title: Cerebellar and hindbrain motion in Chiari malformation with and without syringomyelia.
abstract: OBJECTIVE
  The pathogenesis of syringomyelia associated with Chiari malformation type I (CM-I) is unclear. Theories of pathogenesis suggest the cerebellar tonsils may obstruct CSF flow or alter pressure gradients, or their motion might act as a piston to increase CSF pressure in the spinal subarachnoid space. This study was performed to measure cerebellar tonsillar and hindbrain motion in CM-I and assess the potential contributions to syrinx formation.
  
  
  METHODS
  Sixty-four CM-I patients and 25 controls were retrospectively selected from a clinical database, and all subjects had undergone cardiac-gated cine balanced fast-field echo MRI. There were a total of 36 preoperative CM-I scans, which consisted of 15 patients with and 21 patients without syringomyelia. Nineteen patients underwent paired pre- and postoperative imaging. Anteroposterior (AP) and superoinferior (SI) movements of the tip of the cerebellar tonsils, obex, fastigium of the fourth ventricle, pontomedullary junction, and cervicomedullary junction were measured. The distance between the fastigium and tip of the tonsils was used to calculate tonsillar tissue strain (Δi/i0).
  
  
  RESULTS
  CM-I patients had significantly greater cerebellar tonsillar motion in both the AP and SI directions than controls (AP +0.34 mm [+136%], p < 0.001; SI +0.49 mm [+163%], p < 0.001). This motion decreased after posterior fossa decompression (AP -0.20 mm [-33%], p = 0.001; SI -0.29 mm [-36%]; p < 0.001), but remained elevated above control levels (AP +56%, p = 0.021; SI +67%, p = 0.015). Similar trends were seen for all other tracked landmarks. There were no significant differences in the magnitude or timing of motion throughout the hindbrain between CM-I patients with and without syringomyelia. Increased tonsillar tissue strain correlated with Valsalva headaches (p = 0.03).
  
  
  CONCLUSIONS
  Cerebellar tonsillar motion may be a potential marker of CM-I and may have use in tailoring surgical procedures. The lack of association with syringomyelia suggests that tonsillar motion alone is not the driver of syrinx formation. Tonsillar tissue strain may play a part in the pathophysiology of Valsalva headaches.
authors.affiliation: Faculty of Medicine, University of New South Wales;
authors.forename: Vannessa
authors.initials: V
authors.lastname: Leung
authors.affiliation: Faculty of Medicine and Health Sciences, Macquarie University; and.
authors.forename: John S
authors.initials: JS
authors.lastname: Magnussen
authors.affiliation: Faculty of Medicine and Health Sciences, Macquarie University; and.
authors.forename: Marcus A
authors.initials: MA
authors.lastname: Stoodley
authors.affiliation: Neuroscience Research Australia and Prince of Wales Clinical School, University of New South Wales, Sydney, Australia.
authors.forename: Lynne E
authors.initials: LE
authors.lastname: Bilston
mesh_terms: D000328:Adult; D001139:Arnold-Chiari Malformation / Q000601:surgery*; D002531:Cerebellum / Q000473:pathology*; D015170:Cerebrospinal Fluid Pressure / Q000502:physiology*; D019299:Decompression, Surgical / Q000379:methods; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009038:Motion; D011184:Postoperative Period; D012189:Retrospective Studies; D012249:Rhombencephalon / Q000601:surgery*; D013346:Subarachnoid Space / Q000503:physiopathology / Q000601:surgery*; D013595:Syringomyelia / Q000601:surgery*; D016896:Treatment Outcome; D055815:Young Adult
keywords: AP = anteroposterior; CLM = Chiari-like malformation; CM-I = Chiari malformation Type I; Chiari malformation; GRASS = gradient recalled acquisition in steady state; PC = phase contrast; PFD = posterior fossa decompression; SI = superoinferior; SSAS = spinal subarachnoid space; bFFE = balanced fast-field echo; balanced fast-field echo; brain motion; cerebellar tonsils; cervical; syringomyelia