title: Do the cerebellar tonsils move during flexion and extension of the neck in patients with Chiari I malformation? A radiological study with clinical implications.
abstract: BACKGROUND
  In the past, diagnosis of the Chiari I malformation has primarily been made on midsagittal MRI. We hypothesized that based on the frequent presentation of opisthotonos in patients with hindbrain hernia (primarily Chiari II malformation but sometimes Chiari I malformation) that the hyperextension might be a compensatory technique used by such patients to bring the cerebellar tonsils up out of the cervical spine.
  
  
  METHODS
  This prospective study reviewed imaging of patients with Chiari I malformation who underwent flexion/extension MRI for evaluation of their hindbrain herniation. Age-matched controls were used for comparison.
  
  
  RESULTS
  In general, there was elevation of the cerebellar tonsils with extension and increased descent with flexion of the cervical spine. In 72 % of patients, flexion of the neck resulted in descent of the cerebellar tonsils. In 64 % of patients, extension of the neck resulted in ascent of the cerebellar tonsils. In the 14 patients with an associated syrinx, 71 % were found to have caudal movement of the cerebellar tonsils with neck flexion, and only 43 % were observed to have any movement of the cerebellar tonsils in neck extension compared to patients without a syrinx where ascent of the tonsils was seen in only nine during neck extension. Two patients were observed to have the reverse finding of ascent of the cerebellar tonsils with neck flexion and descent of the cerebellar tonsils with neck extension. Five patients had no movement of the cerebellar tonsils in either flexion or extension of the neck, and one of these had a small syrinx.
  
  
  CONCLUSIONS
  Although minimal and not in all patients, we observed elevation of the herniated cerebellar tonsils with extension of the cervical spine in patients with Chiari I malformation. This finding provides evidence as to why some patients with hindbrain herniation present with opisthotonos and supports earlier findings that CSF flow is reduced at the craniocervical junction in flexion in patients with Chiari I malformation.
authors.affiliation: Seattle Science Foundation, Seattle, WA, USA. shane.tubbs@childrensal.org.
authors.forename: R Shane
authors.initials: RS
authors.lastname: Tubbs
authors.affiliation: Seattle Science Foundation, Seattle, WA, USA.
authors.forename: Christina M
authors.initials: CM
authors.lastname: Kirkpatrick
authors.affiliation: Neurological Surgery, Penn State Hershey Medical Center, Hershey, PA, USA.
authors.forename: Elias
authors.initials: E
authors.lastname: Rizk
authors.affiliation: Pediatric Neurosurgery Associates, Children's Healthcare of Atlanta, Atlanta, GA, USA.
authors.forename: Joshua J
authors.initials: JJ
authors.lastname: Chern
authors.affiliation: Swedish Neuroscience Institute, Seattle, WA, USA.
authors.forename: Rod J
authors.initials: RJ
authors.lastname: Oskouian
authors.affiliation: Pediatric Neurosurgery, Children's of Alabama, Birmingham, AL, USA.
authors.forename: W Jerry
authors.initials: WJ
authors.lastname: Oakes
mesh_terms: D000293:Adolescent; D001139:Arnold-Chiari Malformation; D001933:Brain Stem; D002648:Child; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D009333:Neck; D011187:Posture; D013116:Spinal Cord
keywords: Chiari I malformation; Foramen magnum; Motion; Movement; Tonsils