Aneurysm of the distal posterior inferior cerebellar artery originating from the extracranial and extradural vertebral artery.

A 42-year-old woman presented with a ruptured aneurysm of the distal posterior inferior cerebellar artery (PICA), which had a rare extracranial and extradural origin. Medial suboccipital craniectomy and C-1 laminectomy were performed. The aneurysm had adhered to the right cerebellar tonsil, but was successfully clipped without difficulty. Intraoperatively, the PICA origin was recognized in the extracranial and extradural space between the dorsal roots of the C-1 and C-2 nerves. The origin of the PICA from the vertebral artery (VA) may occur at any portion of the VA from the site of penetration of the dura to the vertebrobasilar junction, but an extradural origin is uncommon. A ruptured aneurysm of the PICA branching from the VA at a site proximal to the vertebrobasilar junction and below the foramen magnum may be overlooked by three-vessel angiography if the contrast medium cannot reflux to the contralateral PICA origin.