Arcuate Foramen: An Anatomical Variation in the Atlas Vertebrae

Background: Arcuate foramen is a variation in the posterior arch of atlas vertebrae. It is commonly called as Kimmerle’s anomaly, also known as Ponticulus Posticus. It is the product of the complete or incomplete ossification of the posterior atlantooccipital membrane over the vertebral artery groove resulting in the formation of arcuate foramen containing the vertebral artery and the posterior branch of the first cervical spinal nerve. Aims: The aim of the present study was to identify the percentage of incidence of arcuate foramen in the atlas and its clinical important. Materials and Methods: The study was conducted in the Department of Anatomy, Katihar Medical College, Katihar, India with 32 adult dried atlas vertebrae. Results: We found four (12.5%) atlas with arcuate foramen. One atlas having complete arcuate foramen and three having partial complete arcuate foramen. Conclusion: Awareness of this type of variation is very important for neurosurgeons and radiologist during their clinical practice. The presence of the arcuate foramen would also complicate screw placement during surgery. Clinical prescreening for signs of vertebrobasilar insufficiency is important for chiropractic and manual therapies. KEYWORDS: Atlas, Variation, Arcuate foramen, Vertebral artery, Atlantooccipital membrane.