Incidental Identification of an Intracranial Vertebral Artery Aneurysm Related to Unilateral Vertebral Artery Occlusion in a Patient With a Ruptured Internal Carotid-Posterior Communicating Artery Aneurysm: A Case Report.

An intracranial aneurysm located on the vertebral artery (VA) following unilateral VA occlusion is rare. Little has been described about this entity. An 85-year-old drowsy woman was transported to our hospital. A screening CT scan showed subarachnoid hemorrhage and secondary acute hydrocephalus. CT angiography revealed a right internal carotid-posterior communicating (IC-Pcom) artery aneurysm, an intracranial VA aneurysm, and left VA occlusion. The intracranial VA aneurysm was located on the lateral side of the left VA, near the origin of the anterior spinal artery. Following external ventricular drainage for acute hydrocephalus, the ruptured IC-Pcom aneurysm was obliterated with endovascular embolization. The intracranial VA aneurysm was not treated because of the complicated access route. The procedure was performed without any intraoperative complications. However, the patient died nine days after surgery because of global cerebral ischemia. Initial brain injury or rupture of the untreated intracranial VA aneurysm was suspected. We describe a rare case of an intracranial VA aneurysm that may have formed after unilateral VA occlusion.