The impact of Duraplasty on Syrinx Size in Chiari type-1 Malformation Patients: A Post-hoc Analysis of a Randomized Controlled Trial

Introduction: Chiari type-1 malformation (CM) and syringomyelia (SM) are common, associated neurosurgical pathologies. The two main surgical treatments for these conditions are posterior fossa decompression with (PFDD) and without (PFD) duraplasty. In this post-hoc analysis, we provide an in-depth examination of radiological syrinx response from a randomized controlled trial comparing these two surgical approaches.

Methods: Demographic, baseline and follow-up radiographic data were obtained from a multicenter, cluster-randomized controlled trial conducted by the Park-Reeves Syringomyelia Research Consortium in which patients were randomized into PFD or PFDD treatments. A total of 143 pediatric patients ( < 21 years) with follow-up radiographic data (436±137 days) were included in the analysis.

Results: 143 subjects with appropriate radiologic follow-up data showed maximum syrinx diameter reduction of 1.75±2.25mm in the PFD (n=74) and 2.53±2.36mm in the PFDD (n=69) groups (p=0.045). Logistic regression model demonstrated that PFDD is associated with a meaningful increase in the odds of syrinx reduction (OR: 2.14, 95% CI 1.01-4.65), even when accounting for baseline tonsillar descent and initial syrinx diameter. Stratification by age quantiles revealed significant difference in syrinx reduction by treatment in the 10–15-year-old group compared to the < 5, 5–10, and >15 groups (PFD: -0.84 mm, PFDD: -2.47 mm, p=0.025). Maximum syrinx diameter increased in 12% of subjects (n=17): 14.8% of PFD patients (n=11) and 8.7% of PFDD patients (n=6) with a greater average increase in the PFD group (PFD: 5.65±2.75mm; PFDD: 5.08±5.08mm). However, in this subgroup, PFDD was still associated with a decrease in syrinx length (-1.67±3.13 vertebral levels) compared to PFD (0.45±3.30 vertebral levels), in which a slight increase was observed.

Conclusion : PFDD resulted in a significantly greater syrinx reduction compared to PFD, with a higher likelihood of reduction, especially in patients 10-15 years old. A lower percentage of patients treated with PFDD experienced an increase in syrinx diameter compared to patients treated with PFD.