Evaluation of MRI-based cervical alignment parameters following suboccipital decompression in adult Chiari Type 1 patients

Aim Chiari malformation type 1 (CM-1) involves the craniovertebral junction and may influence cervical sagittal alignment, particularly at the upper cervical level. However, postoperative changes in sagittal alignment parameters remain unclear. This study aimed to evaluate the effect of suboccipital decompression on cervical sagittal alignment parameters in adult CM-1 patients and to investigate the possible influence of syringomyelia. Methods Thirty-five adult patients who underwent suboccipital decompression for CM-1 were retrospectively analyzed. We evaluated preoperative and first-year postoperative cervical MRI data. We measured cervical lordosis (CL), C2–C7 sagittal vertical axis (CSVA), C7 slope, T1 slope, and O–C2 angle using a standardized MRI protocol. We performed a subgroup analysis based on the presence of syringomyelia. Results No statistically significant differences were observed between preoperative and postoperative measurements of CL, CSVA, C7 slope, or T1 slope. Subgroup analysis revealed no significant differences in global sagittal parameters between patients with and without syringomyelia. However, a significant difference in O–C2 angle change was observed between patients with and without syringomyelia, with a significant decrease in patients without syringomyelia. Conclusion Suboccipital decompression was not associated with significant changes in cervical sagittal alignment parameters in adult CM-1 patients at one-year follow-up. Although a significant difference in O-C2 angle change was observed according to syringomyelia status, further studies are needed to clarify its significance.