Extracranial aneurysm of the posterior inferior cerebellar artery.

Aneurysms of the posterior inferior cerebellar artery (PICA) are rare, and may arise in unusual locations due to the complex and variable anatomy of this artery. The PICA does not usually originate from the extracranial vertebral artery. Of the few reported extracranial PICA aneurysms, all affected the distal segment. We describe an unusual extracranial PICA-vertebral artery (VA) junction aneurysm.