Fig. 1

T1-weighted, post-contrast injection magnetic resonance imaging images show an enhancing lesion at an extradural location with an intradural extension at the right side of the C1/C2 vertebrae in the coronal (a), sagittal (b), and axial (c) plane. The mass effect caused corresponding spinal cord compression with left posterolateral displacement. No obvious cord signal abnormality was seen. Plain film readiographs of the preoperative cervical spine in the anteroposterior (d) and lateral view (e) also show the measured angle of occiput-C2 (blue), C1–C2 (red), and Takami’s angle (yellow) of − 23°, − 27°, and 104°, respectively