CT angiographic evaluation of the V3 vertebral artery course in cases of occipitalized atlas, a study of 25 cases

Objectives: To study the relationship of the 3rd segment of the vertebral artery to the posterior arch of the atlas in patients with occipitalized atlas, using CT angiography. Methods: A retrospective study of 25 cases with complete or partially occipitalized atlas who underwent CT angiography evaluation. Fifty vertebral arteries were analyzed in relation to the respective/related half of the posterior arch of the atlas. Results: Out of 50 vertebral arteries, 35 (70%) were anomalous; 31 (62%) traversed though bony canal between the fused occiput and atlas, and 4 (8%) coursed between C1 and C2 (C2 segmental type of vertebral artery). Except one, all anomalous vertebral arteries were associated with a fused corresponding side of posterior arch of atlas. Conclusion: The V3 portion of the vertebral artery assumes an anomalous course at the craniovertebral junction in most cases of occipitalized atlas, and this is strongly determined by the fusion status of the posterior arch of the atlas. Aberrations in its course are still seen despite expectations based on this fusion status. Preprocedural CT Angiography provides accurate information of its course to prevent iatrogenic VA injuries. Advances in knowledge: CT Angiography should be performed before any procedures at the craniovertebral junction in cases of occipitalized atlas to prevent iatrogenic, potentially catastrophic injuries to vertebral artery due to its anomalous course in most of these cases. There are very few such studies in the literature, none in radiology literature. We also describe some rare cases, including a case never described in any literature.