The importance of vertebral artery proximity to the odontoid process during anterior odontoid approaches.

The proximity of the vertebral artery (VA) to the odontoid process makes it vulnerable to injury during surgery. Knowledge of the quantitative anatomy of the VA groove is therefore necessary. In this study we assessed the spatial relationship between the VA and the odontoid process on cadavers by direct measurement and in patients by CT angiography. Our goal was to measure the distances from the VA and vertebrobasilar junction to the odontoid tip. The VA and odontoid process of 10 craniocervical cadavers ("cadavers") and of 20 patients were evaluated and average measurements obtained. The measured parameters were: (i) distance from the right VA to the odontoid tip (right VA-odontoid tip); (ii) distance from the left VA to the odontoid tip (left VA-odontoid tip), and (iii) distance from the vertebrobasilar junction to the odontoid tip (vertebrobasilar-odontoid tip). On the cadavers, the right VA-odontoid tip distance was 11.55mm, the left VA-odontoid tip was 11.02mm, and the vertebrobasilar junction-odontoid tip distance was 24.55mm. In patients, using CT angiography, the right VA-odontoid tip distance was 11.47mm and the left VA-odontoid tip distance was 11.50mm. The VA-odontoid tip distance is important in anterior odontoid approaches. Since the odontoid process may be in close contact with the VA, the relationship between them should be evaluated preoperatively in all candidates for odontoid surgery using three-dimensional CT angiography.