title: Syndrome of occipitoatlantoaxial hypermobility, cranial settling, and chiari malformation type I in patients with hereditary disorders of connective tissue.
abstract: OBJECTIVE
  Chiari malformation Type I (CM-I) is generally regarded as a disorder of the paraxial mesoderm. The authors report an association between CM-I and hereditary disorders of connective tissue (HDCT) that can present with lower brainstem symptoms attributable to occipitoatlantoaxial hypermobility and cranial settling.
  
  
  METHODS
  The prevalence of HDCT was determined in a prospectively accrued cohort of 2813 patients with CM-I. All patients underwent a detailed medical and neuroradiological workup that included an assessment of articular mobility. Osseous structures composing the craniocervical junction were investigated morphometrically using reconstructed 3D computed tomography and plain x-ray images in 114 patients with HDCT/CM-I, and the results were compared with those obtained in patients with CM-I (55 cases) and healthy control individuals (55 cases).
  
  
  RESULTS
  The diagnostic criteria for Ehlers-Danlos syndrome and related HDCT were met in 357 (12.7%) of the 2813 cases. Hereditability was generally compatible with a pattern of autosomal dominant transmission with variable expressivity. The diagnostic features of HDCT/CM-I were distinguished from those of CM-I by clinical stigmata of connective tissue disease, a greater female preponderance (8:1 compared with 3:1, p < 0.001), and a greater incidence of lower brainstem symptoms (0.41 compared with 0.11, p < 0.001), retroodontoid pannus formation (0.71 compared with 0.11, p < 0.001), and hypoplasia of the oropharynx (0.44 compared with 0.02, p < 0.001). Measurements of the basion-dens interval, basion-atlas interval, atlas-dens interval, dens-atlas interval, clivus-atlas angle, clivus-axis angle, and atlas-axis angle were the same in the supine and upright positions in healthy control individuals and patients with CM-I. In patients with HDCT/CM-I, there was a reduction of the basion-dens interval (3.6 mm, p < 0.001), an enlargement of the basion-atlas interval (3.0 mm, p < 0.001), and a reduction of the clivus-axis angle (10.8 degrees, p < 0.001), clivus-atlas angle (5.8 degrees, p < 0.001), and atlas-axis angle (5.3 degrees, p < 0.001) on assumption of the upright position. These changes were reducible by cervical traction or returning to the supine position.
  
  
  CONCLUSIONS
  The identification of HDCT in 357 patients with CM-I establishes an association between two presumably unrelated mesodermal disorders. Morphometric evidence in this cohort-cranial settling, posterior gliding of the occipital condyles, and reduction of the clivus-axis angle, clivus-atlas angle, and atlas-axis angle in the upright position-suggests that hypermobility of the occipitoatlantal and atlantoaxial joints contributes to retroodontoid pannus formation and symptoms referable to basilar impression.
authors: Department of Neurosurgery, The Chiari Institute, Harvey Cushing Institute of Neuroscience, North Shore-Long Island Jewish Health System, Manhasset, New York 11030, USA. Milhorat@nshs.edu
authors: Thomas H
authors: TH
authors: Milhorat
authors: Paolo A
authors: PA
authors: Bolognese
authors: Misao
authors: M
authors: Nishikawa
authors: Nazli B
authors: NB
authors: McDonnell
authors: Clair A
authors: CA
authors: Francomano
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001139:Arnold-Chiari Malformation / Q000150:complications* / Q000000981:diagnostic imaging / Q000628:therapy; D001268:Atlanto-Axial Joint / Q000000981:diagnostic imaging; D001269:Atlanto-Occipital Joint / Q000000981:diagnostic imaging; D002648:Child; D002675:Child, Preschool; D015331:Cohort Studies; D003240:Connective Tissue Diseases / Q000150:complications* / Q000235:genetics* / Q000628:therapy; D004535:Ehlers-Danlos Syndrome / Q000150:complications / Q000235:genetics; D005260:Female; D005799:Genes, Dominant; D006801:Humans; D007091:Image Processing, Computer-Assisted; D021621:Imaging, Three-Dimensional; D007593:Joint Instability / Q000000981:diagnostic imaging / Q000209:etiology*; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D012886:Skull / Q000000981:diagnostic imaging*; D013577:Syndrome; D014057:Tomography, X-Ray Computed; D014143:Traction