title: Factors contributing to improvement of syringomyelia after foramen magnum decompression for Chiari type I malformation.
abstract: BACKGROUND
  Although various surgical approaches have been proposed for treating syringomyelia associated with Chiari type I malformation, a standard method has yet to be established. we prospectively investigated the results of our surgical method: foramen magnum decompression combined with C1 laminectomy and excision of the outer layer of the dura mater.
  
  
  METHODS
  Twenty patients underwent surgery between 2000 and 2010 at our hospital. After surgery, the size of the syrinx decreased in 11 patients (decreased group) but remained unchanged in nine patients (unchanged group). The following parameters were compared: age at the time of surgery, duration of morbidity, improvement of preoperative symptoms, morphological type and length of the syrinx, presence or absence of scoliosis, cervical alignment, basal and clivo-axial angles, and postoperative subarachnoid space at the foramen magnum level.
  
  
  RESULTS
  Preoperative symptoms improved in all patients in the decreased group but in only one patient in the unchanged group. The average duration of morbidity was significantly shorter in the decreased group. Morphological examination revealed that the size of all central-type syrinxes decreased after surgery, whereas in all cases of deviated-type syrinx, size was unchanged. The average length of preoperative syrinx was significantly shorter in the decreased group. The postoperative subarachnoid space at the foramen magnum was enlarged in the entire decreased group, whereas residual narrowing of the space was observed in 44 % of patients in the unchanged group. No significant intergroup differences were observed in the other factors.
  
  
  CONCLUSIONS
  In patients with syringomyelia, a longer and deviated type of syrinx, a longer duration of morbidity, and postoperative residual narrowing of the subarachnoid space are associated with a poor prognosis after the surgical procedure. The pathogenesis of syringomyelia is inconsistent, and the choice of surgical technique for each pathological condition is important.
authors.affiliation: Department of Orthopedic Surgery, National Center for Musculoskeletal Disorders, National Hospital Organization, Murayama Medical Center, 2-37-1, Gakuen, Musashimurayama, Tokyo, 208-0011, Japan.
authors.forename: Narihito
authors.initials: N
authors.lastname: Nagoshi
authors.forename: Akio
authors.initials: A
authors.lastname: Iwanami
authors.forename: Yoshiaki
authors.initials: Y
authors.lastname: Toyama
authors.forename: Masaya
authors.initials: M
authors.lastname: Nakamura
mesh_terms: D000293:Adolescent; D000328:Adult; D001139:Arnold-Chiari Malformation / Q000150:complications / Q000175:diagnosis / Q000601:surgery*; D002648:Child; D019299:Decompression, Surgical; D005260:Female; D005539:Foramen Magnum / Q000601:surgery*; D006801:Humans; D007796:Laminectomy; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D013595:Syringomyelia / Q000175:diagnosis / Q000209:etiology / Q000601:surgery*; D016896:Treatment Outcome