title: The frequency and clinical significance of congenital defects of the posterior and anterior arch of the atlas.
abstract: OBJECTIVE
  In this study the authors investigated the anatomical, clinical, and imaging features as well as incidence of congenital defects of the C-1 arch.
  
  
  METHODS
  The records of 1104 patients who presented with various medical problems during the time between January 2006 and December 2006 were reviewed retrospectively. The craniocervical computed tomography (CT) scans obtained in these patients were evaluated to define the incidence of congenital defects of the posterior arch of C-1. In addition, 166 dried C-1 specimens and 84 fresh human cadaveric cervical spine segments were evaluated for anomalies of the C-1 arch.
  
  
  RESULTS
  Altogether, 40 anomalies (2.95%) were found in 1354 evaluated cases. Of the 1104 patients in whom CT scans were acquired, 37 (3.35%) had congenital defects of the posterior arch of the atlas. The incidence of each anomaly was as follows: Type A, 29 (2.6%); Type B, six (0.54%); and Type E, two (0.18%). There were no Type C or D defects. One patient (0.09%) had an anterior arch cleft. None of the reviewed patients had neurological deficits or required surgical intervention for their anomalies. Three cases of Type A posterior arch anomalies were present in the cadaveric specimens.
  
  
  CONCLUSIONS
  Most congenital anomalies of the atlantal arch are found incidentally in asymptomatic patients. Congenital defects of the posterior arch are more common than defects of the anterior arch.
authors.affiliation: Division of Neurological Surgery, Barrow Neurological Institute, St. Joseph's Hospital and Medical Center, Phoenix, Arizona 85013, USA. mehmetsenoglu@hotmail.com
authors.forename: Mehmet
authors.initials: M
authors.lastname: Senoglu
authors.forename: Sam
authors.initials: S
authors.lastname: Safavi-Abbasi
authors.forename: Nicholas
authors.initials: N
authors.lastname: Theodore
authors.forename: Nicholas C
authors.initials: NC
authors.lastname: Bambakidis
authors.forename: Neil R
authors.initials: NR
authors.lastname: Crawford
authors.forename: Volker K H
authors.initials: VK
authors.lastname: Sonntag
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002102:Cadaver; D001270:Cervical Atlas / Q000002:abnormalities*; D002648:Child; D004210:Dissection; D005260:Female; D006801:Humans; D015994:Incidence; D008297:Male; D008875:Middle Aged; D009139:Musculoskeletal Abnormalities / Q000150:complications / Q000000981:diagnostic imaging* / Q000453:epidemiology*; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed