Chiari 1 formation- redefined- Clinical and radiographic observations in 388 surgically treated cases.

Abstract: Objective The subject of Chiari formation is revisited and redefined. Results of surgical treatment of patients with Chiari formation by atlantoaxial fixation are presented. Material and Methods Three hundred and eighty eight patients with Chiari formation were surgically treated during the period 2010 to June 2019 and have been analyzed. Results Two hundred and sixty six patients had syringomyelia. Two hundred and three patients had no craniovertebral bone abnormality, 74 patients had Group A and 111 patients had Group B basilar invagination. Twenty-nine patients had been earlier treated by foramen magnum decompression surgery with or without duroplasty. Clinical parameters, analysis of video recordings both before and after surgery, and patient self-assessment were included in the analysis of outcome. Immediate postoperative and sustained clinical improvement was observed in 385 (99.4 %) patients. Conclusions Gratifying clinical outcome in a majority of patients following atlantoaxial fixation and without any manipulation of neural structures, dura or bone in the region of foramen magnum consolidates the viewpoint that atlantoaxial instability is the nodal point of pathogenesis of Chiari 1 formation. The study suggests that Chiari 1 formation may be a secondary natural neural alteration in the face of atlantoaxial instability. The role of foramen magnum decompression surgery will need to be reassessed.