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Radiographic Risk Factors and Surgical Outcomes for Retroodontoid Pseudotumors

Sono, Takashi MD; Onishi, Eijiro MD, PhD; Matsushita, Mutsumi MD, PhD

doi: 10.1097/BSD.0b013e318299f4d8
Original Articles

Study Design: 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.

Summary of Background Data: 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.

Department of orthopaedic Surgery, Kurashiki Central Hospital, Okayama, Japan

The authors declare no conflict of interest.

Reprints: Eijiro Onishi, MD, PhD, Department of Orthopaedic Surgery, Kobe City Medical Center General Hospital, 2-1-1, Minamimachi, Chuouku Minatojima, Kobe city, 650-0047, Japan (e-mail:

Received January 7, 2013

Accepted April 21, 2013

© 2014 by Lippincott Williams & Wilkins, Inc.