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Pseudoocclusion of the left vertebral artery. The left vertebral artery appears occluded at its intracranial V4 segment during the arterial phase of mCTA (arrow in A). This is related to severe stenosis at its origin (D). The previously unopacified intracranial V4 segment is shown to enhance in the delayed phases of mCTA (arrows in B and C). If only single-phase CTA had been used (analogous to the arterial phase of the mCTA, A), a V4 segment occlusion would have been diagnosed.
