Supraclinoid internal carotid artery fenestration from which the posterior communicating artery arising with infundibular dilatation at its origin diagnosed by magnetic resonance angiography.

A 72-year-old man with vertigo underwent cranial magnetic resonance (MR) imaging and MR angiography using a 3.0-Tesla scanner. MR angiography showed an aneurysm-like lateral protrusion from the left supraclinoid internal carotid artery (ICA) and infundibular dilatation of the left posterior communicating artery at its origin. After creating both partial maximum-intensity-projection images and partial volume-rendering images, a fenestration of the supraclinoid ICA was found. The posterior communicating artery arose from the fenestrated segment, and its origin was dilated triangularly, indicating infundibular dilatation. Cerebral arterial fenestration is not so rare, but it is rarely found at the ICA. The majority of recently reported cases had an associated aneurysm at the proximal end of the fenestration diagnosed using three-dimensional rotational angiography (3DRA). MR angiography is noninvasive and widely used for the screening of cerebral arterial lesions. Even though 3.0-Tesla scanner, special resolution of MR angiography is much lower than that of the 3DRA. For the diagnosis and confirmation of this rare variation, partial maximum-intensity-projection images and/or partial volume-rendering images are useful.