title: Dimensions of the posterior fossa in patients symptomatic for Chiari I malformation but without cerebellar tonsillar descent.
abstract: BACKGROUND
  Chiari I malformation (CMI) is diagnosed by rigid radiographic criteria along with appropriate clinical symptomatology. The aim of this study was to investigate the dimensions of the posterior cranial fossa in patients without significant tonsillar descent but with symptoms comparable to CMI.
  
  
  METHODS
  Twenty-two patients with signs and symptoms comparable to CMI but without accepted radiographic criteria of tonsillar descent > 3-5 mm were referred to our clinic for evaluation. A history and physical examination were performed on all patients. In reviewing their MRI scans, nine morphometric measurements were recorded. The measurements were compared to measurements from a cohort of twenty-five individuals with cranial neuralgias from our practice.
  
  
  RESULTS
  For patients with Chiari-like symptomatology, the following statistically significant abnormalities were identified: reduced length of the clivus, reduced length of basisphenoid, reduced length of basiocciput, and increased angle of the tentorium. Multiple morphometric studies have demonstrated similar findings in CMI.
  
  
  CONCLUSIONS
  The current classification of CMI is likely too restrictive. Preliminary morphologic data suggests that a subgroup of patients exists with tonsillar descent less than 3 mm below the foramen magnum but with congenitally hypoplastic posterior fossa causing symptomatology consistent with CMI.
authors.affiliation: epartment of Neurological Surgery, Center for Cranial Nerve Disorders, Allegheny Neuroscience Institute, 420 East North Avenue, Suite 302, Pittsburgh, PA 15212-4746, USA. rsekula@wpahs.org
authors.forename: Raymond F
authors.initials: RF
authors.lastname: Sekula
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Jannetta
authors.forename: Kenneth F
authors.initials: KF
authors.lastname: Casey
authors.forename: Edward M
authors.initials: EM
authors.lastname: Marchan
authors.forename: L Kathleen
authors.initials: LK
authors.lastname: Sekula
authors.forename: Christine S
authors.initials: CS
authors.lastname: McCrady