Fracture of the anterior arch of the atlas is a rare complication of foramen magnum decompression(FMD)for Chiari malformation. We report a case of a fracture of the anterior arch of the atlas after FMD. A 42-year-old woman was referred to our hospital from a nearby clinic where Chiari malformation and syringomyelia were incidentally detected during head magnetic resonance imaging (MRI)examination for headache. We performed FMD and tonsillectomy for the Chiari malformation. The patient had an

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... ventful postoperative course and was in good condition when discharged. She developed neck pain without any preceding incident approximately 7 months after surgery. Subsequently, she experienced neck pain during flexion, extension, and sneezing. Neck computed tomography(CT)performed at a nearby clinic revealed a fracture of the anterior arch of the atlas, and she was referred to our hospital once again. Although neck radiography did not confirm an instability of the craniocervical junction, the neck pain progressed;thus, posterior atlantoaxial fusion was performed. Due to the thinning of the C2 vertebral pedicles, part of the C2 vertebral arch was removed during FMD, and pars screws were inserted into the C2 vertebra with lateral mass screws inserted into the C1 vertebra. The subsequent postoperative course was uneventful. Three cases have been reported in the literature, and the mechanism of injury(e.g., trauma)was not confirmed in all of them. Posterior fusion was used in 2 cases, external immobilization with a halo vest was used in 1 case, and fracture healing was achieved with a good prognosis in all three cases. When neck pain develops a few months after FMD, fracture of the anterior arch of the atlas should be suspected and preferably confirmed using CT. (Received:November 18, 2019;accepted:February 4, 2020) Key words anterior arch fracture of the atlas, foramen magnum decompression, Chiari malformation *1 大森赤十字病院脳神経外科/Department of Neurosurgery, Omori Red Cross Hospital 連絡先:〒143-8527 大田区中央 4-30-1 大森赤十字病院脳神経外科 佐野 透 〔Address reprint requests to:Tohru Sano, M