Double Origin of the Posterior Inferior Cerebellar Artery Diagnosed by MR Angiography: A Report of Two Cases.

The posterior inferior cerebellar artery (PICA) frequently arises from the fenestrated segment of the intracranial vertebral artery (VA), and this common variation can be misinterpreted as or confused with a PICA of double origin. Rarely, a PICA of true double origin occurs when two branches of the PICA arise separately from the intracranial VA and fuse to form an arterial ring. We discovered this rare variation incidentally while interpreting images of magnetic resonance (MR) angiography. This is the first report of MR angiographic findings of this rare variation.