Occult congenital anomaly of the atlas presenting in the setting of acute trauma.

Congenital absence of the posterior arch of the atlas is rare. Its detection in the setting of acute trauma may be confusing and mimic a fracture. This case serves to highlight the adjunctive use of computed tomography in equivocal cases. Most patients can be managed conservatively, however operative treatment should be reserved for patients in whom atlanto-axial instability has been shown.