Imaging Characteristics of Nonrheumatoid Arthritis Patients With Retro-odontoid Pseudotumor: A Multicenter Case-control Study.

ABSTRACT

STUDY DESIGN: Multicenter case-control study. OBJECTIVE: To identify imaging characteristics of the cervical spine in patients with retro-odontoid pseudotumor (ROP) without rheumatoid arthritis (RA) and determine the pathogenesis of ROP. BACKGROUND: ROP results from proliferative changes in the soft tissue of the atlantoaxial junction surrounding the region of the transverse ligament, and is commonly seen in RA patients. However, the pathogenesis of ROP caused by mechanical instability of the upper cervical spine in patients without RA is yet to be explained. MATERIALS AND METHODS: We collected imaging data [preoperative radiographs, magnetic resonance imaging (MRI), and computed tomography (CT)] of patients who underwent surgery between April 2011 and March 2022 at the three university hospitals for ROP (cases) and cervical spondylotic myelopathy (as age, sex, and institution matched controls). The two groups were compared for different parameters on cervical dynamic radiographs, MRI, and CT. RESULTS: The ROP group consisted of 42 patients, and the control group comprised 168 patients. C2-C7 range of motion was significantly smaller in the ROP group (25.8 ± 2.6°) compared with the control group (33.0 ± 1.0°). C2-C7 sagittal vertical axis was significantly larger in the ROP group than the control group (39.3 ± 3.6 vs. 32.2 ± 1.3 mm). MRI and CT assessment showed progressive degeneration at all intervertebral levels in the ROP group. A significant positive correlation was observed between the thickness of the soft tissue posterior to the dental process and the atlantodental interval in the flexion position ( r = 0.501). CONCLUSIONS: The development of ROP was associated with degeneration of facet joints and intervertebral disks in the middle and lower cervical spine. Our findings suggest that decreased mobility of the middle and lower cervical spine may cause instability in the upper cervical spine, leading to the formation of ROP.