The 270° circumferential microsurgical decompression of the foramen magnum in adult Chiari malformation Type I: single surgeon series of 130 patients with syringomyelia, neurologic and headaches outcomes.

OBJECTIVE Chiari malformation Type I (CM-I) is a craniocervical junction disorder associated with descent of the cerebellar tonsils >5mm. The prevalence of CM-I is common, including 0.5-3.5% in the general population, 0.56-0.77% on MRI, and 0.62% in anatomical dissection studies. We sought to measure our surgical outcomes related to resolution/improvement of headaches, neurological outcomes, and syringomyelia compared with published adult CM-I studies from 2000-2019. METHODS From December 2003-June 2018, the first author performed 270° circumferential decompression on adult (>18y) CM-I patients. At admission and follow-up, all parameters were numerically evaluated; headaches were self-reported on the VAS scale, neurological condition was evaluated using Karnofsky Performance Score and European Myelopathy Score (EMS), and syrinx width (if present) was measured on MRI by Grades I-IV. All parameters were analyzed, compared, and statistically tested. We compared results to our previously published and updated systematic review of operative adult CM-I studies (studies from 2014-2019). RESULTS In our series, 121/118 (98%) experienced headache improvements and 100% experienced neurological improvements. Complete syrinx resolution was experienced by 35/43 (81%); 8 (19%) demonstrated significant improvement. In data from published studies (2000-2019), only 79% experienced headache resolution, 77% improvement of neurological status, and 74% resolution/improvement of syrinx (mean). CONCLUSION Our modified 270° circumferential microsurgical foramen magnum decompression for adult CM-I may be beneficial in improvement of outcomes, namely in resolutions of the syrinx, neurological symptoms, and headaches. We also confirm the association of BMI with CM-I. Further studies are needed to confirm our results.