環椎後頭骨癒合症の 2 例

Assimilation of the atlas is a rare disease, and this condition is characterized by a partial or complete congenital union between the atlas and the base of the occiput. We report two cases of assimilation of the atlas.A 32-year-old male had been suffering from neck stiffness, progressive numbness of the extremities and walking disturbance since he was 13 years old. Assimilation of the atlas associated with atlantoaxial instability was seen and spinal cord was compressed at the atlanto-occiput junction severely on MRI. Removal of the posterior arch of the atlas and occipito-cervical fusion was pertormed using instruments and the symptoms improved.A 51-year-old female lost consciousness which driving and collided into a concrete fence. She regained consciousness after a few minutes but experienced walking disturbance and right hand numbness. No intracranial lesion was found but MRI indicated a high signal area in the spinal cord at the occpitocervical junction. In addition to spinal cord injury, computed tomography revealed assimilation of the atlas, atlantoaxial subluxation, and os odontoideum. Loss of consciousness was considered resulting from vertebral artery insufficiency. After more or less the same surgery as the previous case, she could leave the hospital by walking and lead daily life without difficulties.