Clinical Phenotype and Surgical Strategy as Predictors of Long-Term Outcome in Chiari I Malformation: A 4-Year Cohort Study

Chiari I malformation (CMI) is defined by caudal displacement of the cerebellar tonsils below the foramen magnum. Although tonsillar descent is the radiological hallmark, its correlation with symptom severity and surgical outcome remains inconsistent. The objective of this study is to identify clinical, radiological, and surgical predictors of favorable long-term outcome following posterior fossa decompression in patients with CMI. A retrospective cohort study of 42 consecutive patients undergoing posterior fossa decompression with a minimum follow-up of 3 years (mean: 4.3 years). Preoperative clinical and magnetic resonance imaging parameters were analyzed. Outcome was assessed using the Chicago Chiari Outcome Scale (CCOS). Favorable outcome was defined as CCOS ≥ 13. Twenty-seven patients (64.3%) achieved favorable outcome. Syringomyelia was present in 16.7% and was not associated with improved outcome. Bone-only decompression yielded higher favorable rates compared with duraplasty (70.5 vs. 37.5%). Postoperative complications were strongly associated with unfavorable outcome. Long-term surgical benefit in CMI depends primarily on clinical phenotype and postoperative course rather than tonsillar descent alone. Bone-only decompression appears effective in selected patients, and complication avoidance is critical to optimizing outcome.