemas of 4 different types of surgical treatments: remotely proximal parent artery occlusion (RPO), immediately proximal parent artery occlusion (IPO), clip reconstruction (CR), and distal bypass with or without branching artery occlusion (DB). Note that in RPO, collateral development extends from the external carotid system (arrowhead) or muscular branches of the extracranial vertebral artery (arrow) into the intracranial vertebral and basilar arteries.
