We report a case of ruptured flow-related aneurysm that appeared on the collateral channel between the proximal portion of the occluded vertebral artery (VA) due to dissection and the posterior inferior cerebellar artery (PICA). A 51-year-old man was admitted to our hospital with complaints of sudden left neck pain and vertigo at X years. On admission, anterior inferior cerebellar artery (AICA) syndrome was observed, and imaging scans demonstrated a left cerebellar hemispheric infarction

more »

... to left VA occlusion due to VA dissection. The patient was treated with antiplatelet drugs and discharged with left hearing loss. Periodic outpatient magnetic resonance imaging (MRI) scans were performed, and the MRI findings demonstrated a left VA occlusion that persisted for 3 years. At X+3 years, the patient suddenly presented with nausea, vomiting, dizziness, and neck pain, followed by loss of consciousness. On admission, subarachnoid hemorrhage (SAH) was observed on head computed tomography (CT). Cerebral angiography demonstrated a left VA occlusion at the proximal portion of the PICA and a flow-related aneurysm that formed on the collateral artery between the V3 portion and the PICA. Emergency aneurysmal trapping was performed without any new neurological deficits. He recovered to a Modified Rankin Scale (mRS) of 2 and was discharged on the 66 th day after admission. Flow-related aneurysm formation on the collateral channel after VA occlusion due to dissection is a rare complication; however, it should be noted during follow-up.