Effectiveness of C1 Laminectomy for Chiari Malformation Type 1: Posterior Fossa Volume Expansion and Syrinx-Volume Decrease Rate

PURPOSE: This study aimed to analyze the effect of foramen magnum decompression with C1 laminectomy (C1L) for Chiari malformation type 1 (CM-1) in terms of improving clinical symptoms, expanding posterior fossa volume, and decreasing syrinx volume. MATERIALS AND METHODS: Between January 2007 and June 2019, 107 patients with CM-1 were included. The median patient age was 13±13 years (range: 9 months–60 years), female-to-male ratio was 1:1, and average length of tonsil herniation was 13±5 mm (range: 5–24 mm). Surgical techniques were divided into four groups based on duraplasty or C1L usage. Among the study subjects, 38 patients underwent duraplasty and had their syrinx volumes measured separately on serial magnetic resonance imaging. A three-dimensional visualization software was used to evaluate the syrinx-volume decrease rate. RESULTS: Bony decompression exhibited a mere 20% volume expansion of the lower-half posterior fossa. C1L offered a 3% additional volume expansion, which rose to 5% when duraplasty was added (p=0.029). There were no significant differences in complication rate when C1L was combined with duraplasty (p=0.526). Syrinx volumes were analyzed in 38 patients who had undergone duraplasty. Among them, 28 patients who had undergone duraplasty without C1L demonstrated a 5.9% monthly decrease in syrinx volume, which was 7.5% in the remaining 10 patients with C1L (p=0.040). CONCLUSION: C1L was effective in increasing posterior fossa volume expansion, both with and without duraplasty. A more rapid decrease in syrinx volume occurred when C1L was combined with duraplasty.