Duplicate origin of the posterior communicating artery diagnosed by magnetic resonance angiography.

Extremely rarely, a posterior communicating artery (PCoA) of "duplicate origin" occurs when two branches of the PCoA arise separately from the supraclinoid segment of the internal carotid artery (ICA) and quickly fuse to form an arterial ring. Three such cases previously reported were described as "fenestration." We report the case of this rare variation diagnosed by magnetic resonance angiography and discuss the differentiation of PCoA of duplicate origin from PCoA fenestration, supraclinoid ICA fenestration, and hyperplastic anterior choroidal artery.