C2 segmental type of vertebral artery on the unfused side of partially occipitalized atlas.

Patients with craniovertebral junction anomalies are more likely to undergo craniovertebral junction procedures because of neurologic complications. Vertebral arteries (VAs) are more prone to injury in these cases because of an often anomalous course, with potentially disabling or grave sequel. In our patient with partially occipitalized atlas, CT angiogram revealed that 1 of the VAs passed through the bony canal in the occipitalized and/or fused bone, whereas the VA on unfused side was also unexpectedly anomalous and of C2 segmental type. To the best of our knowledge, such anomaly has never been reported in studies of patients with occipitalized atlas in the literature.