Fusiform aneurysm associated with fenestration of the posterior communicating artery.

A 62-year-old male presented with a rare case of fenestration of the supraclinoid segment of the internal carotid artery (ICA) at the origin of the posterior communicating artery (PCoA). The patient had a fusiform aneurysm at the proximal branch of the PCoA, which was successfully clipped, sparing the anterograde blood flow. The double origin and fenestration of the PCoA branching off at the C(2) segment of the left ICA suggested that this anomalous fenestration might have developed as the origin of the PCoA rather than the supraclinoid ICA during the early embryonal stage.