title: External validity of the chiari severity index and outcomes among pediatric chiari I patients treated with intra- or extra-Dural decompression.
abstract: BACKGROUND
  Chiari malformation type-1 (CM-1) may be treated by intradural (ID) or extradural (ED) posterior fossa decompression, although the optimal approach is debated. The Chiari Severity Index (CSI) is a pre-operative metric to predict patient-defined improvement after CM-1 surgery. In this study, we evaluate the results of ID versus ED decompression and assess the external validity of the CSI.
  
  
  METHODS
  We performed a retrospective cohort study of pediatric CM-1 patients undergoing decompression at a single academic children's hospital. Characteristics of headache, syrinx, and myelopathy were collected to derive CSI grade. The primary outcome measure was pre-operative symptom resolution. The proportion of patients with favorable outcome was tabulated for each of the three CSI grades and compared to previously published results.
  
  
  RESULTS
  From 2004 to 2014, 189 patients underwent ID (48%) or ED (52%) decompression at the Children's Hospital of Philadelphia (CHOP). Follow-up ranged from 1 to 75 months. Rates of symptom resolution (58-64%) and reoperation (8%) were similar regardless of surgical approach. Although proportions of favorable outcomes differed between the CHOP and Washington University (WU) cohorts, the difference was not related to CSI grade (p = 0.63). Furthermore, there was no difference in the proportion of favorable outcomes between the two cohorts regardless of ID (p = 0.26) or ED approach (p = 0.11).
  
  
  CONCLUSIONS
  Equivalent rates of symptom resolution and reoperation following ID and ED decompression support the ED approach as a first-line surgical option for pediatric CM-1 patients. In addition, our findings provide preliminary evidence supporting the generalizability of the CSI and its use in future comparative trials.
authors.affiliation: Department of Neurosurgery, University of Pennsylvania, 3400 Spruce Street, 3rd Floor Silverstein Pavilion, Philadelphia, PA, 19104, USA. Jared.Pisapia@uphs.upenn.edu.
authors.forename: Jared M
authors.initials: JM
authors.lastname: Pisapia
authors.affiliation: Department of Neurosurgery, University of Pennsylvania, 3400 Spruce Street, 3rd Floor Silverstein Pavilion, Philadelphia, PA, 19104, USA.
authors.forename: Maxwell B
authors.initials: MB
authors.lastname: Merkow
authors.affiliation: Department of Neurosurgery, University of Pennsylvania, 3400 Spruce Street, 3rd Floor Silverstein Pavilion, Philadelphia, PA, 19104, USA.
authors.forename: Danielle
authors.initials: D
authors.lastname: Brewington
authors.affiliation: Division of Neurosurgery, The Children's Hospital of Philadelphia, Philadelphia, PA, USA.
authors.forename: Rosemary E
authors.initials: RE
authors.lastname: Henn
authors.affiliation: Department of Neurosurgery, University of Pennsylvania, 3400 Spruce Street, 3rd Floor Silverstein Pavilion, Philadelphia, PA, 19104, USA.|Division of Neurosurgery, The Children's Hospital of Philadelphia, Philadelphia, PA, USA.
authors.forename: Leslie N
authors.initials: LN
authors.lastname: Sutton
authors.affiliation: Department of Neurosurgery, University of Pennsylvania, 3400 Spruce Street, 3rd Floor Silverstein Pavilion, Philadelphia, PA, 19104, USA.|Division of Neurosurgery, The Children's Hospital of Philadelphia, Philadelphia, PA, USA.
authors.forename: Phillip B
authors.initials: PB
authors.lastname: Storm
authors.affiliation: Department of Neurosurgery, University of Pennsylvania, 3400 Spruce Street, 3rd Floor Silverstein Pavilion, Philadelphia, PA, 19104, USA.|Division of Neurosurgery, The Children's Hospital of Philadelphia, Philadelphia, PA, USA.
authors.forename: Gregory G
authors.initials: GG
authors.lastname: Heuer
mesh_terms: D000293:Adolescent; D001139:Arnold-Chiari Malformation / Q000000981:diagnostic imaging / Q000523:psychology / Q000601:surgery*; D002648:Child; D015331:Cohort Studies; D019299:Decompression, Surgical / Q000379:methods*; D004388:Dura Mater / Q000601:surgery; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D011788:Quality of Life; D015203:Reproducibility of Results; D012720:Severity of Illness Index; D016896:Treatment Outcome
keywords: Chiari; Chiari severity index; Extradural; Intradural; Outcome; Posterior fossa decompression; Syrinx