Unfused anterior and posterior arches of C1

Case contributed by Varun Babu
Diagnosis certain


Head injury patient came for a routine screening non contrast study of the brain.

Patient Data

Age: 50 years
Gender: Female

No intracranial hemorrhage. No calvarial or skull base fracture. Non fusion of anterior and posterior arches of atlas with well-corticated margins and showing degenerative changes. Wider gap seen in posterior midline more than anterior. 

Case Discussion

Congenital non-fusion of the arches of the atlas (C1) needs to be distinguished from fractures of the arch. This anatomical variant has to be kept in mind especially as it could get mistaken for a fracture by non-radiologists.

Findings in favor of congenital non-fusion:

  1. typical appearance of a non-fused posterior arch
  2. well-corticated margins of the separated bone
  3. degenerative changes of the separated bone margins i.e. it is chronic
  4. (old imaging showing similar appearances - not in this case)

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