Immediate Reduction of a Retro-odontoid Synovial Cyst Following Lateral Atlantoaxial Joint Puncture and Arthrography: A Case Report.

STUDY DESIGN: Case report. OBJECTIVE: We report on a case with a retro-odontoid synovial cyst, and the immediate reduction of the cyst was confirmed after lateral atlantoaxial joint puncture and arthrography. SUMMARY OF BACKGROUND DATA: Retro-odontoid synovial cysts are rare diseases located posteriorly to a dense axis. Because 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. METHODS: A 52-year-old female presented with atlantoaxial instability. She complained of neck pain and numbness in her hands. Magnetic resonance imaging revealed a retro-odontoid synovial cyst. Lateral atlantoaxial joint puncture and arthrography were performed. RESULTS: Two days after treatment, the patient showed significant improvement in the numbness of her hands, and a follow-up magnetic resonance imaging revealed an immediate reduction in the cyst. During a 4.5-year follow-up period, no recurrence of the clinical symptoms occurred. CONCLUSION: 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. LEVEL OF EVIDENCE: N/A.