Craniocervical junction synovial cyst associated with atlanto-axial dislocation--case report.

A 51-year-old female presented with a rare case of synovial cyst at the cruciate ligament of the odontoid process associated with atlanto-axial dislocation, manifesting as a history of headache and numbness in her left extremities for 5 months, and progressive motor weakness of her left leg. Neuroimaging studies revealed a small cystic lesion behind the dens, which severely compressed the upper cervical cord, and atlanto-axial dislocation. The cyst was successfully removed via the transcondylar approach. C-1 laminectomy and foramen magnum decompression were also performed. Posterior craniocervical fusion was carried out to stabilize the atlanto-axial dislocation. The cyst contained mucinous material. Histological examination detected synovial cells lining the fibrocartilaginous capsule. Synovial cysts of this region do not have typical symptoms or characteristic radiographic features. Careful preoperative evaluation of the symptoms and a less invasive strategy for removal of the cyst are recommended.