Clinical Research Details Clinical Research Posterior Fossa Decompression with or without Duraplasty for Chiari type I Malformation with Syringomyelia Study Description The purpose of this research study is to compare the two most common surgical treatments for Chiari type I malformation with syringomyelia, posterior fossa decompression without or with duraplasty, in terms of effectiveness, Quality of Life, and surgical complications or patient harm. Inclusion/Exclusion Criteria Inclusion Criteria 1) Age ≤21 years old 2) Chiari malformation type I with ≥5 mm tonsillar ectopia 3) Syrinx diameter (recorded as the greatest antero-posterior or transverse diameter) 3-9 mm. 4) MRI of the brain and cervical and thoracic spine are required prior to surgery and available to be shared with the DCC PCORI CER-1503-29700 Version 6 March 01, 2021 17 Exclusion Criteria 1) Syrinx <3 mm and/or ≥10 mm 2) Neuro-imaging demonstrating basilar invagination (position of the superior tip of dens ³5 mm above Chamberlain’s line) 3) Neuro-imaging demonstrating clival canal angle <120° 4) Prior PFD, PFDD, or other surgery at the craniovertebral junction 5) CM+SM secondary to other pathology (e.g. a tumor) 6) Unable to share pre-decompression MRI of the brain and cervical and thoracic spine 7) Patients who do not wish to participate Investigators Philipp R. Aldana, M.D., FAANS, FAAP Neurosurgery