case_images: PMC9610150_01
case_images: (a) MRI showed retro-odontoid mass with intramedullary T2-weighted image high signal. (b) Three-dimensional computed tomography (3D-CT) findings at craniocervical junction showed C1 assimilation and C2-3 fused vertebrae.
case_images: SNI-13-480-g001.jpg
case_images: PMC9610150_01_SNI-13-480-g001.jpg
case_images: F1
case_images: T2 high cord signal [Figure 1a]. The 3D-CT at the CCJ showed C1 assimilation and congenital Klippel-Feil fusion of the C2-3 vertebrae [Figure 1b].
case_images: Dynamic X-ray showed no obvious radiological instability with an atlantodental interval of 3.5 mm, but an instability angulation with a range of motion of 20 .
case_images: SNI-13-480-g002.jpg
case_images: PMC9610150_01_SNI-13-480-g002.jpg
case_images: F2
case_images: Dynamic X-rays showed no frank instability, but the atlantodental interval (ADI) was 3.5 mm, with 20  of angulation [Figure 2].
case_images: (a) Intraoperative findings and postoperative X-ray show occiput-cervical fixation. (b) MRI after three months surgery showed a reduction in ROPT.
case_images: SNI-13-480-g003.jpg
case_images: PMC9610150_01_SNI-13-480-g003.jpg
case_images: F3
case_images: She underwent decompressive surgery of the foramen magnum including a C1 laminectomy followed by occipitocervical fusion with intraoperative neurophysiological monitoring [Figure 3a]. Three months postoperatively, the MRI showed a reduction in ROPT and slightly resolution of the high cord signal [Figure 3b].