Posterolateral protrusion of the vertebral artery over the posterior arch of the atlas: quantitative anatomical study using three-dimensional computed tomography angiography

Abstract

When there was no dominant side, mean distances from the most protrusive part of the VA to the posterior arch of the atlas were 6.73 +/- 2.35 mm (right) and 6.8 +/- 2.15 mm (left). When the left side of the VA was dominant, the distance on the left side (8.46 +/- 2.00 mm) was significantly larger than that of the right side (6.64 +/- 2.0 mm). When compared by age group (< or = 30 years, 31-60 years, and > or = 61 years), there were no significant differences in the extent of the protrusion. When there was no dominant side, the mean distances from the most protrusive part of the VA to the midline were 30.73 +/- 2.51 mm (right side) and 30.79 +/- 2.47 mm (left side). When the left side of the VA was dominant, the distance on the left side (32.68 +/- 2.03 mm) was significantly larger than that on the right side (29.87 +/- 2.53 mm). The distance from the midline to the intersection of the VA and inner cortex of the posterior arch of the atlas was approximately 12 mm, irrespective of the side of VA dominance. The distance from the midline to the intersection of the VA and outer cortex of the posterior arch was approximately 20 mm on both sides. Anatomical variations and anomalies were found as follows: bony bridge formation over the groove for the VA on the posterior arch of C-1 (9.3%), an extracranial origin of the posterior inferior cerebellar artery (8.2%), and a VA passing beneath the posterior arch of the atlas (1.8%). Conclusions There may be significant variation in the location and branches of the VA that may place the vessel at risk during surgical intervention. If concern is noted about the vulnerability of the VA or its branches during surgery, preoperative evaluation by CT angiography should be considered.