The effectiveness of optic nerve sheath diameter in surgical decision-making for type I Chiari malformations

This study evaluates the relationship between optic nerve sheath diameter (ONSD), measured through magnetic resonance imaging (MRI), and increased intracranial pressure (ICP) in patients with Type I Chiari malformation (CM).

This retrospective study includes 61 patients who underwent surgery for type I CM between January 2011 and January 2025. Patient data, including age, sex, presenting symptoms, presence of syringomyelia, comorbidities, type of dural opening technique, postoperative complications, and ONSD measured preoperatively and postoperatively through MRI, were analyzed. All MRIs were performed using a 1.5 Tesla scanner. ONSD measurements were made manually on axial T2-weighted sequences, 3 mm posterior to the optic disc in the mediolateral direction. The data were evaluated by two independent researchers. P <0.05 was considered statistically significant. The mean patient age was 32.6 years, with 75.4% being female. The most common symptom was headache (83.6%). The mean preoperative ONSD was 4.91 mm, while the mean postoperative ONSD was 4.26 mm, indicating a statistically significant reduction after surgery (P = 0.000). Duroplasty was performed in 50.8% of cases, while 49.2% underwent dural splitting. Cerebrospinal fluid fistulas were observed exclusively in the duroplasty group.

The significant postoperative reduction in ONSD, as measured by MRI, suggests that ONSD may serve as a noninvasive biomarker reflecting ICP changes and could be a useful tool in surgical decision-making and follow-up for type I CM.