Synovial Cyst of the Transverse Ligament of the Atlas in a Patient With Os Odontoideum 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 ligament of the atlas are extremely rare. Development of a synovial cyst is thought to be attributable to degenerative changes of the C1–C2 facet joints or to microtrauma. Direct excision of the cyst is the only treatment cited in 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 treated surgically with posterior atlantoaxial fusion alone. The magnetic resonance images, surgical treatment, and related literature are reviewed.

Results. 

Preoperative magnetic resonance images of the cervical spine showed a large cystic mass located ventral to the cord arising at the level of the transverse ligament of the atlas: the mass was of low signal intensity on T1-weighted images, was of high signal intensity on T2-weighted images, and was enhanced marginally with gadolinium-DTPA on T1-weighted images. Spontaneous regression of the cyst was identified on the follow-up magnetic resonance images taken 3 months after C1–C2 posterior wiring and fusion.

Conclusions. 

A patient with a synovial cyst arising at the C1–C2 junction ventrally at the level of the transverse ligament showed spontaneous regression of the lesion after C1–C2 posterior wiring and fusion.