Synovial cyst of dens causing spinal cord compression. Case report.

We report a rare case of synovial cyst of the dens (odontoid process) in a 61 year old women with no previous history of trauma. She had progressive symptoms of 1 year's duration due to spinal cord compression. Magnetic resonance imaging of cervical spine revealed a large mass posterior to the dens which was compressing the spinal cord near the cervicomedullary junction. This lesion was at first considered radiologically to represent an exuberant pannus formation or a meningioma of the foramen magnum, but subsequent surgical intervention and pathological examination revealed that it was a synovial cyst. Similar cases reported in the literature are reviewed and discussed.