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

Abstract

Purpose: This study aimed to analyze the effect of foramen magnum decompression with C1 laminectomy (C1L) for Chiari malfor-mation 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 pa-tients underwent duraplasty and had their syrinx volumes measured separately on serial magnetic resonance imaging. A three-di-mensional 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% addition-al volume expansion, which rose to 5% when duraplasty was added (p=0.029). There were no significant differences in complica-tion rate when C1L was combined with duraplasty (p=0.526). Syrinx volumes were analyzed in 38 patients who had undergone du-raplasty. 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.