Synovial cyst of the transverse ligament of the atlas in a patient with osodontoideum and atlantoaxial instability

Study Design. A case report and review of the literature. Objective. To describe the diagnosis and successful treatment of a synovial cyst arising from the transverse ligament in a patient with os odontoideum and atlantoaxial instability. Summary of Background Data. Synovial cysts arising from the transverse liga ment of the atlas are extremely rare. Development of a synovial cyst is tho ught to be attributable to degenerative changes of the C1-C2 facet joints o r to microtrauma. Direct excision of the cyst is the only treatment cited i n previous reports. Methods. A synovial cyst arising from the transverse ligament of the atlas in a 45-year-old man with os odontoideum and atlantoaxial instability was t reated surgically with posterior atlantoaxial fusion alone. The magnetic re sonance images, surgical treatment, and related literature are reviewed. Results. Preoperative magnetic resonance images of the cervical spine showe d a large cystic mass located ventral to the cord arising at the level of t he transverse ligament of the atlas: the mass was of tow signal intensity o n T1-weighted images, was of high signal intensity on T2-weighted images, a nd was enhanced marginally with gadolinium-DTPA on T1-weighted images. Spon taneous regression of the cyst was identified on the follow-up magnetic res onance images taken 3 months after C1-C2 posterior wiring and fusion. Conclusions. A patient with a synovial cyst arising at the C1-C2 junction v entrally at the level of the transverse ligament showed spontaneous regress ion of the lesion after C1-C2 posterior wiring and fusion.