title: Radiographic risk factors and surgical outcomes for retroodontoid pseudotumors.
abstract: METHODS
  Retrospective review.
  
  
  OBJECTIVE
  The aim of this study is to assess the radiographic characteristics of patients with a retroodontoid pseudotumor and to evaluate the efficacy of posterior fusion.
  
  
  BACKGROUND
  Retroodontoid pseudotumors are usually caused by chronic atlantoaxial instability in patients with rheumatoid arthritis (RA). However, the pathomechanism and optimum treatment are unknown.
  
  
  METHODS
  We reviewed the charts and radiographs of 11 patients (5 RA and 6 non-RA) with a retroodontoid pseudotumor who underwent posterior fusion. Preoperative radiographs were evaluated for atlantodental interval; Redlund-Johnell criterion; O-C1, C1-2, C2-3, and C2-7 angles. The Japanese Orthopaedic Association (JOA) score was used to evaluate clinical outcomes.
  
  
  RESULTS
  All RA patients and 1 non-RA patient displayed atlantoaxial subluxation. Three patients underwent occipitocervical fusion and 8 patients atlantoaxial fusion. The JOA score improved significantly from 10.0 to 12.8 at follow-up (P<0.01). The retroodontoid pseudotumor regressed in 10 patients. Maximal thickness of the pseudotumor decreased from 8.9 mm preoperatively to 5.3 mm (P<0.01) at follow-up. In non-RA patients, the mean differences (Δ) between flexion and extension were 7.8, 13.4, 3.5, and 18.5 degrees for ΔO-C1, ΔC1-2, ΔC2-3, and ΔC2-7, respectively.
  
  
  CONCLUSIONS
  In RA patients, a retroodontoid pseudotumor may develop because of atlantoaxial subluxation. In non-RA patients, excessive atlantoaxial angular motion because of the limited range of motion of O-C1 and/or subaxial vertebra may cause a pseudotumor. Atlantoaxial fusion to suppress atlantoaxial instability is one of the optimum treatments.
authors.affiliation: Department of orthopaedic Surgery, Kurashiki Central Hospital, Okayama, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Sono
authors.forename: Eijiro
authors.initials: E
authors.lastname: Onishi
authors.forename: Mutsumi
authors.initials: M
authors.lastname: Matsushita
mesh_terms: D000368:Aged; D001268:Atlanto-Axial Joint / Q000000981:diagnostic imaging / Q000473:pathology / Q000601:surgery; D005260:Female; D006801:Humans; D007564:Japan; D007593:Joint Instability / Q000000981:diagnostic imaging / Q000601:surgery; D008297:Male; D008875:Middle Aged; D009369:Neoplasms / Q000000981:diagnostic imaging* / Q000601:surgery*; D009809:Odontoid Process / Q000000981:diagnostic imaging* / Q000601:surgery*; D011300:Preoperative Care; D011859:Radiography; D012307:Risk Factors; D016896:Treatment Outcome