Pericallosal artery aneurysm originating from a "supreme anterior communicating artery".

Report on the rare case of a ruptured pericallosal aneurysm originating from an atypic communicating segment between both distal A2 arteries, called the 'supreme anterior communicating artery'. The neurosurgeon should be aware of this rare vascular anomaly that might be angiographically occult and raise unexpected intraoperative difficulties.