The following lateral C-Spine x-ray is from a 20 year old with neck pain post MVA. What can you notice? (It is subtle)
The lateral neck x-ray is normal. The 3 arcuate lines (anterior vertebral line, posterior vertebral line and the spinolaminar lines) are well aligned. There is a focal bulge anterior to C5. The c spine was cleared later based on other views and clinical assessment.
The patient has a bony ring on the atlas posteriorly, the arcuate foramen, which is a normal variant of the atlas; this is also called as a Kimmerle anomaly.
A normal lateral c-spine x-ray below for comparison:
The bony bridge is formed by calcification of the posterior atlanto-occipital membrane. The vertebral artery passes through the arcuate foramen and enters the foramen magnum; the foramen also contains the vertebral veins and the first cervical nerve.
Partial ossification is found in up to 35% of the population and a complete ring-like form in up to 15%.
There is an association with vertebrobasilar insufficiency and chronic upper cervical syndrome. However, the majority are asymptomatic. Forceful neck manipulation in the presence of this anomaly can lead to vertebral artery dissection.
(Reference: Yochum and Rowe’s essentials of skeletal radiology)