Ruptured aneurysm associated with partially duplicated posterior communicating artery--case report.

A 65-year-old woman presented with a ruptured saccular aneurysm associated with a rare variation of the posterior communicating artery (PcoA), partially duplicated PcoA. The PcoA with this variation forked just distal to the aneurysmal neck, and the two branches independently merged into the posterior cerebral artery. Initial clipping failed to isolate the aneurysm from one of the two branches, so the aneurysmal dome continued to pulsate and bleed. Temporary clipping of the proximal internal carotid artery revealed the fork of the two branches just distal to the aneurysmal neck. A curved Yasargil clip was used to clip the aneurysm and preserve the PcoA and branches. Careful observation of this PcoA variation is needed because the arterial structures may be hidden by the thickened arachnoid membrane.