Postoperative regression of retro-odontoid pseudotumor after atlantoaxial posterior fixation

Abstract

Purpose: To investigate the incidence of retro-odontoid pseudotumor in patients with atlantoaxial instability (AAI) and evaluate pseudotumor regression after posterior fixation.

Materials and Methods: From July 2004 to August 2015, 175 patients with AAI underwent posterior fixation operations at our institution. After excluding 11 patients (previous operation, n = 4

history of tumor, n = 7), the final study population comprised 164 patients. The final study population was categorized according to their underlying diseases (rheumatoid arthritis [RA], os odontoideum, atlanto-occipital assimilation, dens fracture, AAI of unknown cause, etc.) and age (adult and pediatric groups). The incidence of retro-odontoid pseudotumor in each group was analyzed. Pre- and postoperative magnetic resonance or computed tomography images were reviewed to assess its regression following surgery.

Results: Of the 164 patients included, 38 had retro-odontoid pseudotumor (23.2%). Three were diagnosed with RA and the rest were non-RA patients including os odontoideum (n = 12), dens fracture (n = 6), atlanto-occipital assimilation (n = 4), Morquio syndrome (n = 1), and AAI of unknown cause (n = 12). Pseudotumor size regressed in all 38 patients after atlantoaxial posterior fixation. There was a statistically significant decrease in pseudotumor size (the length between the anterior border of the odontoid process to the posterior border of the pseudotumor) from a mean length of 17.7 mm to 14.9 mm (P < 0.001).

Conclusions: The patients had various underlying diseases and the overall incidence of retro-odontoid pseudotumor in patients with symptomatic AAI was 23.2% at our institution during the past 11 years. All patients who underwent posterior fixation for AAI showed a statistically significant decrease in pseudotumor size.