Timing of syrinx reduction and stabilization after posterior fossa decompression for pediatric Chiari malformation type I.

OBJECTIVE: The aim of this study was to determine the timeline of syrinx regression and to identify factors mitigating syrinx resolution in pediatric patients with Chiari malformation type I (CM-I) undergoing posterior fossa decompression (PFD). METHODS: The authors conducted a retrospective review of records from pediatric patients ( /= 50% decrease in the maximal anteroposterior syrinx diameter (MSD). The time to syrinx regression was determined using Kaplan-Meier analysis. Multivariate analysis was conducted using a Cox proportional hazards model to determine the association between preoperative, clinical, and surgery-related factors and syrinx regression. RESULTS: The authors identified 85 patients with CM-I/SM who underwent PFD. Within 3 months post-PFD, the mean MSD regressed from 8.1 +/- 3.4 mm (preoperatively) to 5.6 +/- 2.9 mm within 3 months post-PFD. Seventy patients (82.4%) achieved >/= 50% regression in MSD. The median time to >/= 50% regression in MSD was 8 months (95% CI 4.2-11.8 months). Using a risk-adjusted multivariable Cox proportional hazards model, the patients who underwent tonsil coagulation (n = 20) had a higher likelihood of achieving >/= 50% syrinx regression in a shorter time (HR 2.86, 95% CI 1.2-6.9; p = 0.02). Thirty-six (75%) of 45 patients had improvement in headache at 2.9 months (IQR 1.5-4.4 months). CONCLUSIONS: The maximum reduction in syrinx size can be expected within 3 months after PFD for patients with CM-I and a syrinx; however, the syringes continue to regress over time. Tonsil coagulation was associated with early syrinx regression in this cohort. However, the role of surgical maneuvers such as tonsil coagulation and arachnoid veil identification and sectioning in the overall role of CM-I surgery remains unclear.