Subarachnoid hemorrhage caused by ruptured dissecting aneurysm arising from the extracranial distal posterior inferior cerebellar artery--case report.

A 50-year-old man presented with a dissecting aneurysm arising from the extracranial portion of the right posterior inferior cerebellar artery (PICA) causing subarachnoid hemorrhage (SAH) and manifesting as sudden onset of disturbed consciousness. Computed tomography showed SAH with ventricular reflux predominantly in the posterior fossa. Angiography revealed a fusiform aneurysm of the right PICA originating extracranially from the right vertebral artery. The aneurysm was isolated and excised. Histological examination showed dissection of the aneurysm wall. Dissecting aneurysm arising from the extracranial portion of the PICA is extremely rare.