Right posterior communicating artery arising from the extreme proximal internal carotid artery, paraclinoid segment, diagnosed by magnetic resonance angiography.

purposeTo describe a case of right posterior communicating artery (PCoA) arising from the extreme proximal internal carotid artery (ICA), paraclinoid segment, diagnosed by magnetic resonance angiography (MRA).

methodsAn 80-year-old woman with subacute hemorrhagic infarction of the right basal ganglia underwent MRA using a 3-Tesla scanner. MRA was performed using a standard 3-dimensional time-of-flight technique.

resultsMRA of the intracranial region revealed no pathological lesions. A right fetal-type posterior cerebral artery (PCA) was observed. The hyperplastic right PCoA arose from the paraclinoid segment of the ICA, just distal to the origin of the ophthalmic artery, which is an extremely proximal point relative to the usual point at which it arises.

conclusionThe PCoA usually arises from the supraclinoid segment of the ICA, just proximal to the origin of the anterior choroidal artery. The PCA, which is mainly supplied by ICA, is called a fetal-type PCA, and there is a hyperplastic PCoA. Extremely rarely, the PCoA arises from a fenestration of the supraclinoid ICA. In such cases, the PCoA arises from the extremely proximal point of the ICA if the distal segment of the fenestration regresses. To our knowledge, no similar cases have been reported in the relevant English-language literature. Although the image quality of MRA is insufficient, careful observation of the source images and creation of volume-rendering MRA images are important for the correct diagnosis of this extremely rare variation.