Postoperative changes in location and size of retro-odontoid pseudotumor after upper cervical fusion without decompression

Abstract

Purpose To evaluate the immediate postoperative changes in retro-odontoid pseudotumor (ROP) classified according to morphological characteristics following upper cervical fusion without decompression. Method This retrospective study analyzed 35 patients who underwent upper cervical fusion (C1-2 or occiput-cervical) for ROP between January 2020 and December 2023. ROPs were classified into solid and non-solid (mixed/cystic) types based on MRI signal characteristics. Radiological parameters including space available for cord (SAC), anterior atlantodental interval (AADI), and spinal cord compression were measured pre- and postoperatively. Clinical outcomes were assessed using visual analog scale (VAS), Japanese Orthopedic Association (JOA) score, and neck disability index (NDI). Results The cohort comprised 15 patients with non-solid masses and 20 with solid masses. Non-solid masses demonstrated significantly greater SAC improvement (3.01 +/- 1.81 mm vs. 0.94 +/- 1.66 mm, p < 0.001) and AADI correction (3.25 +/- 1.60 mm vs. 0.85 +/- 1.67 mm, p < 0.001) compared to solid masses. All non-solid cases showed postoperative fluid migration (53.3% upward, 46.7% posterior), with no difference in outcomes based on migration direction. Both groups achieved comparable clinical improvements with improvement rates of 80.33% versus 82.0% respectively (p = 0.73). Conclusions Non-solid ROPs exhibit superior radiological response to fusion without decompression compared to solid masses, likely reflecting their more reactive nature. Fluid migration following fusion represents a benign phenomenon that does not compromise clinical outcomes. These findings support fusion alone as an effective treatment strategy for appropriately selected patients with ROPs, particularly those with fluid-containing lesions.