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Appropriate surgical procedures for Chiari type 1 malformation and associated syrinx based on radiological characteristics of the craniovertebral junction


Several surgical procedures can be applied for syrinx associated with Chiari type 1 malformation; however, it remains controversial as to which approach is the most effective. Here, we evaluated the indications and limitations of foramen magnum decompression (FMD) with or without dural plasty. Forty patients with Chiari type 1 malformation were surgically treated and followed up for > 12 months. Thirty-two patients (80.0%) underwent FMD with removal of only the outer dura mater layer, while eight patients underwent FMD with dural plasty. We evaluated surgery-related complications and preoperative radiological findings affecting syrinx shrinkage rates. Post-surgery, the mean syrinx shrinkage rates were 0.32 ± 0.44 in the outer layer-removal group and 0.72 ± 0.27 in the dural plasty group (P = 0.012). Surgery-related complications were less frequent, but reoperation was more frequent, in the outer layer-removal group. The extent of tonsillar descent significantly affected syrinx shrinkage in FMD with outer layer removal (P = 0.042). The outcomes of both approaches in patients with tonsillar descent < 10.0 mm were similar. The dura mater in the posterior fossa was thin, necessitating dural plasty with FMD, while the spinal dura was sufficiently thick for removal of the outer layer in the Chiari patients. These histological differences corresponded with the inferior margin of the cerebellar tonsil. Recognizing the appropriate surgical indication for achieving good post-procedural outcomes is necessary for reducing complications and improving outcomes of FMD for Chiari type 1 malformations.

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The authors express their gratitude to their colleagues in the Department of Neurosurgery, Shinshu University School of Medicine, for their daily contributions to patients with Chiari malformation and its associated syrinx. We thank Mr. Masanori Koinuma and Mr. Toru Mimura from the Center for Clinical Research, Shinshu University School of Medicine, Matsumoto, Japan, for statistical analysis support.


This work was supported by JSPS KAKENHI (grant no. JP15K10356).

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Correspondence to Kiyoshi Ito.

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The authors declare that they have no conflict of interests.

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The institutional review board of our hospital approved the study protocol, including the surgical procedure (No. 3532).

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Informed consent was obtained from all individual participants included in this study.

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Ito, K., Yamada, M., Horiuchi, T. et al. Appropriate surgical procedures for Chiari type 1 malformation and associated syrinx based on radiological characteristics of the craniovertebral junction. Neurosurg Rev (2019).

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  • Chiari type 1 malformation
  • Clinical outcome
  • Radiological characteristics
  • Surgical approach