title: Radiographic analysis of the cervical spine in patients with retro-odontoid pseudotumors.
abstract: METHODS
  A retrospective review of 10 consecutive patients with a noninflammatory retro-odontoid pseudotumor.
  
  
  OBJECTIVE
  To examine the radiographic characteristics in patients with a retro-odontoid pseudotumor and to evaluate the efficacy of posterior fusion.
  
  
  BACKGROUND
  A retro-odontoid pseudotumor, a reactive fibrocartilaginous mass, is known to develop after chronic atlantoaxial instability; however, one-third of the reported cases showed no overt atlantoaxial instability. The pathomechanism for such "atypical" cases remains unclear, although altered cervical motion secondary to ossification of the anterior longitudinal ligament (OALL) or severe spondylosis has been implicated.
  
  
  METHODS
  We reviewed the charts and radiographs of 10 patients with a retro-odontoid pseudotumor who underwent surgery. Preoperative radiographs were evaluated for atlas-dens interval (ADI), presence of OALL, range of motion, and segmental motion adjacent to the atlantoaxial joint. Computed tomography was evaluated for degenerative changes of zygapophysial joints.
  
  
  RESULTS
  There were 6 men and 4 women. Atlantoaxial instability (ADI >4 mm) was observed in 2 patients. ADI was less than 3 mm in 5 patients. Frequent association of OALL (6 patients) and marked decrease in C2 to C7 range of motion (mean, 17.6 degrees ; range, 3 degrees-36 degrees ) were noted. Ankylosis of O-C1 was observed in 4 patients and C2 to C3 in 6. Severe degenerative change of C2 to C3 zygapophysial joint was observed in 4 patients. The patients underwent occipito-cervical fusion (9 patients) or direct removal of the pseudotumor (1 patient). Postoperative magnetic resonance imaging invariably demonstrated the mass regression.
  
  
  CONCLUSIONS
  Retro-odontoid pseudotumors were not always associated with radiographic atlantoaxial instability. Our data indicate that extensive OALL and ankylosis of the adjacent segments are risk factors for the formation of the pseudotumor. Retro-odontoid pseudotumors may develop as an "adjacent segment disease" after altered biomechanics of the cervical spine, especially those in the adjacent segments. Posterior fusion was effective even in cases without radiographic atlantoaxial instability.
authors.affiliation: Department of Orthopaedic Surgery, Faculty of Medicine, the University of Tokyo, Tokyo, Japan. chikuda-tky@umin.ac.jp
authors.forename: Hirotaka
authors.initials: H
authors.lastname: Chikuda
authors.forename: Atsushi
authors.initials: A
authors.lastname: Seichi
authors.forename: Katsushi
authors.initials: K
authors.lastname: Takeshita
authors.forename: Naoki
authors.initials: N
authors.lastname: Shoda
authors.forename: Takashi
authors.initials: T
authors.lastname: Ono
authors.forename: Ko
authors.initials: K
authors.lastname: Matsudaira
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Kawaguchi
authors.forename: Kozo
authors.initials: K
authors.lastname: Nakamura
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001268:Atlanto-Axial Joint / Q000000981:diagnostic imaging* / Q000473:pathology / Q000503:physiopathology; D002574:Cervical Vertebrae / Q000000981:diagnostic imaging* / Q000473:pathology / Q000503:physiopathology; D005260:Female; D006104:Granuloma, Plasma Cell / Q000000981:diagnostic imaging* / Q000473:pathology / Q000503:physiopathology; D006801:Humans; D006984:Hypertrophy / Q000000981:diagnostic imaging / Q000473:pathology / Q000503:physiopathology; D007091:Image Processing, Computer-Assisted; D008022:Ligaments / Q000000981:diagnostic imaging / Q000473:pathology / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D009809:Odontoid Process / Q000000981:diagnostic imaging* / Q000473:pathology / Q000503:physiopathology; D011859:Radiography; D011871:Radiology / Q000379:methods; D016059:Range of Motion, Articular / Q000502:physiology; D012189:Retrospective Studies; D013115:Spinal Canal / Q000000981:diagnostic imaging / Q000473:pathology / Q000503:physiopathology; D013117:Spinal Cord Compression / Q000000981:diagnostic imaging* / Q000473:pathology / Q000503:physiopathology; D013122:Spinal Diseases / Q000000981:diagnostic imaging* / Q000473:pathology / Q000503:physiopathology; D013123:Spinal Fusion / Q000295:instrumentation / Q000379:methods; D016896:Treatment Outcome