The Efficacy of Atlantoaxial Facet Joint Distraction and Fixation and Foramen Magnum Decompression for Chiari Type 1 Malformation with Basilar Invagination: A Case Report.

Foramen magnum decompression is an established surgical method for the treatment of Chiari type 1 malformation with syringomyelia. However, in some cases, neurologic symptoms that improve only after foramen magnum decompression may deteriorate again, and it has been suspected that increased instability of the craniocervical junction may be a factor. We report a case of Chiari type 1 malformation accompanied by basilar invagination and syringomyelia in which atlantoaxial facet joint distraction and fixation was performed as a revision surgery for deteriorating neurologic symptoms after foramen magnum decompression. The patient was a 16-year-old boy with chief complaints of gait disturbance and repeated falls. He was diagnosed with Chiari type 1 malformation accompanied by basilar invagination and syringomyelia. The clivo-axial angle was narrow at 105.8°. Initially, only foramen magnum decompression was performed, and the symptoms were relieved after the procedure but re-exacerbated within 2 weeks. The condition was speculated to have worsened instability at the atlantoaxial segment and ventral medullary compression; then, atlantoaxial facet joint distraction and fixation was performed secondarily, and symptoms improved. There is no clear surgical standard for performing foramen magnum decompression, atlantoaxial facet joint distraction and fixation, or a combination of both for Chiari type 1 malformation. Foramen magnum decompression provides horizontal decompression at the craniocervical junction, and atlantoaxial facet joint distraction and fixation achieves vertical indirect decompression of the ventral medulla and stabilization of the atlantoaxial segment in case with basilar invagination. Our experience suggests that combined foramen magnum decompression and atlantoaxial facet joint distraction and fixation may be particularly beneficial in Chiari type 1 malformation cases with basilar invagination and narrow clivo-axial angle.