title: Immediate Reduction of a Retro-odontoid Synovial Cyst Following Lateral Atlantoaxial Joint Puncture and Arthrography: A Case Report.
abstract: METHODS
  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.
  
  
  BACKGROUND
  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.
  
  
  CONCLUSIONS
  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.
  
  
  METHODS
  N/A.
authors.affiliation: From the Department of Orthopedic Surgery, Japanese Red Cross Society, Himeji Hospital, Hyogo, Japan.
authors.forename: Daisuke
authors.initials: D
authors.lastname: Ikegami
authors.forename: Takashi
authors.initials: T
authors.lastname: Matsuoka
authors.forename: Yasuaki
authors.initials: Y
authors.lastname: Aoki
mesh_terms: D001268:Atlanto-Axial Joint / Q000000981:diagnostic imaging* / Q000473:pathology / Q000503:physiopathology; D004322:Drainage / Q000379:methods*; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008875:Middle Aged; D009809:Odontoid Process / Q000000981:diagnostic imaging* / Q000473:pathology / Q000503:physiopathology; D011237:Predictive Value of Tests; D020127:Recovery of Function; D013129:Spinal Puncture; D013581:Synovial Cyst / Q000000981:diagnostic imaging* / Q000473:pathology / Q000503:physiopathology / Q000628:therapy*; D013997:Time Factors; D014057:Tomography, X-Ray Computed; D016896:Treatment Outcome