The arcuate foramen (foramen arcuate atlantis, ponticulus posticus or posterior ponticle, or Kimerle anomaly) is a frequently encountered normal variant of the atlas and is easily appreciated on a lateral plain film of the craniocervical junction.
Incidence is ~8% (range 1-15%) and it is more common in females.
The arcuate foramen develops by calcification of the posterior atlanto-occipital membrane. The atlantic portion (V3) of the vertebral arteries pass through this foramen. It has a variable morphology, can be complete or incomplete and may be unilateral or bilateral.
- complete or incomplete bony arch is seen over the posterosuperior aspect of the atlas on lateral projections