title: Agenesis of the posterior arch of the atlas.
abstract: OBJECTIVE
  To illustrate the radiological findings and review the current literature concerning a rare congenital abnormality of the posterior arch of the atlas.
  
  
  METHODS
  An adult female without neurological symptoms presented with an absent posterior arch of the atlas, examined with plain films and helical computerized tomography. Complete agenesis of the posterior arch of the atlas is a rare entity that can be easily identified by means of plain films. Although it is generally asymptomatic, atlantoaxial instability and neurological deficits may occur because of structural instability. Computerized tomography provides a means of assessing the extent of this abnormality and can help evaluate the integrity of neural structures. Although considered to be rare entities, defects of the posterior arch of the atlas may be discovered as incidental asymptomatic findings in routine cervical radiographs. Familiarity with this abnormality may aid medical professionals in the correct management of these cases.
authors: Department of Radiology, School of Medicine, University of Campinas, Brazil.
authors: Martin
authors: M
authors: Torriani
authors: José Leonardo Goes
authors: JL
authors: Lourenco
mesh_terms: D000328:Adult; D001270:Cervical Atlas / Q000002:abnormalities* / Q000000981:diagnostic imaging; D005260:Female; D006801:Humans; D011859:Radiography