Fatal vertebral artery pseudoaneurysm following intracranial migration of an odontoid screw: illustrative case.

backgroundIntracranial migration of odontoid screws is an exceedingly rare complication following anterior odontoid fixation. When such migration involves vital neurovascular structures, the consequences can be catastrophic. Although anterior odontoid screw fixation (AOSF) is generally well tolerated and biomechanically favorable, hardware failure leading to vertebral artery (VA) injury is sparsely reported. OBSERVATIONS: The authors present the case of a 79-year-old man who previously underwent AOSF for a type II odontoid fracture. He presented with acute neck pain after lifting a heavy object and was found to have cranial migration of the odontoid screw into the foramen magnum, causing mass effect on the right VA and a premedullary subarachnoid hemorrhage. After multidisciplinary evaluation, the patient underwent successful removal of the screw with anterior cervical exposure, followed by intraoperative detection and embolization of a right V4 segment VA pseudoaneurysm using overlapping flow diverter stents. Despite initial neurological stability, he developed respiratory decline and sepsis and ultimately died of multiorgan failure. LESSONS: This case highlights the importance of long-term surveillance following spinal instrumentation, the value of multidisciplinary coordination in managing complex neurovascular complications, and the fact that procedural success does not always guarantee favorable clinical outcomes in older, comorbid patients. https://thejns.org/doi/10.3171/CASE25538.