Radiographic Risk Factors and Surgical Outcomes for Retroodontoid Pseudotumors

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.