Retroodontoid synovial cyst
Neurosurgery Department, University General Hospital of Alicante, Foundation for the Promotion of Health and Biomedical Research in the Valencian Region (FISABIO), Alicante, Spain
Because the atlanto-dens joint is a synovial joint, its degeneration can lead to subchondral cyst formation and synovitis and predispose affected individuals to fracture 1).
Retro-odontoid cervical synovial cysts are rare diseases located posteriorly to a dense axis.
Attributable to degenerative changes in the atlantoaxial joints and atlantoaxial instability 2).
Association with Forestier’s disease has been reported in only one previous study. Cyst probably develop as a result of enhanced mechanical stress on the only remaining mobile joint. In the literature treatment of retro-odontoid mass associated with Forestier has usually involved occipito-cervical fusion with transoral decompression 3).
Although retro-odontoid synovial cysts remain rare, an increasing number have been reported in the literature. Affecting adults in the sixth decade of life, retro-odontoid synovial cysts produce slowly progressive upper spinal cord symptoms.
Most reports have focused on surgical treatment, only a few have examined nonsurgical treatment. However, several months are required after nonsurgical treatment until cyst regression.
A 52-year-old woman presented with atlantoaxial instability. She complained of neck pain and numbness in her hands. Magnetic resonance imaging (MRI) revealed a retro-odontoid synovial cyst. Lateral atlantoaxial joint puncture and arthrography were performed.
Two days after treatment, the patient showed significant improvement in the numbness of her hands, and a follow-up MRI revealed an immediate reduction in the cyst. Over a 4.5-year follow-up period, no recurrence of the clinical symptoms occurred.
Lateral atlantoaxial joint puncture may immediately reduce retro-odontoid synovial cysts, and the lateral atlantoaxial joint has a communication channel with the retro-odontoid synovial cyst via the atlantodental joint. Once disappearance of the cyst is confirmed, an acceptable long-term outcome can be achieved with nonsurgical treatment even in cases with atlantoaxial instability 6).