Comparison of Foramen Magnum and Foramen of Magendie Dredging Versus Posterior Fossa Decompression With Duraplasty in Adults With Chiari I Malformation-Syringomyelia: A Propensity-Matched Study

BACKGROUND AND OBJECTIVES: While neurosurgical posterior fossa decompression with duraplasty (PFDD) may provide clinical and radiological improvement for Chiari malformation-I (CM-I)-syringomyelia, the comparative efficacy and safety of PFDD without vs with intradural tonsillar manipulation (posterior fossa decompression with tonsil resection) has remained controversial for over 5 decades. METHODS: We conducted a retrospective cohort study of 1231 CM-I-syringomyelia patients treated at our institution from 2003 to 2024, comparing 2 techniques: standard PFDD and foramen magnum and foramen of magendie dredging (FMMD, a modified posterior fossa decompression with tonsil resection procedure). Propensity score matching was used to balance baseline characteristics between the 2 groups. The primary outcomes were syrinx regression >50%, while secondary outcomes encompassed symptom-related parameters, syrinx regression, complication-related parameters, and reoperation rate. RESULTS: A total of 1231 patients with CM-I were included, of whom 310 (25.2%) were in the PFDD group, and 921 (74.8%) were in the FMMD group. Per treatment analysis demonstrated no increase in odds of complications for FMMD ( P > .05). PFDD was noninferior to FMMD in clinical improvement and syrinx regression ( P = .147, P = .169, respectively). Syrinx regression (>50% reduction) was superior following FMMD (78% vs 60%, P < .001). PFDD had a higher rate of revision surgery than FMMD (15.5% vs 4.1%, log-rank P < .001). CONCLUSION: At our center, FMMD demonstrated greater effectiveness in managing syringomyelia, with higher rates of syrinx regression (>50% reduction), a lower rate of revision surgery, and no increase in complications compared with PFDD. Nonetheless, PFDD was similar to FMMD regarding clinical improvement and syrinx regression.