PREVALENCE OF SELECT ANATOMICAL VARIANTS OF THE ATLAS AND CRANIOVERTEBRAL JUNCTION IN A KENYAN POPULATION

Abstract

Background: The atlas and the craniovertebral junction are known to present anatomical variations such as complete or incomplete ossification of the posterior atlantooccipital membrane over the vertebral artery groove resulting in the formation of a ponticulusposticus and arcuate foramen. These variations have been associated with vertebrobasilar insufficiency symptoms, various types of headaches, and acute hearing loss. Other variants include posterior arch defects of the atlas and its occipitalization. The knowledge of these variants may also reduce complications during lateral mass screw fixation of the atlas, posterior laminectomy and endovascular surgery. Methods: 116 CT scans from the Kenyatta National Hospital were used to study the prevalence of ponticulusposticus, arcuate foramina, posterior arch defects and occipitalization of the atlas. Results: A ponticulusposticus was more likely to be reported bilaterally (16.4%) on the atlas rather than ipsilaterally, with a prevalence of 36.2%. An arcuate foramen, though, was only found in 15.5% of the atlases. Only midline posterior arch defects (Type A) of the atlas were discovered in the study population, with a prevalence of 6.9%. Not a single case of occipitalization of the atlas was noted. Conclusions: The Kenyan population presents with fairly common atlantal and craniovertebral junction anatomical variants that should be considered when diagnosing and managing conditions whose aetiology is suspected to be tied to those regions.