[An Extracranial Aneurysm in the Distal Posterior Inferior Cerebellar Artery Located at the Tonsillomedullary Segment:Case Report and Review of the Literature].

We report a rare case of subarachnoid hemorrhage(SAH)due to ruptured extracranial aneurysm originating at the caudal loop of the left posterior inferior cerebellar artery(PICA). A 50-year-old woman presented with severe headache and mild consciousness disturbance. Computed tomography(CT)revealed SAH and intraventricular hemorrhage. Vertebral angiography showed an extracranial aneurysm located on the tonsillomedullary segment of the left PICA. During the surgery, no vessel branches were confirmed near the aneurysm, and the aneurysm was successfully clipped through suboccipital craniotomy with C1 laminectomy. The patient showed significant recovery and was discharged without neurological deficit.