Hypoplasia of the internal carotid artery with associated fenestration and extremely long P1 segment of the ipsilateral posterior cerebral artery diagnosed by MR angiography.

We present what we believe is the first report of a patient with unilateral hypoplasia of the internal carotid artery with associated ipsilateral anomalous posterior cerebral artery, extremely long and fenestrated P1 segment that was diagnosed on magnetic resonance (MR) angiography. Careful review of MR angiographic images is important to detect rare arterial variations, and partial maximum-intensity-projection images aid their identification on MR angiography.