Fenestration of the supraclinoid internal carotid artery arising from the paraclinoid aneurysmal dilatation and fusing with the origin of the posterior communicating artery: a case report.

We report an extremely rare case of fenestration of the supraclinoid internal carotid artery (ICA) diagnosed by magnetic resonance (MR) angiography. The smaller channel arose from the paraclinoid ICA aneurysmal dilatation, and the posterior communicating artery arose from the distal end of the fenestration. Careful observation of MR angiographic images, including source images, is important to detect rare arterial variations, and their identification on MR angiography is aided by the creation of partial maximum-intensity-projection images and partial volume-rendering images.