ABSTRACT
Vertebral artery injuries associated with C1 lateral mass screw insertion rarely occur during C1-2 fusion. The posterior inferior cerebellar artery (PICA) is uncommonly located at the C1 lateral mass insertion position. A 71-year-old woman with atlanto-axial subluxation and cord compression underwent C1-2 fusion. Sixth nerve palsy and diplopia were detected postoperatively, and decreased consciousness occurred on postoperative day 4. Brain magnetic resonance image (MRI) and computed tomography (CT) revealed PICA infarction. In the preoperative CT angiography, the PICA originated between the C1 and C2 level. In the postoperative CT scan, the PICA was not visible. The patient was treated conservatively for two weeks and recovered. PICA originating between the C1 and C2 level comprises 1.1–1.3% of cases. Therefore, vertebral artery anomalies should be evaluated prior to C1-2 fusion to prevent vessel injuries.